Acid/Base Titrations

EXPERIMENT 3
Using Dilution Factors In An Acid –Base Titration& Analysis Of
Vinegar
Aim :
1. To prepare diluted solutions of more concentrated solution.
2. To determine an unknown concentration of Sodium
hydroxide solution
3. To determine the concentration of acetic acid in vinegar .

Introduction
•When acids and bases are added together a neutralization reaction
takes place. An acid and a base combine to produce water and salt.
For example:
Hydrochloric acid + Sodium hydroxide
HCl + NaOH HOH + NaCl
water + salt
The acid donates a proton (H+) to the hydroxide (OH-) of the base
to form water.

Titration method
• Unknown amount of Base add to acid for
titration.
• Using buret – flask titration until the end
point.
• Report the volume used.

Indicators
• Phenolphthalein
• Methyl Red
• Methyl orange
Few drops to be used
To see the colour change of the solutions to
show the end point .

Procedure :
A-Dilution:
1- Diluted HCl :
Pipette 4.0 ml of the stock 1.00M HCl into 100.0ml v.flask
Add distilled water to the mark100.0 ml
M 1 X V 1 = M 2 X V 2
1.00M X 4.0 ml = M 2 X 100.0ml M 2 = 0.04 mol / L

2- Diluted NaOH :
Pipette 10.0 ml of stock (concentrated) sodium hydroxide into 100.0 ml
v.flask. Add distilled water to the mark 100.0 ml

B-Titration of HCl & NaOH:
1-Fill the burette with diluted NaOH Solution. Be certain to
open the stopcock and allow a few ml to flow out.
2-Record the initial volume of NaOH.

3-Measure 10.0 ml of diluted HCl in a conical flask using a
pipette.
.

4- Add 2 to 3 drops of phenolphthalein to the HCl solution and
swirl it thoroughly.

5-Stop the titration when the first appearance of pink colour
is observed.

6-Record final volume of the burette.
7-Repeat the titration steps three times.

C.Analysis of vinegar:
1-Pipette 5.0ml of stock vinegar solution into a 100.0ml volumetric flask.
Add distilled water to make 100.0 ml and mix the solution.

2-Pipette 10.0 ml of diluted vinegar solution to a 250.0 ml conical
flask.

3- Add 2-3 drops of phenolphthalein to the vinegar solution.

4-Titrate the vinegar solution with the same NaOH solution used
before.

5-Stop the titration when when the first appearance of pink colour is
observed.

6-Record the final volume of the burette.
7-Repeat the titration steps three times.

Q-1 What is the unit of volume on a
burette?
Q-2 What is the maximum volume
that can be measured with our
burettes?

• Gently pull the tip off and rinse it out also.

How to use the burette properly
• The burette with the red dot must be used for
acids and the burette with the blue dot must be
used for bases.
• Fill your burettes to approximately 30 mL. Be sure
there are no air bubbles in the tip of your burette.
Record your beginning volumes on your paper.
• To read the meniscus you must be at eye level,
and read at the bottom line of the dip.

• Holding a white card with a black line
behind the burette can be very helpful
•Each line on our burette represents 1/10 of a mL so
be sure to estimate your readings to .01 mL

Q-3 What is the reading here?

• To release liquid turn, the stopcock. Be
careful to not pull out on the stopcock as
you turn it.

In a titration with this ratio we can use the
following relationship
M a x V a = M b x V b
molarity of acid x volume of acid = molarity of base x volume of base

In titration, one of the solution is standard
solution, which has know concentration.
From the measured volume of the other
solution by titration, the concentration of the
second solution can be calculated.

• The indicator phenolphthalein is used to
tell when the acid and base exactly
neutralize each other. This is called the
endpoint of the titration.
• When phenolphthalein is added to an acid
it remains clear. When it is added to a base
it turns pink

• As liquid is added to the Erlenmeyer flask
always swirl gently

• The endpoint of a titration is shown by a
light pink color that stays for at least 30
seconds

• Record the beginning volumes of acid and base. Also record the molarity of the acid.
• Add approximately 10 ml of acid to the flask and begin to add base.
• The first time through a titration we add the base quickly to turn the solution pink. You can
then a small amount of acid and then titrate to the light pink endpoint.

• When you are close to the endpoint you
often need to add very small amounts of
acid or base. To do this, turn the stopcock
just enough to have 1 small drop of liquid
hanging from the bottom of the buret.

• The key to a successful titration is patience!
• Always use clean equipment
• Remember to record your beginning and ending volumes and read to .01 mL
• Read the meniscus correctly
• Use the formula M a x V a = M b x V b for a 1:1 mole ratio to calculate the concentration of your unknown solution
Good Luck