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 gā 207 g= 32g
Chemistry: Chemical change 345