Everything Science Grade 10

19.2 CHAPTER 19. QUANTITATIVE ASPECTS OF CHEMICAL CHANGE

(You should check at the end that these percentages add up to100%!)

In other words, in one molecule of sulphuric acid, hydrogen makes

up 2 ,06%of the mass of the compound, sulphur makes up 32 ,71%and

oxygen makes up 65 ,23%.

Example 8: Determining the empirical formula of a com-

pound

QUESTION

A compound contains 52 ,2%carbon (C), 13 ,0%hydrogen (H) and 34 ,8%oxygen

(O). Determine its empirical formula.

SOLUTION

Step 1:Give the masses

Carbon= 52, 2 g, hydrogen= 13, 0 g and oxygen= 34, 8 g

Step 2:Calculate the number of moles

n=Mm

Therefore:

n(Carbon) =^52 ,^2 g

12 , 0 g·mol−^1

= 4, 35 mol

n(Hydrogen) =^13 ,^0 g

1 , 01 g·mol−^1

= 12, 871 mol

n(Oxygen) =^34 ,^8 g

16 , 0 g·mol−^1

= 2, 175 mol

Step 3:Find the smallest number of moles

344 Chemistry: Chemical change