2SCS #13-17, p. 181

13) For the equation
3 PbO(s) + 2 NH3(g) --> 3 Pb(s) + N2(g) + 3 H2O(l)
a. how many moles NH3 are needed to react with 9 mol PbO?
b. how many moles N2 are produced by the reaction of 10 mol NH3?
c. how many moles Pb are produced from 5 mol PbO?

a. 6 moles NH3 are needed to react with 9 mol PbO.
b. 5 moles N2 are produced by the reaction of 10 mol NH3.
c. 5 moles Pb are produced from 5 mol PbO.

14) For the equation in Question 13,
a. how many moles (maximum) N2 can be produced from 34.0 g NH3?
b. what mass Pb can be produced from the complete reaction of 3.0 mol PbO?
c. what maximum mass N2 can be produced from 34.0 g NH2?
d. What mass PbO, which fully reacts, will produce 415 g Pb?

a. 1 mol N2 can be produced from 34.0 g NH3.
b. 621 g Pb can be produced from the complete reaction of 3.0 mol PbO.
c. 28 g N2 can be produced from 34.0 g NH2.
d. 415 g PbO, which fully reacts, will produce 415 g Pb.

15) In carbon dioxide, two-thirds of the atoms are oxygen atoms; however, the percent oxygen by mass is not 67%. Explain.

Although the percent of the oxygen atoms is 67%, since oxygen's molar mass is 32 and carbon's molar mass is 12 in this molecule, The percent oxygen by mass 32g/44g x 100%, or 73%.

16) Find the percent metal (by mass) in each of the following compounds:
a. Ag2S
b. Al2O3
c. CaCO3

a.
molar masses: Ag, 216g; S, 32g
216+32=248. 216g/248g x 100%=
87% silver by mass
b.
molar masses: Al, 54g; O, 48g
54+48=102. 54g/102g x 100%=
53% aluminum by mass
c.
molar masses: Ca, 40g; C, 12g; O, 48g
40+12+48=100. 40g/100g x 100%=
40% calcium by mass

17) A 50.0-g sample of ore contains 5.00 g lead(II) sulfate, PbSO4:
a. What is the percent lead (Pb) in PbSO4?
b. What is the percent PbSO4 in the ore sample?
c. What is the percent Pb in the total ore sample?
d. Use a diagram to represent the proportions of lead and lead(II) sulfate in the ore.

a.
molar masses: Pb, 207g; S, 32g; O, 64g
207+32+64=303. 207g/303g x 100%=
68% lead by mass
b.
5g/50g x 100%=
10% PbSO4 in the ore sample.
c.
68 x .10=
6.8% Pb in the total ore sample.
d.