Magic of Chemical Reactions 2. - Bugs3.com
Magic of Chemical Reactions 2. - Bugs3.com
Magic of Chemical Reactions 2. - Bugs3.com
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24<br />
<strong>2.</strong><br />
<strong>Magic</strong> <strong>of</strong> <strong>Chemical</strong> <strong>Reactions</strong><br />
SCHOOL SECTION
MT EDUCARE LTD. SCIENCE & TECHNOLOGY<br />
Q.I (A) Fill in the blanks :<br />
1. Ice changing to water is an example <strong>of</strong> ....................... change.<br />
<strong>2.</strong> When copper powder is heated, ....................... is formed.<br />
3. The substances that undergo changes are called as ....................... .<br />
4. Reactants are represented on ....................... .<br />
5. Products are represented on ....................... .<br />
6. Conversion <strong>of</strong> oil to fats requires ....................... as catalyst.<br />
7. When vegetable oil is mixed with nickel as a catalyst, and heat it with<br />
hydrogen gas ....................... are obtained on cooling.<br />
8. The simple form <strong>of</strong> representation <strong>of</strong> chemical reaction in words is called<br />
....................... .<br />
9. If reactants or products are present as solution in excess <strong>of</strong> water, the<br />
symbol used is ....................... .<br />
10. According to ......................., the total mass <strong>of</strong> reactants is equal to the<br />
total mass <strong>of</strong> products during a chemical reaction.<br />
*11. The chemical formula <strong>of</strong> POP is ....................... .<br />
*1<strong>2.</strong> The chemical reaction during which hydrogen is lost is called as<br />
....................... .<br />
*13. Corrosion can be prevented by using ....................... .<br />
*14. When acids and alkalis react together, ....................... and .......................<br />
is formed.<br />
*15. The chemical reaction in which heat is evolved is called as .......................<br />
reaction.<br />
16. When oil and fats are oxidized or even allowed to stand for a long time,<br />
they become ....................... .<br />
Answers :<br />
1. physical <strong>2.</strong> copper oxide<br />
3. reactants 4. left hand side<br />
5. right hand side 6. Nickel<br />
7. fats 8. word equation<br />
9. aq 10. law <strong>of</strong> conservation <strong>of</strong> mass<br />
11. (CaSO 4 ) 2 .H 2 O 1<strong>2.</strong> oxidation reaction<br />
13. anti-rust solution, coating surface by paint,<br />
process like galvanizing and electro-plating<br />
14. salt and water 15. exothermic reaction<br />
16. rancid<br />
Q.I (B) Match the following :<br />
1. Column I Column II Column III<br />
Reactants Products Types <strong>of</strong> reactions<br />
(i) Fe + S (a) NaCl + H 2O 1. Oxidation<br />
(ii) CuSO 4 + Zn (b) 2CuO <strong>2.</strong> Neutralization<br />
(iii) 2Cu + O 2 (c) ZnSO 4 + Cu 3. Displacement<br />
(iv) HCl + NaOH (d) FeS 4. Combination<br />
Ans. (i - d, 4), (ii - c, 3), (iii - b, 1), (iv - a, 2).<br />
<strong>2.</strong> Column I Column II<br />
(i) Gain <strong>of</strong> oxygen a) <strong>Chemical</strong> change<br />
(ii) Digestion (b) Oxidation<br />
(iii) Iodine, Camphor (c) Balanced equation<br />
(iv) NaOH + HCl NaCl + H 2O (d) Sublimatory substances<br />
Ans. (i - b), (ii - a), (iii - d), (iv - c).<br />
SCHOOL SECTION 25
SCIENCE & TECHNOLOGY MT EDUCARE LTD.<br />
3. Column I Column II<br />
(i) Copper (a) Black colour<br />
(ii) Coper Sulphate (b) Peacock blue<br />
(iii) Silver chloride (c) White precipitate<br />
(iv) Copper oxide (d) Reddish brown<br />
Ans. (i - d), (ii - b), (iii - c), (iv - a).<br />
Q.I (C) State whether the following statements are true or false. If false<br />
write the corrected statement :<br />
1. <strong>Chemical</strong> change is a temporary change<br />
Ans. False. It is a permanent change.<br />
<strong>2.</strong> Camphor sublimes on heating.<br />
Ans. True.<br />
3. (g) indicates the physical state as solid.<br />
Ans. False. (g) indicates the physical state as gas.<br />
4. Conversion <strong>of</strong> quick lime to slaked lime is an example <strong>of</strong> displacement<br />
reaction.<br />
Ans. False. It is an example <strong>of</strong> combination reaction.<br />
5. When left over edible oil is heated, its smell turns foul and develops<br />
rancidity.<br />
Ans. True.<br />
Q.I (D) Find the odd man out :<br />
1. Cu, Fe, Mn, CuSO 4.<br />
Ans. CuSO 4 as it is a compound and rest all are elements.<br />
<strong>2.</strong> Conversion <strong>of</strong> milk to curd, Rusting <strong>of</strong> iron, Digestion <strong>of</strong> food, Water turns<br />
into ice.<br />
Ans. Water turns into ice as rest all are examples <strong>of</strong> chemical change.<br />
3. Action <strong>of</strong> heat on calcium carbonate, Action <strong>of</strong> light on silver bromide,<br />
Action <strong>of</strong> light on silver chloride, Action <strong>of</strong> sodium hydroxide on hydrochloric<br />
acid.<br />
Ans. Action <strong>of</strong> sodium hydroxide on hydrochloric acid as it is a neutralization<br />
reaction and rest are examples <strong>of</strong> decomposition reaction.<br />
4. Fe + S FeS, NH 3 + HCl NH 4Cl, H 2 + Cl 2 HCl, CaCO 3 CaO + CO <strong>2.</strong><br />
Ans. CaCO 3 CaO + CO 2, this is decomposition reaction and rest all combination<br />
reaction.<br />
5. , (g), (l), =.<br />
Ans. =. This sign is not used in chemical equation.<br />
6. SO 2 = sulphur dioxide, H 2S = hydrogen sulphide, K 2CrO 4 = potassium<br />
dichromate, NaNO 3 = sodium nitrate.<br />
Ans. K 2CrO 4 as it is potassium chromate and not potassium dichromate.<br />
7. Photosynthesis, Digestion, Respiration, Magnetization <strong>of</strong> iron nail.<br />
Ans. Magnetisation <strong>of</strong> iron nail as it is a physical change and rest are chemical<br />
change.<br />
Q.I (E) Write the correlated terms :<br />
1. Solid to liquid : Melting :: ....................... : Sublimation.<br />
Ans. Solid to gas.<br />
<strong>2.</strong> Reactants : Breaking <strong>of</strong> bonds :: Products: ....................... .<br />
Ans. Formation <strong>of</strong> bond.<br />
3. Physical change : Reversible :: <strong>Chemical</strong> change : ....................... .<br />
Ans. Irreversible.<br />
4. BaSO 4 : ....................... :: Copper sulphide : Black precipitate.<br />
Ans. White precipitate.<br />
26<br />
SCHOOL SECTION
MT EDUCARE LTD. SCIENCE & TECHNOLOGY<br />
Q.I (F) Classify the following into physical change and chemical change :<br />
1. Rusting <strong>of</strong> iron <strong>2.</strong> Water turns into ice<br />
3. Copper sulphate dissolved in water 4. Bending <strong>of</strong> iron nail<br />
5. Ripening <strong>of</strong> mango 6. Digestion <strong>of</strong> food<br />
7. Magnetisation <strong>of</strong> iron nail 8. Formation <strong>of</strong> compound<br />
9. Decaying <strong>of</strong> vegetables 10 Formation <strong>of</strong> blood<br />
11. Production <strong>of</strong> energy in body.<br />
Ans. Physical change <strong>Chemical</strong> change<br />
1. Water turns into ice 1. Rusting <strong>of</strong> iron<br />
<strong>2.</strong> Copper sulphate dissolved in water <strong>2.</strong> Ripening <strong>of</strong> mango<br />
3. Bending <strong>of</strong> iron nail 3. Digestion <strong>of</strong> food<br />
4. Magnetisation <strong>of</strong> iron nail 4. Formation <strong>of</strong> compound<br />
5. Decaying <strong>of</strong> vegetables<br />
6. Formation <strong>of</strong> blood<br />
7. Production <strong>of</strong> energy in body<br />
Q.I (G) Classify the following into exothermic and endothermic reactions :<br />
1. Quick lime is added to water <strong>2.</strong> Potassium chlorate is heated<br />
3. Sodium dissolved in water 4. Mercuric oxide is strongly heated<br />
5. Neutralization <strong>of</strong> NaOH and HCl 6. Calcium carbonate is strongly heated<br />
7. Electrolysis <strong>of</strong> water 8. Zinc reacts with dil HCl<br />
Ans. Exothermic reactions Endothermic reactions<br />
1. Quick lime is added to water. 1. Potassium chlorate is heated.<br />
<strong>2.</strong> Sodium dissolved in water. <strong>2.</strong> Mercuric oxide is strongly heated.<br />
3. Neutralization <strong>of</strong> NaOH and HCl. 3. Calcium carbonate is strongly heated.<br />
4. Zinc reacts with dil HCl. 4. Electrolysis <strong>of</strong> water.<br />
Q.II Define the following :<br />
1. Reactants.<br />
Ans. Substances undergoing a chemical change are called as reactants.<br />
<strong>2.</strong> Products.<br />
Ans. The new substance formed as a result <strong>of</strong> chemical reaction is called as<br />
product.<br />
3. Word equation.<br />
Ans. The simple form <strong>of</strong> representation <strong>of</strong> chemical reaction in words is word<br />
equation.<br />
4. <strong>Chemical</strong> equation.<br />
Ans. The representation <strong>of</strong> chemical reaction with the help <strong>of</strong> chemical formulae<br />
is a chemical equation.<br />
5. Combination reaction.<br />
Ans. When two or more substances combine (mixture or compounds) to form a<br />
single product, then the reaction is called as combination reaction.<br />
6. Displacement reaction.<br />
Ans. When a more reactive element removes another element, having less<br />
reactivity, from its compound, this reaction is called as displacement reaction.<br />
MEMORISE :<br />
Reactivity series- Arrangement <strong>of</strong> metals in a vertical column in the order<br />
<strong>of</strong> decreasing reactivities is called reactivity series <strong>of</strong> metals. Here the<br />
most reactive metal is placed on top and less reactive is placed at the<br />
bottom.So, potassium is the most reactive metal and gold is least reactive.<br />
– Extra Information.<br />
SCHOOL SECTION 27
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7. Decomposition reaction.<br />
Ans. When a single reactant has broken down to give a simple product is known<br />
as decomposition reaction.<br />
8. Double displacement reaction.<br />
Ans. The reaction where a precipitate is formed by exchange <strong>of</strong> ions between<br />
the reactants is called as double displacement reaction. OR<br />
A chemical reaction in which constituents (radicals or ions)<strong>of</strong> two substances<br />
mutually exchange their places to form two new substances is called as<br />
double displacement reaction.<br />
9. Redox reaction.<br />
Ans. When oxidation and reduction takes place simultaneously in a given<br />
chemical reaction, it is called as redox reaction.<br />
10. Oxidation reaction.<br />
Ans. The chemical reaction in which reactants gain oxygen to form corresponding<br />
oxide. Similarly<br />
A chemical reaction in which reactants lose hydrogen to form product is<br />
called oxidation.<br />
11. Reduction reaction.<br />
Ans. The chemical reaction in which reactants gain hydrogen are reduction<br />
reactions. Similarly<br />
The reaction in which reactants lose oxygen atom to form product is called<br />
reduction.<br />
1<strong>2.</strong> Neutralization reaction.<br />
Ans. The reaction between acid and alkali to form salt and water is called as<br />
neutralization reaction.<br />
13. Corrosion.<br />
Ans. The slow process <strong>of</strong> decay or destruction <strong>of</strong> metal due to the effect <strong>of</strong> air,<br />
moisture, acids on it is called as corrosion.<br />
14. Exothermic reaction.<br />
Ans. The reaction in which heat is evolved is called as exothermic reaction.<br />
15. Endothermic reaction.<br />
Ans. The reaction in which heat is absorbed is called as endothermic reaction.<br />
16. Balanced equation.<br />
Ans. When number <strong>of</strong> atoms are same on the L.H.S. and R.H.S. <strong>of</strong> the chemical<br />
equation, then the equation is said to be a balanced equation.<br />
Q.III Give scientific reasons :<br />
*1. Grills <strong>of</strong> doors and windows are always painted before they are used.<br />
Ans. 1. Railings, iron bridges, grills <strong>of</strong> doors and windows, railway coaches,<br />
steel furniture, and bodies <strong>of</strong> truck, cars, buses are made <strong>of</strong> iron.<br />
<strong>2.</strong> To protect them from rusting, a coating <strong>of</strong> paint is applied. By doing<br />
this, air and moisture cannot come in contact with the iron object and<br />
hence rusting doesn’t takes place.<br />
So, grills <strong>of</strong> doors and windows are always painted before they are used.<br />
*<strong>2.</strong> Physical states <strong>of</strong> reactants and products are mentioned while writing<br />
a chemical equation.<br />
Ans. 1. The equation that gives more information about the chemical reaction<br />
is known as more informative or information giving equation.<br />
<strong>2.</strong> The chemical equation can be made more informative in three ways :<br />
(a) By indicating the physical states <strong>of</strong> reactants and products.<br />
(b) By indicating the heat changes taking place in the equation.<br />
(c) By indicating the conditions under which the reaction takes place.<br />
So, physical states <strong>of</strong> reactants and products are mentioned while<br />
writing a chemical equation.<br />
28<br />
SCHOOL SECTION
MT EDUCARE LTD. SCIENCE & TECHNOLOGY<br />
*3. Potassium ferrocyanide is stored in dark coloured bottles and kept away<br />
from sunlight.<br />
Ans. 1. Potassium ferrocyanide, (molecular formula is K 4[Fe(CN) 6].3H 2O) is a<br />
yellow coloured compound.<br />
<strong>2.</strong> If this compound gets exposed to sunlight then it will undergo<br />
decomposition reaction.<br />
3. Therefore, potassium ferrocyanide is stored in dark coloured bottles<br />
and kept away from sunlight.<br />
*4. Iron articles rust readily whereas steel which is also made <strong>of</strong> iron will<br />
not undergo corrosion.<br />
Ans. 1. Iron is a widely used metal but if it used in the pure form, it may rust.<br />
<strong>2.</strong> When a small amount <strong>of</strong> carbon (varying from 0.1% to 1.5% )is mixed<br />
with iron, we get an alloy called steel.<br />
3. This alloy <strong>of</strong> iron is hard and strong and is used for making nails,<br />
screw, bridges, railway lines, ships, construction <strong>of</strong> buildings, vehicles.<br />
4. An important property <strong>of</strong> alloy is that they resist corrosion.<br />
So, iron articles rust readily whereas steel which is also made <strong>of</strong> iron<br />
will not undergo corrosion.<br />
MEMORISE :<br />
An alloy is a homogeneous mixture <strong>of</strong> two or more metals( or a metal and<br />
small amount <strong>of</strong> non-metal). If iron metal is alloyed with other metals<br />
like chromium and nickel, we get stainless steel that does not rust at all.<br />
– Extra Information.<br />
*5. Edible oil is not allowed to stand for a long time in an iron or tin container.<br />
Ans. 1. Fats and edible oil when allowed to stand for a longer time in iron or<br />
tin container becomes rancid.<br />
<strong>2.</strong> The condition produced by oxidation <strong>of</strong> fats and oils in food marked by<br />
unpleasant smell and taste is called rancidity. When the oil is heated,<br />
it starts frothing and smells foul.<br />
3. If the food is cooked in rancid oil, it gives an unpleasant smell and<br />
taste, making it unfit for consumption.<br />
So, edible oil is not allowed to stand for a long time in an iron or tin<br />
container.<br />
6. Rusting <strong>of</strong> iron is a chemical change.<br />
Ans. 1. When iron is exposed to air, it gets oxidized by oxygen in air in the<br />
presence <strong>of</strong> moisture to form reddish brown coloured hydrated iron<br />
oxide. This process is called rusting <strong>of</strong> iron. The number <strong>of</strong> water<br />
molecules in the rust varies.<br />
4Fe (s) + 3O 2(g) + 2xH 2O (l) 2Fe 2O 3.H 2O (s)<br />
Iron Oxygen Water Hydrated iron oxide<br />
<strong>2.</strong> The chemical properties <strong>of</strong> iron oxide are different from iron and oxygen.<br />
3. We cannot obtain back iron from rust(iron oxide) by simple method i.e.<br />
change is irreversible.<br />
Hence rusting <strong>of</strong> iron is a chemical change.<br />
7. <strong>Chemical</strong> change is always associated with exchange <strong>of</strong> energy.<br />
Ans. 1. <strong>Chemical</strong> reaction or changes may take place spontaneously by bringing<br />
reactants in contact. This is usually accompanied by release <strong>of</strong> heat.<br />
<strong>2.</strong> During a chemical reaction, the bonds between the atoms <strong>of</strong> the<br />
reactants break. This is made possible by bringing reactants in contact<br />
and then by supplying energy like heat, electricity or light. As a result,<br />
products are formed.<br />
Thus, a chemical reaction is always associated with an exchange <strong>of</strong><br />
energy.<br />
SCHOOL SECTION 29
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8. Conversion <strong>of</strong> ice into water is a physical change.<br />
Ans. 1. On heating, ice melts into water and on the other hand when water is<br />
cooled, it freezes into ice.<br />
<strong>2.</strong> In this change, only the physical property <strong>of</strong> water i.e state <strong>of</strong> water<br />
changes as both ice and water chemically are water only. Therefore,<br />
no new substance is formed.<br />
Hence, conversion <strong>of</strong> ice into water is a physical change.<br />
9. Formation <strong>of</strong> a compound is a chemical change.<br />
Ans. 1. Compound is a substance produced by the chemical reaction between<br />
two or more elements in a fixed proportion.<br />
<strong>2.</strong> Both physical and chemical properties <strong>of</strong> the compound are different<br />
from the properties <strong>of</strong> its constituent elements.<br />
3. A new substance is formed, which can not be converted into original<br />
substance.<br />
Hence formation <strong>of</strong> a compound is a chemical change.<br />
10. Silver salts are kept in dark coloured bottles.<br />
Ans. 1. A chemical reaction that proceeds by absorption <strong>of</strong> light is called a<br />
photochemical reaction.<br />
<strong>2.</strong> Eg. When silver bromide is exposed to light, yellow colour <strong>of</strong> silver<br />
bromide changes to grey colour.<br />
Silver bromide is decomposed to form grey silver metal and bromine<br />
gas is liberated.<br />
30<br />
2AgBr (s)<br />
Sunlight<br />
2Ag (s) + Br 2(g)<br />
Silver bromide Silver metal Bromine gas.<br />
So, Silver salts are kept in dark coloured bottles.<br />
Q.IV Distinguish between :<br />
1. Physical change and <strong>Chemical</strong> change.<br />
Ans.<br />
Physical change<br />
1. In this change, the composition<br />
<strong>of</strong> substance does not change and<br />
no new substance is formed.<br />
<strong>2.</strong> There is a change only in<br />
physical properties.<br />
3. This change is temporary.<br />
4. The original substance can be<br />
recovered by simple means.<br />
5. Eg.: Steam is condensed.<br />
<strong>2.</strong> Exothermic reaction and Endothermic reacion.<br />
Ans. Exothermic reaction<br />
Endothermic reaction<br />
1. The reaction where heat energy<br />
is evolved or liberated is called<br />
as exothermic reaction.<br />
<strong>2.</strong> Temperature <strong>of</strong> the reaction<br />
mixture rises.<br />
3. Generally, the reactions are fast.<br />
4. Products are more stable.<br />
5. These reactions take place at<br />
lower temperatures.<br />
6. Eg.: Neutralization reaction.<br />
<strong>Chemical</strong> change<br />
1. In this change, the composition<br />
<strong>of</strong> substance changes and a new<br />
substance is formed.<br />
<strong>2.</strong> There is a change in both physical<br />
and chemical properties.<br />
3. This change is permanent.<br />
4. The original substance cannot be<br />
recovered by simple means.<br />
5. Eg.: Ripening <strong>of</strong> fruit, milk is<br />
converted to curd.<br />
1. The reaction where heat energy<br />
is absorbed is called as<br />
endothermic reaction.<br />
<strong>2.</strong> Temperature <strong>of</strong> the reaction<br />
mixture lowers.<br />
3. Generally, the reactions are slow.<br />
4. Reactants are more stable.<br />
5. These reactions take place at<br />
high temperatures.<br />
6. Eg.: Calcium is strongly heated.<br />
SCHOOL SECTION
MT EDUCARE LTD. SCIENCE & TECHNOLOGY<br />
Q.V Answer the following in detail :<br />
*1. What do you observe when H 2S gas is passed through cadmium chloride<br />
solution, name the type <strong>of</strong> reaction?<br />
Ans. When hydrogen sulphide gas is passed through cadmium chloride solution,<br />
it gives a yellow precipitate <strong>of</strong> cadmium sulphide and hydrochloric acid.<br />
CdCl 2(aq) + H 2S (g) CdS (l) + 2HCl (aq)<br />
It is a double displacement reaction.<br />
*<strong>2.</strong> What do you understand by the term redox reaction? Explain with one<br />
example.<br />
Ans. 1. When oxidation and reduction takes place simultaneously in a chemical<br />
reaction, it is termed as redox reaction.<br />
<strong>2.</strong> Eg.: When sulphur dioxide reacts with hydrogen sulphide, it forms water<br />
and sulphur.<br />
SO 2 + 2H 2S 2H 2O + 3S <br />
In this reaction, SO 2 is changing to S. This is removal <strong>of</strong> oxygen which<br />
is called as reduction. So, SO 2 is reduced to S. H 2S is changing to H 2O.<br />
This is addition <strong>of</strong> oxygen which is called as oxidation. So, H 2S is oxidized<br />
to H 2O.<br />
*3. What is corrosion? Do gold ornaments corrode, if not why?<br />
Ans. 1. The slow process <strong>of</strong> decay or destruction <strong>of</strong> metal due to effect <strong>of</strong> air,<br />
moisture, acids on it is called as corrosion.<br />
<strong>2.</strong> Gold is a yellow shining metal. Gold metal does not corrode because it<br />
is a highly unreactive metal that remains unaffected by air, water<br />
vapour, and other gases in the atmosphere. Gold does not tarnish and<br />
retains its luster for years. Since gold does not corrode, gold ornaments<br />
look new after years. break.<br />
3. This is achieved by bringing reactants in contact with each other and<br />
then by supplying energy in the form <strong>of</strong> either heat, light or electricity.<br />
4. This results in breaking <strong>of</strong> bonds in the reactants and rearrangement<br />
<strong>of</strong> atoms <strong>of</strong> reactants and formation <strong>of</strong> new bonds in the product.<br />
5. Thus, a chemical reaction is always associated with exchange <strong>of</strong> energy.<br />
*4. State the neutralization.<br />
Ans. 1. The reaction between acid and base to form salt and water is called as<br />
neutralization reaction.<br />
Acid + Base Salt + Water<br />
<strong>2.</strong> When an acid is treated with base, the base neutralizes the acid and<br />
destroys its acidity. Since an acid and base neutralize each other's<br />
effect, it is called as neutralization reaction.<br />
3. Eg.: When hydrochloric acid reacts with sodium hydroxide, then a<br />
neutralization reaction takes place to give salt and water.<br />
NaOH (aq)+ HCl (aq) NaCl (aq) + H 2O (l)<br />
MEMORISE :<br />
We can carry out this reaction in the laboratory and phenolphthalein is<br />
used as an indicator. – Extra Information.<br />
SCHOOL SECTION 31
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5. What are the steps <strong>of</strong> writing a chemical equation?<br />
Ans. 1. The symbols or molecular formulae <strong>of</strong> the reactants are written on the<br />
left hand side and products are on the right hand side.<br />
<strong>2.</strong> Reactants and products are connected with an arrow () pointing<br />
towards product side.<br />
3. Whenever there are two or more reactants, a plus (+) sign is written<br />
between each <strong>of</strong> them. Similarly, if there are two or more products, a<br />
plus sign is written between them.<br />
4. Certain reactions have to be carried out under specific condition such<br />
as temperature, pressure, catalyst. These condition are mentioned on<br />
the arrow pointing from reactants to product.<br />
5. The physical states <strong>of</strong> reactants and products are also mentioned in a<br />
chemical equation to make it more informative.<br />
6. The notations like g,l,s,aq are written in brackets as subscripts along<br />
with symbols/formulae <strong>of</strong> reactants and products.<br />
or (g) - Gas<br />
(l) - Liquid<br />
(s) - Solid<br />
(aq) - Aqueous solution<br />
- Precipitate.<br />
6. Take finely powdered zinc and allow it to react with CuSO 4. Then take<br />
zinc granules and carry out the same reaction. Which reaction takes<br />
place faster ?<br />
Ans. 1. The reaction is as follows :<br />
When zinc reacts with copper sulphate solution to give a water soluble<br />
compound zinc sulphate and reddish brown deposit <strong>of</strong> copper.<br />
Zn (s) + CuSO 4(aq) ZnSO 4(aq) + Cu (s)<br />
Zinc Copper sulphate Zinc sulphate Copper<br />
<strong>2.</strong> In solid reactants, the rate <strong>of</strong> a reaction depends upon size <strong>of</strong> particles.<br />
Smaller the size <strong>of</strong> particles, quicker is the reaction. This is because,<br />
in case <strong>of</strong> large solid reactants, only the molecules on surface are<br />
available for reaction. But if the reactants are finely powdered, the<br />
total surface area on all the smaller particles become much more and<br />
hence more number <strong>of</strong> molecules become available for reaction.<br />
3. So, the reaction takes place faster with powdered zinc than zinc granules.<br />
*7. We feel fresh while on a morning walk in natural surroundings. Why<br />
don’t we feel the same after 10 a.m. and during rush hours ? Write a<br />
chemical reaction to support your statement.<br />
Ans. 1. During early morning more amount <strong>of</strong> O 2 is available for cellular<br />
respiration. So, glucose is completely oxidise to release energy.<br />
C 6 H 12 O 6 + O 2 CO 2 + H 2 O + Energy (38 ATP)<br />
<strong>2.</strong> As the day progresses the level <strong>of</strong> O 2 decreases as compare to early<br />
morning this is due emission <strong>of</strong> other gases under this condition glucose<br />
releases only 2 ATP (energy) molecules.<br />
3. Since, more amount <strong>of</strong> energy is released in presence <strong>of</strong> O 2 and less<br />
amount <strong>of</strong> energy is released due to insufficient oxygen.<br />
32<br />
SCHOOL SECTION
MT EDUCARE LTD. SCIENCE & TECHNOLOGY<br />
MEMORISE :<br />
The rate <strong>of</strong> reaction is change in concentration <strong>of</strong> reactants and products<br />
in unit time. The rate <strong>of</strong> reaction also depends on :<br />
Nature <strong>of</strong> reactants, Size <strong>of</strong> particles, Concentration <strong>of</strong> reactants,<br />
Temperature and effect <strong>of</strong> catalyst.<br />
A catalyst is used to bring about a chemical reaction at low temperature<br />
and at a faster rate that reduces the production cost and increases<br />
pr<strong>of</strong>itability. – Extra Information.<br />
Q.VI Answer the following questions in one sentence each :<br />
1. What are the different types <strong>of</strong> reactions?<br />
Ans. There are four different types <strong>of</strong> reactions that are :<br />
1. Combination reaction <strong>2.</strong> Displacement reaction<br />
3. Decomposition reaction 4. Double displacement reaction.<br />
<strong>2.</strong> Carbohydrates like rice, potato, sago etc are major sources <strong>of</strong> energy in<br />
our diet. During digestion, these are broken down to glucose. Glucose<br />
combines with oxygen in our body and provides energy.<br />
Ans. C 6H 12O 6(aq) + 6O 2(g) 6CO 2(g) + 6H 2O (l) + Energy<br />
1. Is this an exothermic reaction?<br />
Ans. Since energy is released, it is an exothermic reaction<br />
3. When edible oil is converted to fats, what reaction is it? Express it in<br />
words.<br />
Ans. 1. Conversion <strong>of</strong> edible oils to fats is called as hydrogenation reaction.<br />
<strong>2.</strong> When H 2 gas is passed through edible oil in presence <strong>of</strong> Nickel which<br />
acts as a catalyst at high temperature. It gets converted into fats, this<br />
reaction is called as hydrogentation reaction.<br />
Edible oil + Hydrogen gas Ni/<br />
<br />
Fats<br />
4. What was the colour <strong>of</strong> precipitate formed ?<br />
Ans. When you add potassium chromate (K2CrO4) to barium sulphate solution<br />
(BaSO 4).<br />
K2CrO 4 + BaSO 4 BaCrO 4 + K2SO 4<br />
Potassium Barium Barium Potassium<br />
chromate sulphate chromate sulphate<br />
5. Name the precipitate.<br />
Ans. Barium chromate (BaCrO4) which is yellow in colour.<br />
6. Write balanced chemical equation.<br />
Ans. K2CrO 4 + BaSO 4 BaCrO 4 + K2SO 4<br />
7. According to you, is it a displacement reaction or double displacment<br />
reacion ?<br />
Ans. It is a double displacement reaction.<br />
Q.VII Balance the following chemical reactions with the help <strong>of</strong> balanced<br />
equations :<br />
1. H 2 + Cl 2 HCl<br />
Ans. H 2 + Cl 2 2HCl<br />
<strong>2.</strong> NH 3 + HCl NH 4Cl<br />
Ans. The equation is already balanced, so it is a self balanced equation.<br />
SCHOOL SECTION 33
SCIENCE & TECHNOLOGY MT EDUCARE LTD.<br />
3. ZnS + O 2 ZnO + SO 2<br />
Ans. 2ZnS + 3O 2 2ZnO + 2SO 2 <br />
4. CaCO3 <br />
Heat CaO + CO2 Ans. The equation is already balanced, so it is a self balanced equation.<br />
5. H 2S + O 2 H 2O + SO 2<br />
Ans. 2H 2S + 3O 2 2H 2O + 2SO 2 <br />
6. AgNO 3 + H 2S HNO 3 + Ag 2S<br />
Ans. 2AgNO 3+ H 2S 2HNO 3 + Ag 2S <br />
7. NaOH + CO 2 Na 2CO 3 + H 2O<br />
Ans. 2NaOH + CO 2 Na 2CO 3 + H 2O<br />
8. Identify the following reactions as combination, decomposition,<br />
34<br />
displacement, double displacement reaction.<br />
1. H 2 + Cl 2 2HCl<br />
Ans. Combination reaction.<br />
<strong>2.</strong> 2HgO <br />
Heat 2Hg + O2 <br />
Ans. Thermal decomposition reaction.<br />
3. NH 3 + HCl NH 4Cl<br />
Ans. Combination reaction.<br />
4. BaCl 2 + H 2SO 4 BaSO 4 + 2HCl<br />
Ans. Double displacement reaction.<br />
5. Zn + 2HCl ZnCl 2 + H 2 <br />
Ans. Displacement reaction.<br />
6. CuSO 4 + Fe FeSO 4 + Cu<br />
Ans. Displacement reaction.<br />
7. 2KClO3 <br />
Heat 2KCl + 3O2 <br />
Ans. Thermal decomposition reaction.<br />
8. 2KI + Cl 2 2KCl + I 2<br />
Ans. Displacement reaction.<br />
9. C + O 2 CO 2 <br />
Ans. Combination reaction.<br />
10.CaO + H 2O Ca(OH) 2 + heat<br />
Ans. Combination reaction.<br />
MEMORISE :<br />
To get the molecular formula <strong>of</strong> a compound:<br />
Eg. : Sodium chloride<br />
Symbol Na Cl<br />
Valency 1 1<br />
Criss cross Na 1 Cl 1<br />
i.e. NaCl – Extra Information.<br />
SCHOOL SECTION
MT EDUCARE LTD. SCIENCE & TECHNOLOGY<br />
16. Write the formulae <strong>of</strong> the following :<br />
Name <strong>of</strong> compound Formula<br />
Potassium chromate K 2CrO 4<br />
Iron sulphide FeS<br />
Copper oxide CuO<br />
Hydrogen sulphide H 2S<br />
Sulphur dioxide SO 2<br />
Carbonic acid H 2CO 3<br />
Plaster <strong>of</strong> Paris (CaSO 4) <strong>2.</strong>H 2O<br />
Potassium nitrate KNO 3<br />
Calcium carbonate CaCO 3<br />
Quick lime or calcium oxide CaO<br />
Calcium hydroxide or slaked lime Ca(OH) 2<br />
Silber bromide AgBr<br />
Calcium sulphide CaS<br />
Barium sulphate BaSO 4<br />
Ethyl alcohol C 2H 5OH<br />
Methane CH 4<br />
1. Sulphur dioxide reacts with hydrogen sulphide<br />
Ans. When sulphur dioxide reacts with hydrogen sulphide to give sulphur and<br />
water.<br />
SO 2(g) + 2H 2S (g) 3S (g) + 2H 2O (l)<br />
Sulphur dioxide Hydrogen sulphide Sulphur Water<br />
<strong>2.</strong> Copper is exposed to air.<br />
Ans. When copper is exposed to air, copper gets oxidized to form black coloured<br />
copper oxide.<br />
2Cu (s) + O 2(g) 2CuO (s)<br />
Copper Oxygen Copper oxide<br />
3. Iron sulphide reacts with sulphuric acid.<br />
Ans. When iron sulphide reacts with sulphuric acid to give ferrous sulphate<br />
and hydrogen sulphide gas is liberated.<br />
FeS (s) + H 2SO 4(aq) FeSO 4(aq) + H 2S (g)<br />
Ferrous sulphide Sulphuric acid Ferrous sulphate Hydrogen sulphide<br />
4. Iron reacts with sulphur.<br />
Ans. When iron reacts(heated) with sulphur to give iron sulphide.<br />
Fe (s) + S (s) <br />
FeS (s)<br />
Iron Sulphur Iron sulphide<br />
5. Plaster <strong>of</strong> Paris is mixed with water.<br />
Ans. When Plaster <strong>of</strong> Paris is mixed with proper quantity <strong>of</strong> water, it shows a<br />
remarkable property <strong>of</strong> setting into a hard mass called gypsum.<br />
(CaSO 4) 2, H 2O + 3H 2O 2(CaSO 4, 2H 2O) + Heat energy<br />
Plaster <strong>of</strong> Paris Gypsum<br />
6. Cement with sand and gravel reacts with water at new construction<br />
sites.<br />
Ans. Cement with sand and gravel reacts with water to form concrete that<br />
imparts strength to the building. This is an exothermic reaction.<br />
3CaO.Al 2O 3 + 6H 2O (l) 3CaO.Al 2O 3.6H 2O + Heat<br />
Tricalcium aluminate Concrete<br />
7. Calcium oxide (quick lime) is mixed with water.<br />
Ans. When calcium oxide reacts with vigorously with water to form calcium<br />
hydroxide(slaked lime). Since a large amount <strong>of</strong> energy is released, it is<br />
an exothermic reaction.<br />
SCHOOL SECTION 35
SCIENCE & TECHNOLOGY MT EDUCARE LTD.<br />
CaO (s) + H 2O (l) Ca(OH) 2 + Heat<br />
Calcium oxide Water Calcium hydroxide<br />
8. Potassium nitrate is mixed with water.<br />
Ans. When potassium nitrate is mixed with water, potassium nitrate dissolves<br />
in water. There is absorption <strong>of</strong> heat (endothermic reaction) and so the<br />
temperature <strong>of</strong> the solution falls.<br />
KNO 3(s) + H 2O (l) KNO 3(aq) + Heat<br />
Potassium nitrate Water Potassium nitrate<br />
9. Sodium hydroxide is mixed with water.<br />
Ans. When sodium hydroxide is mixed with water, sodium hydroxide dissolves<br />
in water. Since heat is liberated (exothermic), the temperature <strong>of</strong> the<br />
solution rises.<br />
NaOH (s) + H 2O (l) NaOH (aq) + Heat<br />
Sodium hydroxide Water Sodium hydroxide<br />
10.Glucose combines with oxygen during the process <strong>of</strong> respiration.<br />
Ans. When glucose combines with oxygen in the cells <strong>of</strong> our body during the<br />
process <strong>of</strong> respiration to form carbon-dioxide and water along with the<br />
production <strong>of</strong> energy.<br />
Since energy is released, it is an exothermic reaction.<br />
C 6H 12O 6(aq) + 6O 2(g) 6CO 2(g) + 6H 2O (l) + Energy<br />
Glucose Oxygen Carbon dioxide Water<br />
11.Calcium carbonate is heated.<br />
Ans. When calcium carbonate is heated, it decomposes to form calcium oxide<br />
(quick lime) and carbondioxide gas. As heat is absorbed, it is an endothermic<br />
reaction. Since the decomposition is brought by heat, it is also called as<br />
thermal decomposition.<br />
36<br />
CaCO 3(s)<br />
Heat<br />
CaO (s) + CO 2<br />
Calcium carbonate Calcium oxide Carbon dioxide<br />
1<strong>2.</strong>Sugar (sucrose) is heated strongly.<br />
Ans. When sucrose is heated strongly, it breaks down to give black coloured<br />
carbon and water. As heat is absorbed, it is an endothermic reaction.<br />
Since the decomposition is brought by heat, it is a thermal decomposition.<br />
C 12H 22O 11(s)<br />
Heat<br />
12C (s) + 11H 2O (g)<br />
Sugar Carbon Water<br />
13.Silver bromide is exposed to light.<br />
Ans. When silver bromide is exposed to light, yellow colour <strong>of</strong> silver bromide<br />
changes to grey colour.<br />
Silver bromide is decomposed to form grey silver metal and bromine gas is<br />
liberated.<br />
This reaction is used in black and white photography during the process <strong>of</strong><br />
developing.<br />
2AgBr (s)<br />
Sunlight<br />
2Ag (s) + Br 2(g)<br />
Silver bromide Silver metal Bromine gas<br />
14.Silver chloride is exposed to light.<br />
Ans. When silver chloride is exposed to light, white colour <strong>of</strong> silver chloride<br />
changes to grey colour.<br />
Silver bromide is decomposed to form grey silver metal and chloride gas is<br />
liberated.<br />
This reaction is used in black and white photography during the process <strong>of</strong><br />
developing.<br />
2AgCl (s)<br />
Sunlight<br />
2Ag (s) + Cl 2(g)<br />
Silver chloride Silver metal Bromine gas<br />
SCHOOL SECTION
MT EDUCARE LTD. SCIENCE & TECHNOLOGY<br />
15.Calcium sulphide reacts with dilute hydrochloric acid.<br />
Ans. When calcium sulphide reacts with dilute hydrochloric acid to give calcium<br />
chloride and hydrogen sulphide gas is liberated.<br />
CaS (s) + 2HCl (l) CaCl 2(s) + H 2S (g)<br />
Calcium sulphide Hydrochloric acid Calcium chloride Hydrogen sulphide<br />
16.Zinc reacts with copper sulphate.<br />
Ans. When zinc reacts with copper sulphate, zinc being more reactive than<br />
copper displaces copper to give colourless zinc sulphate and reddish brown<br />
deposit <strong>of</strong> copper. So, it is a displacement reaction. The blue colour <strong>of</strong><br />
copper sulphate fades due to formation <strong>of</strong> colourless zinc sulphate.<br />
CuSO 4(s) + Zn (s) ZnSO 4(aq) + Cu (s)<br />
Copper sulphate Zinc Zinc sulphate Copper<br />
17.Iron reacts with copper sulphate.<br />
Ans. When iron reacts with copper sulphate, iron being more reactive than<br />
copper displaces copper to give light green colored solution <strong>of</strong> iron sulphate<br />
and reddish brown deposit <strong>of</strong> copper. So, it is a displacement reaction. The<br />
blue colour <strong>of</strong> copper sulphate fades due to formation <strong>of</strong> light green solution<br />
<strong>of</strong> zinc sulphate.<br />
CuSO 4(s) + Fe (s) FeSO 4(aq) + Cu (s)<br />
Copper sulphate Iron Iron sulphate Copper<br />
18.Copper chloride reacts with potassium iodide.<br />
Ans. When copper chloride reacts with potassium iodide, it gives a brown coloured<br />
precipitate <strong>of</strong> cupric iodide and potassium chloride.<br />
This reaction is a double displacement reaction.<br />
2CuCl 2(aq) + 2KI (aq) CuI 2 + 2KCl<br />
Copper chloride Potassium iodide Cuppric iodide Potassium chloride<br />
19.Silver nitrate reacts with sodium chloride solution.<br />
Ans. When silver nitrate solution reacts with sodium chloride solution it gives a<br />
white precipitate <strong>of</strong> silver chloride and sodium nitrate.<br />
This reaction is a double displacement reaction.<br />
AgNO 3(aq) + NaCl (aq) AgCl + NaNO 3(aq)<br />
Silver nitrate Sodium chloride Silver chloride Sodium nitrate<br />
20.Barium sulphide reacts with zinc sulphate solution.<br />
Ans. When barium sulphate reacts with zinc sulphate solution, it gives a white<br />
precipitate <strong>of</strong> barium sulphate and zinc sulphide.<br />
This reaction is a double displacement reaction.<br />
BaS (aq) + ZnSO 4(aq) BaSO 4 + ZnS (aq)<br />
Barium sulphide Zinc sulphate Barium sulphate Zinc sulphide<br />
21.Aluminium is burnt in air.<br />
Ans. When aluminium is burnt in air, it gets oxidized to form aluminium oxide<br />
or alumina.<br />
4Al (s) + 3O 2(g) 2Al 2O 3(s)<br />
Aluminium oxygen Aluminium oxide<br />
2<strong>2.</strong>Sodium metal reacts with ethyl alcohol.<br />
Ans. When sodium metal reacts with ethyl alcohol to give sodium ethoxide and<br />
hydrogen gas is liberated. The hydrogen atom <strong>of</strong> the hydroxyl (OH)group is<br />
replaced by a sodium atom, forming sodium ethoxide.<br />
2C 2H 5OH (l) + 2Na (s) 2C 2H 5ONa (g) + H 2 <br />
Ethyl alcohol Sodium Sodium ethoxide Hydrogen<br />
SCHOOL SECTION 37
SCIENCE & TECHNOLOGY MT EDUCARE LTD.<br />
MEMORISE :<br />
Sodium ethoxide is a strong base. It is commercially available as a dry<br />
yellow solid, or as a solution in ethanol. – Extra Information.<br />
23.Hydrogen gas is passed over carbon.<br />
Ans. When hydrogen gas is passed over carbon, it gives methane.<br />
C (s) + 2H 2(g) CH 4(g)<br />
Carbon Hydrogen Methane<br />
24.Hydrogen gas is passed over copper oxide.<br />
Ans. When hydrogen gas is passed over copper oxide, it gives a pinkish brown<br />
coating <strong>of</strong> copper.<br />
CuO (s) + H 2(g) Cu (s) + H 2O (l)<br />
Copper oxide Hydrogen Copper Water<br />
25.Ozone is subjected to heat and light.<br />
Ans. When ozone is subjected to heat and light, it gives oxygen gas and nascent<br />
oxygen.<br />
38<br />
O3 Light, <br />
O2 + [O]<br />
Ozone Oxygen Nascent oxygen<br />
MEMORISE :<br />
Nascent oxygen is a single oxygen atom, a short-lived free radical <strong>of</strong> oxygen.<br />
Stratospheric ozone protects us from harmful ultra-violet radiation from<br />
the Sun. However, in the troposphere, ozone is dangerous to our health.<br />
Its not true that we don't want any ozone in the troposphere. We need low<br />
levels in the air to form hydroxyl radicals (OH) to clean the air <strong>of</strong> harmful<br />
chemicals. However, high concentrations <strong>of</strong> ozone are harmful to our<br />
health and damage plants. The highest levels <strong>of</strong> ozone in the atmosphere<br />
are in the stratosphere, in a region also known as the ozone layer between<br />
about 10 km and 50 km above the surface (or between about 6 and 31<br />
miles). Here it filters out photons with shorter wavelengths (less than<br />
320 nm) <strong>of</strong> ultraviolet light, also called UV rays, (270 to 400 nm) from the<br />
Sun that would be harmful to most forms <strong>of</strong> life in large doses.<br />
– Extra Information.<br />
26.Barium sulphate reacts with carbon.<br />
Ans. When barium sulphate reacts with carbon, barium sulphate gets reduced<br />
to barium sulphide and carbon gets oxidized to carbon monoxide.<br />
BaSO 4(aq) + 4C (s) BaS + 4CO (g)<br />
Barium sulphate Carbon Barium sulphide Carbon monoxide<br />
27.When an iron rod is exposed to air.<br />
Ans. When an iron rod is exposed to air, it gets oxidized by oxygen in air in the<br />
presence <strong>of</strong> moisture to form reddish brown coloured hydrated iron oxide.<br />
This process is called rusting <strong>of</strong> iron. The number <strong>of</strong> water molecules in<br />
the rust varies.<br />
4Fe (s) + 3O 2(g) + 2xH 2O (l) 2Fe 2O 3.xH 2O (s)<br />
Iron Oxygen Water Hydrated iron oxide<br />
28.Sodium hydroxide reacts with hydrochloric acid.<br />
Ans. When sodium hydroxide reacts with hydrochloric acid, it undergoes<br />
neutralization reaction to give sodium chloride and water.<br />
NaOH (aq) + HCl (aq) NaCl (aq) + H 2O (l)<br />
Sodium hydroxide Hydrochloric acid Sodium chloride Water<br />
Base Acid Salt<br />
SCHOOL SECTION
MT EDUCARE LTD. SCIENCE & TECHNOLOGY<br />
Positively charged radicals or<br />
basic radicals or cations<br />
Monovalent cations<br />
H + Hydrogen ion<br />
Na + Sodium ion<br />
K + Potassium ion<br />
Ag + Silver ion<br />
NH 4+ Ammonium ion<br />
Cu + Cuprous ion (I)<br />
Divalent cations<br />
Mg +2 Magnesium ion<br />
Ca +2 Calcium ion<br />
Cu +2 Cupric ion (II)<br />
Fe +2 Ferrous ion (II)<br />
Zn +2 Zinc iron<br />
Trivalent cations<br />
Al +3 Aluminium ion<br />
Fe +3 Ferric ion (III)<br />
Cr +3 chromium ion<br />
Negatively charged radicals or acidic<br />
radicals or anions<br />
F – Fluoride ion<br />
Cl – Chloride ion<br />
Br – Bromide ion<br />
I – Iodide ion<br />
OH – hydroxide ion<br />
HCO3 bicarbonate ion<br />
Divalent anions<br />
O –2 Oxide ion<br />
2<br />
CO3 Carbonate ion<br />
2<br />
SO4 sulphate ion<br />
S –2 sulphide ion<br />
Trivalent anions<br />
N –3 nitride ion<br />
3<br />
PO4 phosphate ion<br />
3<br />
BO4 borate ion<br />
SCHOOL SECTION 39
SCIENCE & TECHNOLOGY MT EDUCARE LTD.<br />
ACTIVITY : <strong>2.</strong>1<br />
40<br />
ACTIVITY BASED QUESTIONS<br />
Q. Take a table spoon full <strong>of</strong> copper powder in a china dish. Heat it strongly.<br />
What changes do you observe ?<br />
ACTIVITY : <strong>2.</strong>2<br />
Q. Take a small piece <strong>of</strong> aluminium wire and burn it. Record your<br />
observations. Remove a tungsten wire from a fused bulb. Try to ignite<br />
it. What do you observe ?<br />
ACTIVITY : <strong>2.</strong>3<br />
Q. Add potassium chromate (K 2CrO 4) to barium sulphate (BaSO 4) solution.<br />
Note your observations.<br />
ACTIVITY : <strong>2.</strong>4<br />
Q. Add a small quantity <strong>of</strong> dil.H 2SO 4 to FeS very carefully, (under supervision<br />
<strong>of</strong> your teacher). Touch the test tube. Also experience the odour. What<br />
do you observe ?<br />
ACTIVITY : <strong>2.</strong>5<br />
Q. Heat camphor in a porcelain dish. Keep a funnel plugged with cotton<br />
over the dish before you heat. What do you observe when camphor<br />
burns ? What happens when the apparatus is cooled ?<br />
Complete the table with reference to the activities (<strong>2.</strong>1 to <strong>2.</strong>5).<br />
Ans.<br />
Activity<br />
<strong>2.</strong>1<br />
<strong>2.</strong>2<br />
<strong>2.</strong>3<br />
<strong>2.</strong>4<br />
<strong>2.</strong>5<br />
ACTIVITY : <strong>2.</strong>6<br />
Change in<br />
colour<br />
Black<br />
Black<br />
Black<br />
Substances<br />
Sublime<br />
Evolution <strong>of</strong><br />
gas<br />
Q. Take a small piece <strong>of</strong> used paper. Weight it on an electronic balance<br />
which will be readily available in your nearby grocery shop. Burn the<br />
piece <strong>of</strong> paper and now weigh the ash. What do you observe about the<br />
initial and final weighs? What can you infer ?<br />
Ans. Suppose the weight <strong>of</strong> small piece <strong>of</strong> used paper is 2 gms. After burning the<br />
piece <strong>of</strong> paper the weight <strong>of</strong> ash remains the same i.e. 2 gms.<br />
So, we observe that the weight remains the same. This is due to law <strong>of</strong><br />
conservation <strong>of</strong> mass.<br />
Yes<br />
Yes<br />
Hydrogen<br />
sulphide<br />
Black<br />
Carbon smoke<br />
Change in<br />
temperature<br />
Yes<br />
Yes<br />
No<br />
Yes<br />
Change in<br />
state<br />
No<br />
Comparous<br />
powder<br />
Yes<br />
Yes<br />
SCHOOL SECTION
MT EDUCARE LTD. SCIENCE & TECHNOLOGY<br />
The total mass <strong>of</strong> the reactant is equal to the total mass <strong>of</strong> the products<br />
during a chemical reaction. Therefore chemical equation needs to be balanced.<br />
ACTIVITY : <strong>2.</strong>6<br />
Q. Rehana and Reshma were having fun with colours in their drawing<br />
class. Rehana mixed few drops <strong>of</strong> red colour with white colour and got<br />
pink colour. Reshma mixed yellow with red colour to get orange shade.<br />
They also prepared violet by mixing red and blue and grey by mixing<br />
black and white colours. When you mix “VIBGYOR” colours, what colour<br />
do you get ?<br />
Ans. When VIBGYOR colours are mixed you get one colour that is white if the<br />
colours are faint as in rainbow.<br />
ACTIVITY : <strong>2.</strong>8<br />
Q. Take a small quantity <strong>of</strong> detergent powder or washing soda in your<br />
hand and add a little water to it. What do you feel ? Is there any change<br />
in temperature when water is added to detergent ?<br />
Ans. When we add water to detergent powder or washing soda in our hands, it is<br />
slippery to touch. Yes, there is change in temperature, temperature increases.<br />
ACTIVITY : <strong>2.</strong>9<br />
Q. Take 100 ml <strong>of</strong> distilled water in two polythene bottles. (This prevent<br />
heat loss.) Note the temperature <strong>of</strong> water in both bottles. Add about 5<br />
gm <strong>of</strong> potassium nitrate (KNO 3) to one bottle stir well. Note temperature<br />
<strong>of</strong> the solution. Add 5 gm <strong>of</strong> NaOH to the other bottle. Note the solution<br />
temperature. What do you observe in both the cases ? What inferences<br />
can you draw ?<br />
Ans. At the start, temperature <strong>of</strong> distilled water in two bottles was suppose<br />
60ºC. When we add KNO 3 to one <strong>of</strong> the bottles, temperature <strong>of</strong> solution<br />
falls down to 50ºC, this is because there is absorption <strong>of</strong> heat during the<br />
reaction.<br />
When we add NaOH to other bottle, there is rise in temperature as there<br />
is evolution <strong>of</strong> heat during this reaction.<br />
ACTIVITY : <strong>2.</strong>10<br />
Q. Marry was helping her mother to make brown sugar for pudding. After<br />
sometime she obtained a black mass instead <strong>of</strong> brown with burning<br />
smell. What do you think might have happened ?<br />
Ans. Brown sugar is made by heating the sugar, but due to excessive heating<br />
the sugar burnt to form black coloured carbon.<br />
ACTIVITY : <strong>2.</strong>11<br />
Q. Take a spatula full <strong>of</strong> silver bromide (Your teacher will help you get it.)<br />
on a watch glass. Note its colour. Place the watch glass in sunlight.<br />
Observe the colour after some time.<br />
Ans. When we take silver bromide on a watch glass its colour is pale yellow.<br />
When we place this watch glass in sunlight the colour <strong>of</strong> silver bromide<br />
turns grey.<br />
SCHOOL SECTION 41
SCIENCE & TECHNOLOGY MT EDUCARE LTD.<br />
ACTIVITY : <strong>2.</strong>12<br />
Q. Take two completely used cells out <strong>of</strong> a wall clock, transistor, tape<br />
recorder, etc. Remove the material from inside. You will get a can that<br />
is made <strong>of</strong> zinc. Press and make it flat. Dip the zinc strip in copper<br />
sulphate solution (A). Let there be copper sulphate solution in another<br />
beaker B for comparison. Keep another plain zinc strip also for<br />
comparison. Remove the zinc strip after about 5 minutes. Compare<br />
1. Intensity <strong>of</strong> blue colour <strong>of</strong> CuSO 4 in beaker A and beaker B.<br />
<strong>2.</strong> The colour <strong>of</strong> the zinc strips.<br />
Ans. 1. Intensity <strong>of</strong> blue colour <strong>of</strong> CuSO 4 in beaker A fades away and intensity<br />
<strong>of</strong> blue colour <strong>of</strong> CuSO 4 in beaker B remains the same.<br />
<strong>2.</strong> The colour <strong>of</strong> the zinc strip turns brown.<br />
ACTIVITY : <strong>2.</strong>14<br />
Q. During festivals all <strong>of</strong> you have fun while bursting crackers. When<br />
crackers burn, you will find an ash residue after they are burnt. What<br />
reaction has taken place ?<br />
Ans. The reaction which has taken place while burning crackers is oxidation<br />
reaction. Crackers are made up <strong>of</strong> phosphorus and magnesium powder<br />
which gives the sparkling light. On burning they form an ash consisting <strong>of</strong><br />
oxides P 4O 10, MgO and Mg 3N <strong>2.</strong><br />
ACTIVITY : <strong>2.</strong>15<br />
Q. Have you ever peeped into the store room <strong>of</strong> your home ? If you have,<br />
you must have seen some old and out <strong>of</strong> use articles made <strong>of</strong> iron. They<br />
are usually covered with a reddish layer. Do you know what red layer is<br />
called ?<br />
Ans. The reddish brown colour is deposited over the surface <strong>of</strong> iron is because<br />
<strong>of</strong> oxidation i.e. formation <strong>of</strong> Fe 2O 3.H 2O.<br />
ACTIVITY : <strong>2.</strong>16<br />
Q. After you have your dinner tonight, wash your own plate with soap/<br />
detergent. What colour change is observed when soap/detergent is<br />
applied ? Can you name the type <strong>of</strong> reaction ?<br />
Ans. The yellow oily left over stains turn red/orange because <strong>of</strong> neutralization.<br />
42<br />
SCHOOL SECTION
MT EDUCARE LTD. SCIENCE & TECHNOLOGY<br />
QUESTIONS & ANSWERS (TEXBOOK PAGE NO. 13)<br />
1. (a) Name the reactants and products in equation.<br />
dil.HCl<br />
C12H22O 11(s) + H2O <br />
(aq) 323 K, alcoholic<br />
Ans. In the given reaction :<br />
Reactants : C 12H 22O 11(s) + H 2O (aq)<br />
(Sugar) Water<br />
Products : C 6H 12O 6(s) + C 6H 12O 6(s)<br />
Glucose Fructose<br />
(b) What is the name <strong>of</strong> the process in equation ?<br />
n(H 2C = CH 2)<br />
high temp. ( )<br />
<br />
high pressure<br />
<br />
<br />
H H<br />
<br />
| | <br />
C C <br />
| | <br />
<br />
H H<br />
<br />
<br />
<br />
<br />
n<br />
Ethylene Polyethylene<br />
Ans. The name <strong>of</strong> the process is POLYMERIZATION.<br />
QUESTIONS & ANSWERS (TEXBOOK PAGE NO. 16)<br />
C 6H 12O 6 + C 6H 12O 6<br />
1. Paste <strong>of</strong> substance ‘A’ is used to decorate the ceiling <strong>of</strong> your home.<br />
(a) Name the substance A and write its formula.<br />
(b) Write the reaction <strong>of</strong> substance A with H 2O. State the name <strong>of</strong> the<br />
product (B).<br />
(c) Where and how is ‘B’ useful ?<br />
Ans. (a) The substance A is plaster <strong>of</strong> Paris and its formula is 2 CaSO 4.H 2O.<br />
(b) The reaction <strong>of</strong> A with H 2O is<br />
2CaSO 4.H 2O + 3H 2O 2CaSO 4.2H 2O<br />
Plaster <strong>of</strong> Paris Gypsum (B) + Heat<br />
(c) Gypsum is the raw material used in manufacturing cement.<br />
<strong>2.</strong> Will it be possible for you to decompose water by heat or light energy ?<br />
If you pass current from a 6 volt battery is decomposition <strong>of</strong> water<br />
possible ?<br />
Ans. If you take pure water it is not possible to decompose water by heat or light<br />
energy or using a 6 volt battery. But if you add a few drops <strong>of</strong> acid to water<br />
then it is possible to decompose acidulated water by passing current from<br />
a 6 volt battery.<br />
QUESTIONS & ANSWERS (TEXBOOK PAGE NO. 19)<br />
1. When copper articles are exposed to light and moisture. Do they undergo<br />
corrosion ?<br />
Ans. Copper oxidises to form black copper oxide. Further copper oxide slowly<br />
reacts with CO 2 in air to form copper carbonate which is green in colour.<br />
Thus, copper articles are exposed to light and moisture, they undergo<br />
corrosion to form the green coating on its surface.<br />
SCHOOL SECTION 43
SCIENCE & TECHNOLOGY MT EDUCARE LTD.<br />
<strong>2.</strong> What happens to silver ornaments ?<br />
Ans. Exposure to light has no action on silver ornaments. But if the air is<br />
contaminated with H 2S, the silver is blackened due to the formation <strong>of</strong> a<br />
thin film <strong>of</strong> black silver sulphide (Ag 2S) on the surface. Thus, black coating<br />
is formed on silver ornaments.<br />
3. What according to you is the reason for aluminium utensils regaining<br />
their original shine when green leafy vegetables are boiled in them ?<br />
Ans. Aluminium utensils become dull after a long time due to oxidation <strong>of</strong> Al to<br />
Aluminium oxide (Al 2O 3). Leafy vegetables contain chlorophyll and<br />
chlorophyll has a capacity to produce reducing agent. When leafy vegetables<br />
are boiled in dull aluminium utensils, Al 2O 3 is reduced to Al and thus<br />
regain their original shine.<br />
4. Visit an oil merchant, request him to give you 100 ml <strong>of</strong> left over edible<br />
oil from the tin. Heat it in a container. Note your observation.<br />
Ans. When leftover edible oil is heated, it undergoes oxidation and starts frothing<br />
up and its smell turns foul.<br />
5. Find out the names <strong>of</strong> some natural antioxidants. Now a days many<br />
antioxidants are available in pharmacies. Can you list some brand<br />
names ?<br />
Ans. Antioxidants are the compounds which prevent the oxidation or deterioration<br />
<strong>of</strong> food. Naturally occurring many fruits contain antioxidants such as apple,<br />
strawberry, etc., dry fruits like walnut, almonds, etc., vegetable like<br />
capsicum, papaya, tomato, carrots, etc. -carotene and lycopene are natural<br />
antioxidants.<br />
Many antioxidants are available in pharmacies which contain BHA<br />
(Butylated hydroxy anisole), BHT (Butylated hydroxy toluene).<br />
6. Kurkure, chips, fryums, etc. are stored in air tight containers. Is that<br />
enough to prevent oxidation ?<br />
Ans. No. It helps to slow down oxidation.<br />
7. What more steps are taken to prevent oxidation <strong>of</strong> edible articles ?<br />
Ans. To prevent oxidation <strong>of</strong> the edible articles, the bags used to wrap the edible<br />
articles are flushed with an inert gas such as nitrogen.<br />
44<br />
SCHOOL SECTION
MT EDUCARE LTD. SCIENCE & TECHNOLOGY<br />
HOTS QUESTIONS & ANSWERS<br />
1. Meena and Rakesh cleaned utensils used for cooking with the help <strong>of</strong><br />
ash and soap respectively. Who must have got the best results ? Why ?<br />
Ans. Rakesh must have got the best results after cleaning the utensils by scap.<br />
Edible oils are used while cooking. They are organic compounds made up<br />
<strong>of</strong> alcohols and carboxylic acids. They are neutralized by alkaline soaps.<br />
Ash cannot bring this kind <strong>of</strong> result.<br />
<strong>2.</strong> When washing soda is rubbed on wet palms warmness is experienced.<br />
Is the reaction exothermic or enothermic ? Why ?<br />
Ans. When washing soda dissolves in water there is evolution <strong>of</strong> heat which we<br />
feel on our palm, it is exothermic reaction.<br />
3. Imagine you are preparing halwa for the first time and you forget to<br />
turn <strong>of</strong>f the gas after the preparation was over. What would happen ?<br />
Why ?<br />
Ans. The sugar in the halwa get overheated and breakdown to give a simple<br />
product C + H 2 O. The halwa would turn in to black mass with burning<br />
smell.<br />
4. When copper articles are exposed to light and moisture. Do they undergo<br />
corrosion ?<br />
Ans. (a) Copper oxidises to form black copper oxide.<br />
(b) Further copper oxide slowly reacts with CO 2 in air to form copper<br />
carbonate which is green in colour.<br />
(c) Thus, copper articles are exposed to light and moisture. They undergo<br />
corrosion to form the green coating on its surface.<br />
SCHOOL SECTION 45
SCIENCE & TECHNOLOGY MT EDUCARE LTD.<br />
46<br />
GLOSSARY<br />
Galvanizing : Process <strong>of</strong> depositing a thin layer <strong>of</strong> zinc metal on iron<br />
objects to prevent corrosion.<br />
Electro-plating : Electroplating is a plating process in which metal ions in a<br />
solution are moved by an electric field to coat an electrode.<br />
Ester : Esters are usually derived from an inorganic acid or organic<br />
acid in which at least one -OH (hydroxyl) group is replaced<br />
by an -O-alkyl (alkoxy) group, and most commonly from<br />
carboxylic acids and alcohols.<br />
Carboxylic acid : Carboxylic acids are organic acids characterized by the<br />
presence <strong>of</strong> at least one carboxyl group. The general formula<br />
<strong>of</strong> a carboxylic acid is R-COOH, where R is some monovalent<br />
functional group.<br />
Alcohol : In chemistry, an alcohol is any organic compound in which<br />
a hydroxyl functional group (-OH) is bound to a carbon<br />
atom, usually connected to other carbon or hydrogen atoms.<br />
Gravel : Gravel is a rock that is <strong>of</strong> a specific particle size range.<br />
Specifically, it is any loose rock that is larger than 2 mm<br />
(0.079 in) in its smallest dimension (about 1/12 <strong>of</strong> an inch)<br />
and no more than 64 mm (<strong>2.</strong>5 in).<br />
Sago : Sago is a starch extracted from the pith <strong>of</strong> sago palm stems.<br />
Precipitate : Solid insoluble substance sometimes produced when 2<br />
solutions are mixed or a gas is passed into a solution<br />
Nascent oxygen : It is a single oxygen atom, a short-lived free radical <strong>of</strong><br />
oxygen.<br />
Catalyst : A substance whose mere presence affects the rate <strong>of</strong><br />
chemical reaction without undergoing itself any chemical<br />
change.<br />
Aqueous solution : Solution in which solvent is water.<br />
Voltameter : A scientific instrument used for measuring quantity <strong>of</strong><br />
electricity. It should not be confused with a voltmeter which<br />
measures electric potential. An alternative name is<br />
coulometer.<br />
Ions : An atom or molecule in which the total number <strong>of</strong> electrons<br />
is not equal to the total number <strong>of</strong> protons, giving it a net<br />
positive or negative electrical charge.<br />
Oxidizing agent : The substance that gives oxygen or removes hydrogen for<br />
oxidation.<br />
Reducing agent : The substance that gives hydrogen or removes oxygen for<br />
reduction.<br />
Formula : Symbolic representation <strong>of</strong> molecule <strong>of</strong> a substance.<br />
Symbol : Abbreviation <strong>of</strong> full name <strong>of</strong> an element.<br />
AMAZING FACTS<br />
Each time lightning strikes, some Ozone gas is produced, thus<br />
strengthening the Ozone Layer in the Earth's atmosphere.<br />
Hot water freezes faster than cold water (the Mpemba effect).<br />
<br />
SCHOOL SECTION
S.S.C.<br />
SCIENCE<br />
CHAPTER 2 : MAGIC OF CHEMICAL REACTIONS<br />
Marks : 30<br />
Duration : 1 hr.<br />
Q.I [A] Fill in the blanks : 2<br />
1. The chemical reaction during which hydrogen is lost is called as<br />
....................... .<br />
<strong>2.</strong> The chemical reaction in which heat is evolved is called as<br />
....................... reaction.<br />
3. Products are represented on ....................... .<br />
4. When copper powder is heated, ....................... is formed.<br />
Q.I [B] Match the columns : 2<br />
Column A Column B<br />
1. Gain <strong>of</strong> oxygen (a) <strong>Chemical</strong> change<br />
<strong>2.</strong> Digestion (b) Oxidation<br />
3. Iodine, Camphor (c) Balanced equation<br />
4. NaOH + HCl NaCl + H 2O (d) Sublimatory substances<br />
Q.I [C] State whether True or False : 1<br />
1. Conversion <strong>of</strong> quick lime to slaked lime is an example <strong>of</strong> displacement<br />
reaction.<br />
<strong>2.</strong> <strong>Chemical</strong> change is a temporary change.<br />
Q.I [D] Find odd man out : 1<br />
1. , (g), (l), =.<br />
<strong>2.</strong> Conversion <strong>of</strong> milk to curd, Rusting <strong>of</strong> iron, Digestion <strong>of</strong> food, Water<br />
turns into ice.<br />
Q.II [A] Give scientific reasons : (Any Two) 4<br />
1. Grills <strong>of</strong> doors and windows are always painted before they are<br />
used.<br />
<strong>2.</strong> Edible oil is not allowed to stand for a long time in an iron or tin<br />
container.<br />
3. Conversion <strong>of</strong> ice into water is a physical change.<br />
Q.II [B] Distinguish between : 2<br />
1. Physical change and <strong>Chemical</strong> change.
... 2 ...<br />
Q.III [A] Balance the following chemical reaction : (Any Three) 3<br />
1. S + H 2 SO 4 H 2 O + SO 2<br />
<strong>2.</strong> NH 4 Cl + Ca(OH) 2 CaCl 2 + H 2 O + NH 3<br />
3. Fe 2 O 3 + CO Fe + CO 2<br />
4. ZnS + O 2 ZnO + SO 2<br />
Q.III [B] Identify the following reaction : 3<br />
1. 2HgO <br />
Heat 2Hg + O2 <br />
<strong>2.</strong><br />
3.<br />
CuSO + Fe FeSO + Cu<br />
4 4<br />
CaO + H O Ca(OH) + heat<br />
2 2<br />
Q.IV Explain the following chemical reactions with the help <strong>of</strong> 6<br />
balanced equation : (Any Three)<br />
1. Calcium carbonate is heated.<br />
<strong>2.</strong> Silver bromide is exposed to light.<br />
3. Iron reacts with copper sulphate.<br />
4. Silver nitrate reacts with sodium chloride solution.<br />
Q.V [A] Answer the following in detail : (Any One) 4<br />
1. What is the importance <strong>of</strong> a chemical equation? OR<br />
What information is conveyed by a chemical equation, give an<br />
example.<br />
<strong>2.</strong> State the neutralization.<br />
Q.V [B] Define the following : 2<br />
1. Redox reaction.<br />
<strong>2.</strong> Corrosion.<br />
Best Of Luck