Chemistry 121 – Summer 2008 – Worksheet #7
1. Like many metals, aluminum reacts with a halogen to give a metal halide according to
the following equation:
+ 3 Br2 (l) 
2 Al (s)
Al2Br6 (s)
(a) What mass of Br2, in grams, is required for complete reaction with 2.56 g of
Al?
Al = known, atomic mass = 26.98 g/ mol
Br2 = target, atomic mcass = 159.81 g/ mol
Stoich ratio = (3 mol Br2 / 2 mol Al)
1. mol Al = 2.56 g × (1 mol Al / 26.98 g Al) = 0.0949 mol Al
2. mol Br2 = 0.0949 mol Al × (3 mol Br2 / 2 mol Al) = 0.412 mol Br2
3. g Br2 = 0.412 mol Br2 × (159.81 g Br2 / 1 mol Br2) = 22.7 g Br2
(b) What mass of white, solid Al2Br6 is expected?
By Law of Conservation of Mass
g Al2Br6 = 2.56 g Al + 22.7 g Br2 = 25.3 g Al2Br6
2. Sulfur dioxide, a pollutant produced by burning coal and oil in power plants, can be
removed by reaction with calcium carbonate.
2 SO2 (g)
+ 2 CaCO3 (s)
+
O2 (g)

2 CaSO4 (s)
+ 2 CO2 (g)
(a) What mass of CaCO3 is required to completely remove 155 g of SO2?
SO2 = known, atomic mass = 64.06 g/ mol
CaCO3 = target, atomic mcass = 100.09 g/ mol
Stoich ratio = (2 mol CaCO3/ 2 mol SO2)
1. mol SO2 = 155 g × (1 mol SO2 / 64.06 g SO2) = 2.42 mol SO2
2. mol CaCO3 = 2.42 mol SO2 × (2 mol CaCO3 / 2 mol SO2)
= 2.42 mol CaCO3
3. g CaCO3 = 2.42 mol CaCO3 × (100.09 g CaCO3 / 1 mol CaCO3)
= 242 g CaCO3
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(b) What mass of CaSO4 is formed when 155 g of SO2 is consumed completely?
Because CO2 is also a product, cannot use Law of Conservation of Mass,
have to calculate.
SO2 = known, atomic mass = 64.06 g/ mol
CaSO4 = target, atomic mcass = 136.14 g/ mol
Stoich ratio = (2 mol CaSO4 / 2 mol SO2)
Already know mol mol SO2 = 2.42 mol SO2
2. mol CaSO4 = 2.42 mol SO2 × (2 mol CaSO4 / 2 mol SO2)
= 2.42 mol CaSO4
3. g CaSO4 = 0.412 mol CaSO4 × (136.14 g CaSO4 / 1 mol CaSO4)
= 329 g CaSO4
3. Which of the following mixtures of compounds in water will result in a precipitate,
and what is it?
(a) Sodium chloride and magnesium nitrate
Possible products = NaNO3 and MgCl2 – both soluble, no precipitate
(b) Silver nitrate and ammonium sulfide
Possible products = AgS and NH4NO3 – AgS is insoluble and is a precipitate
(c) Iron (III) bromide and barium hydroxide
Possible products = Fe(OH)3 and BaBr2
– Fe(OH)3 is insoluble and is a precipitate
Note that BaBr2 is a bromide, but not of Ag+, Pb2+ or Hg22+, so it is soluble
4. Write the net ionic equation when zinc nitrate and ammonium phosphate are
dissolved separately in water and then mixed.
Full equation:
3Zn(NO3)2 (aq) + 2(NH4)3PO4 (aq)  2Zn3(PO4)2 (s) + 6NH4NO3 (aq)
NH4+ and NO3- are spectator ions.
Net ionic equation:
3Zn2+(aq) + 2PO43- (aq)  Zn3(PO4)2 (s)
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5. What is the balanced equation for the reaction of solid magnesium carbonate and an
aqueous solution of nitric acid (HNO3)?
Gas-producing reaction (CO2).
MgCO3(s) + 2HNO3(aq)  CO2(g) + Mg(NO3)2 (aq) + H2O(l)
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