The Mole

Chapter 7

Chemical Quantities

Determine the percent composition of Fe(OH)2

Fe – 1 x 55.8 = 55.8

O – 2 x 16 = 32

H – 2 x 1 = 2

Molar mass = 89.8

Divide element mass by molar mass, then multiply by 100.

Fe –55.8 x 100

89.8

O – 32 x 100

89.8

Divide element mass by molar mass, then multiply by 100.

H –2 x 100

89.8

Percent compositions

% composition Fe = 62.1%

% composition 0 = 35.6%

% composition Fe = 2.2%

Add them up. Do they total 100?

Empirical formulas

Which of the following are empirical formulas?

HCl

K2C2O4

Pb2O4

Empirical formulas

Only one is an empirical formula.

HCl

The subscripts cannot be reduced.

Find the number of molecules in 24 g of CO

24 g (1 mole)

( 28 g )

= 0.86 moles of CO

Find the number of molecules in 24 g of CO

0.86 mol (6.02 x 1023)

(1 mol)

5.2 x 1023

molecules of CO

Find the density of one mole of CO gas at STP.

Density = Mass divided by volume

D = 28 g = 1. 25 g/L

22.4 L

What is Avogadro’s number?

6.02 x 1023

units of a substance

What is the difference between molecular

mass and molar mass?

Molecular mass is in atomic mass units; molar mass is in grams.

What is the difference between a 6 M solution of

H2SO4 and a 1 M solution of H2SO4 ?

The 6 M (molar) sulfuric acid is much stronger. It has 6 moles of the acid dissolved in 1 liter of solution. The 1 M has 1 mole dissolved in 1 liter.

Convert 872 g of ammonium oxide

into moles.First find the correct formula for ammonium oxide.

(NH4)2O

Find the molar mass of ammonium oxide

(NH4)2O

N – 2 x 14 = 28

H – 8 x 1 = 8

O – 1 x 16 = 16

Find the molar mass of ammonium oxide

(NH4)2O = 52 grams

Set up a conversion factor to change from 872 g to moles.

Conversion factor

872 g ( 1 mol)

52 g

= 16.8