The Mole ConceptThe Mole Concept

Chapter 9

CHM 130

GCC

9.1 Avogadro’s Number and The Mole

Eggs come in dozens = convenient

12 = dozenAtoms come in moles

6.02 x 1023 = mole = NA

NA is just a super large number

The MoleThe Mole One mole of softballs would be the size of the Earth! But atoms are so tiny that one mole of atoms is

about a handful. The mass of a mole of atoms = the atomic mass in

grams in the Periodic Table1 mole of C atoms is 12.01 grams1 mole of Na atoms is 22.99 grams

sulfur

water

mercury

sodium chloride

copper

lead

sugar

Mole Examples

1. How many calcium atoms are in 0.250 moles of calcium:

2. Calculate the moles of 3.75 x 1027 molecules of oxygen gas:

9.2 Avogadro’s number :

6.02 x 1023 atoms or mlcls or 1 mol 1 mol 6.02 x 1023atoms or mlcls

0.250 mol Ca (6.02 x 1023 atoms/mol) = 1.51 x 1023 Ca atoms

3.75 x 1027 mlcls O2 ( mol/6.02 x 1023 mlcls) = 6230 mol O2

Periodic Table masses are in ( g /mol )

How many grams in one mole of

carbon?

gold?

sodium?

Note = these are all 6.02 x 1023 atoms!

9.3 Molar Mass:

12.01 g/mol

196.97 g/mol

22.99 g/mol

Calculate the molar mass of barium

hydroxide.

1.What is the formula?

2.Add up the mass for every atom.

Molar Mass:

Ba(OH)2

137.33 + 2 ( 16.00) + 2 ( 1.01 ) = 171.35 g / mol

Very important – the units are grams per 1 mole, not just grams

9.4 Grams to Moles & Vice Versa9.4 Grams to Moles & Vice Versa

Use Molar Mass as (g / mol) or (mol / g) How many grams is 1.667 moles of oxygen gas? How many moles is 45 grams of silver? How many grams is 0.0554 moles of water?

1.667 mol O2 ( 32.00 g/mol) = 53.34 g O2

45 g Ag ( mol/ 107.87 g) = 0.42 mol Ag

0.0554 mol H2O (18.02g /mol) = 0.998 g H2O

9.5 Molar Volume (V of 1 mole at STP)

Volume of 1 mole of gasVolume of 1 mole of gas

Gases are mostly empty space so they ALL have the same volume despite different mass

22.4 L per 1 mole of any gas at STP STP is Standard Temperature and Pressure

0°C and 1 atm

For Gases only at STP: 22.4 L / 1 mol or 1 mol / 22.4 L

What is the mass of 4.50 L of chlorine gas at STP?

4.50 L Cl2 (mol / 22.4L) (70.90 g/mol) = 14.2 g Cl2

What is the volume of 1.25 moles of gas at STP?

1.25 mol ( 22.4 L / 1 mol) = 28.0 L gas

DensityDensity

d = = memolar volu

massmolar

volume

mass

Calculate the density of ammonia gas, NH3, at STP.

d = (17.04 g/mol ) / ( 22.4 L/mol ) = 0.761 g/L

9.6 Mole Calcs

ExampleExample

How many grams does 17.35 liters of neon gas mass at STP? How many atoms is this?

17.35 L = 15.6 grams Ne

mol 1

g 20.18

L 22.4

mol 1

mol 1

atoms10 x 6.02

L 22.4

mol 1 23

17.35 L = 4.66x1023 atoms Ne

Percent CompositionPercent Composition = mass % of each element in a compound Water is basically 11% H and 89% O You divide the total element molar mass by the total

compound molar mass. %H = (2.02 g H / 18.02 g H2O) x 100 = 11.2% H %O = (16.00 g O / 18.02 g H2O) x 100 = 88.79% O Note the %’s should add up to 100% total

Example ProblemExample Problem Find the percent composition for TNT, C7H5(NO2)3

Total molar mass is 227.15 grams per mole

% C = (84.07g / 227.15g) x 100 = 37.01% C% H = (5.05g / 227.15g) x 100 = 2.22%H% N = (42.03g / 227.15g) x 100 = 18.50%N% O = (96.00g / 227.15g) x 100 = 42.26%O

Try at homeTry at home How many liters will 3.425 grams of carbon dioxide

gas occupy at STP? 1.74 L How many molecules are in 3.425 grams of carbon

dioxide? 4.68 x 1022 molecules How many grams will 3.0 x 1015 molecules of carbon

dioxide mass? 2.2 x 10-7 grams

Self TestSelf Test

Page 258 Try 1-7, 10-13 Answers in Appendix J