The Mole

Molar Rela)onships Unit 3 Chapter 3

Rela)ng Mass to Numbers of Atoms The Mole • A mole (symbol: mol) is the amount of a substance that contains as many par)cles as there are atoms in exactly 12 g of carbon-­‐12.

Dozen (12)Gross (144)Ream of paper (500)Mole (mol) of particles:(6.022 x 10 23 )

How Big is a Mole? One mole of marbles would cover the en)re Earth (oceans included) for a depth of three miles. One mole of $100 bills stacked one on top of another would reach from the Sun to Pluto and back 7.5 million )mes.

The Mole * in the 1800's, an Italian scien)st by the name of Amadeo Avogadro mathema)cally determined a way of conver)ng amu to grams. * Avogadro determined that when you had a mole of atoms of any element you would have the atomic mass of that element in grams; in other words, a mole of Carbon atoms has a mass of 12g.

Avogadro’s Number • Avogadros number: 6.022 1415 × 10 23 Amedeo Avogadro-­‐ Italian Chemist • the number of par)cles in exactly one mole of a pure substance.

Molar Mass • The mass of one mole of a pure substance is called the molar mass of that substance. • Molar mass is usually wri]en in units of g/mol. One mole of copper: 63.55 g/mol

Molar Mass • The molar mass of an element is numerically equal to the average atomic mass of the element in atomic mass units.

Molecular Weight and Molar Mass Formula mass The sum of average atomic masses of all atoms in the molecule or formula unit. example: NaCl has a formula mass of 58.5 a.m.u. This is a single unit of NaCl. Molar mass = mass in grams per mole. example: NaCl has a molar mass of 58.5 grams This is 6.02 x10 23 formula units of NaCl.

The Molar Mass and Number of Particles in One-MoleQuantitiesSubstance Molar Mass Number of Particles in One MoleCarbon (C) 12.0 g 6.02 x 10 23 C atoms Sodium (Na) 23.0 g 6.02 x 10 23 Na atoms Iron (Fe) 55.9 g 6.02 x 10 23 Fe atoms NaF (preventa)ve 42.0 g 6.02 x 10 23 NaF formula units for dental cavi)es) CaCO 3 (antacid) 100.1 g 6.02 x 10 23 CaCO 3 formula units C 6 H 12 O 6 (glucose) 180.0 g 6.02 x 10 23 glucose molecules C 8 H 10 N 4 O 2 (caffeine)194.0 g 6.02 x 10 23 caffeine molecules

Gram/Mole Conversions • Chemists use molar mass as a conversion factor in chemical calcula)ons. • For example, the molar mass of helium is 4.00 g He/mol He. • To find how many grams of helium there are in two moles of helium, mul)ply by the molar mass. 4.00 g He2.00 mol He != 8.00 g He1 mol He

Sample Problem What is the mass in grams of 3.50 mol of the element copper, Cu? Set up the problem with the appropriate conversion factor: moles Cu !grams Cumoles Cu= grams Cu

The molar mass of copper from the periodic table is rounded to 63.55 g/mol. 3.50 mol Cu !63.55 g Cu= 222 g Cu1 mol Cu

Avogadros number • Avogadro’s number can also be used to find the number of atoms of an element from the amount in moles • or to find the amount of an element in moles from the number of atoms. Avogadro’s number is expressed in units of par)cles per mole.

One More: How many moles of silver, Ag, are in 3.01 × 10 23 atoms of silver? Ag atoms!moles AgAvogadro's number of Ag atoms= moles Ag233.01 10 Ag atoms! !0.5001 mol Ag236.022 ! 10 Ag atm ol Agoms=

Cu atomsReally Just One more: What is the mass in grams of 1.20 × 10 8 atoms of copper, Cu? moles Cu! !Avogadro's number of Cu atomsgrams Cumoles Cu= grams CuThe molar mass of copper from the periodic table is rounded to 63.55 g/mol. 1 mol Cu 63.55 g Cu6.022!10 Cu atoms 1 mol Cu81.20! 10 Cu atoms ! !=23– 141.27!10 g CuEnd

Now let’s work some different types of problems using moles.