Everything Science Grade 10

CHAPTER 19. QUANTITATIVE ASPECTS OF CHEMICAL CHANGE 19.2

Use the ratios of molar numbers calculated above to find the empirical

formula.

units in empirical formula=smallest number of molesmoles of this element

In this case, the smallest number of moles is 2 , 175. Therefore:

Carbon

4 , 35

2 , 175 = 2

Hydrogen

12 , 871

2 , 175 = 6

Oxygen

2 , 175

2 , 175 = 1

Therefore the empirical formula of this substance is: C 2 H 6 O.

Example 9: Determining the formula of a compound

QUESTION

207 g of lead combines with oxygen to form 239 g of a lead oxide. Use this

information to work out the formula of the lead oxide (Relative atomic masses:

Pb= 207, 2 u and O= 16, 0 u).

SOLUTION

Step 1:Find the mass of oxygen

239 g− 207 g= 32g

Chemistry: Chemical change 345