Everything Science Grade 10

19.2 CHAPTER 19. QUANTITATIVE ASPECTS OF CHEMICAL CHANGE

Step 2:Find the moles of oxygen

n=Mm

Lead

n=^207 g

207 , 2 g·mol−^1

= 1mol

Oxygen

n=^32 g

16 , 0 g·mol−^1

= 2mol

Step 3:Find the mole ratio

The mole ratio of Pb:O in the product is1 : 2, which means that for

every atom of lead, there will be two atoms of oxygen. The formula of

the compound is PbO 2.

Example 10: Empirical and molecular formula

QUESTION

Vinegar, which is used in our homes, is a dilute form of acetic acid. A sample

of acetic acid has the following percentage composition: 39 ,9%carbon, 6 ,7%

hydrogen and 53 ,4%oxygen.

1. Determine the empirical formula of acetic acid.

2. Determine the molecular formula of acetic acid if the molar mass

of acetic acid is 60 , 06 g·mol−^1.

SOLUTION

Step 1:Find the mass

In 100 g of acetic acid, there is 39 , 9 g C, 6 , 7 g H and 53 , 4 g O

Step 2:Find the moles

346 Chemistry: Chemical change