1. Many important metals occur as sulfide, arsenide, and antimonide minerals, especially in the Sudbury mineral complex. The first step in processing these ores involves "roasting" the ore in air to produce the metal or metal oxide, along with nonmetal oxides that can be serious pollutants if not trapped.
Suppose that you roast 1.00 kg of the mineral shandite, Ni3Pb2S2. The balanced equation for the reaction is:
2Ni3Pb2S2 + 9O2 → 6NiO + 4 PbO + 4SO2
(a) How many kg of NiO can be produced?
(b) How many kg of the pollutant PbO can be produced?
(c) How many liters of air at 25°C are required for roasting? Assume that air contains 23% O2 by mass, and that the density of air at 25°C is 1.2 g/L.
Molar masses: Ni3Pb2S2 654.6 g/mol NiO 74.69 g/mol PbO 223.20 g/mol
2. A mixture of Na2SO4 and its hydrate Na2SO4•10H2O has a mass of 1.8092 g. After heating to drive off all the water, the mass is only 1.6526 g. What is the weight percentage of Na2SO4•10H2O in the original mixture?
Report your answer to 4 significant figures.
Molar masses: Na2SO4 142.04 g/mol; Na2SO4•10H2O 322.19 g/mol.
3. MnCl2 reacts with AgNO3 in aqueous solutions to produce a precipitate of AgCl that can be filtered and weighed. The balanced equation for the reaction is:
MnCl2 (aq) + 2 AgNO3 (aq) → 2 AgCl (s) + Mn(NO3)2 (aq)
Suppose you have a mixture that contains MnCl2, plus other compounds that do not react with AgNO3. If 0.4033 g of the mixture yields 0.6589 g of AgCl, what is the percentage of MnCl2 in the mixture?
Molar masses: MnCl2 125.84 g/mol AgCl 143.32 g/mol
4. Potassium perchlorate is used in the production of fireworks and explosives. It is made in a two-step reaction. First, potassium hypochlorite disproportionates to potassium chloride and potassium chlorate. Then the potassium chlorate disproportionates again to form potassium perchlorate and potassium chloride. The equations are:
3 KClO (aq) → 2 KCl (aq) + KClO3 (aq)
4 KClO3 (aq) → 3 KClO4 (s) + KCl (aq)
What mass of KClO4 (in kg) can be obtained from 3.40 kg of KClO when these reactions are carried out? Molar masses (g/mol): KClO 90.55 KClO4 138.55
5. An organic compound containing only C, H, and possibly O was subjected to combustion analysis. A sample weighing 0.5567 g yielded 0.941 g CO2 and 0.385 g H2O. What is the empirical formula of the compound?
6. For the complete redox reaction given here, (a) break down each reaction into its half reactions; (b) identify the oxidizing agent; and (c) identify the reducing agent.
O2 + 2Zn → 2ZnO
7. Give the oxidation number of nitrogen in each of the following compounds or ions:
(a) Mg(NO2)2
(b) Li3N
(c) N2H2
(d) N2O3
(e) NO3-
8.
Consider the following net ionic equation for a redox reaction:
5 H2O2 + 2 MnO4- + 6 H+ → 5O2 + 2 Mn2+ + 8H2O
(a) Which reactant gets oxidized?
(b) Which reactant gets reduced?
(c) Which reactant is the oxidizing agent? (d) Which reactant is the reducing agent?