1. Chapter 10 NOTES
PRACTICE PROBLEMS

2. Try it on your own!
A compound is formed when 9.03 g Mg combines completely with 3.48 g N. What is the percent composition of this compound?
Known
Mass of Mg = 9.03g
Mass of N = 3.48 g
Total mass of cmpd. = g (9.03g g)
Unknown
% Mg = ?
% N = ?

3. Solve % Mg = 9.03 g x 100% = 72% 12.51 g % N = 3.48 g x 100% = 28%

4. Try it on your own!
When a 14.2-g sample of mercury(II) oxide is decomposed into its elements by heating, 13.2 g Hg is obtained. What is the percent composition of the compound?
Known
Mass of cmpd = 14.2g
Mass of Hg = 13.2 g
Mass of O = 1.0 g (14.2g – 13.2g)
Unknown
% Hg = ?
% O = ?

5. Solve
% Hg = 13.2g x 100% = 93% 14.2g % O = 1.0g x 100% = 7%

6. Try it on your own!
Calculate the percent composition of ethane (C2H6).
Know: mass of C in 1 mol ethane= 2X12=24g
Mass of H in 1 mol ethane=1X6=6g
Unknown: Percent C?
Percent H?
Molar mass= 24g+6g= 30g

7. Solve
%C= 24g X 100 = 80%
30g
%H= 6g X 100= 20%
% equals 100!

8. Try it on your own Calculate the percent nitrogen in NH₄NO₃
Know: mass of N in 1 mol NH₄NO₃= 14X2=28g
Know: molar mass NH₄NO₃= (14X2)+(4X1)+(3X16)= 28g
Unknown: percent N?

9. Solve % N = 28g X 100 = 35% 80g This is correct because:
%H= 4g X100 = 5%
%O = 48g X 100= 60%