1 (112)

Prévia do material em texto

CHAPTER 4: REACTIONS IN AQUEOUS SOLUTIONS 
 
111
 
 4) 4
4
159.62 g CuSO
1.032 mol
1 mol CuSO
× = 4165 g CuSO 
 5) 63.55 g Cu1.032 mol
1 mol Cu
× = 65.6 g Cu 
 
 (c) All of the reaction steps are clean and almost quantitative; therefore, the recovery yield should be high. 
 
4.152 The first titration oxidizes Fe2+ to Fe3+. This titration gives the amount of Fe2+ in solution. Zn metal is 
added to reduce all Fe3+ back to Fe2+. The second titration oxidizes all the Fe2+ back to Fe3+. We can find 
the amount of Fe3+ in the original solution by difference. 
 
 Titration #1: The mole ratio between Fe2+ and MnO4
− is 5:1. 
 
 
2
3 24
4
0.0200 mol MnO 5 mol Fe23.0 mL soln 2.30 10 mol Fe
1000 mL soln 1 mol MnO
− +
− +
−
× × = × 
 
 
3 2
3
mol solute 2.30 10 mol Fe
L of soln 25.0 10 L soln
− +
−
×
= = =
×
2+[Fe ] 0.0920 M 
 
 Titration #2: The mole ratio between Fe2+ and MnO4
− is 5:1. 
 
 
2
3 24
4
0.0200 mol MnO 5 mol Fe40.0 mL soln 4.00 10 mol Fe
1000 mL soln 1 mol MnO
− +
− +
−
× × = × 
 
 In this second titration, there are more moles of Fe2+ in solution. This is due to Fe3+ in the original solution 
being reduced by Zn to Fe2+. The number of moles of Fe3+ in solution is: 
 
 (4.00 × 10−3 mol) − (2.30 × 10−3 mol) = 1.70 × 10−3 mol Fe3+ 
 
 
3 3
3
mol solute 1.70 10 mol Fe
L of soln 25.0 10 L soln
− +
−
×
= = =
×
3+[Fe ] 0.0680 M
 
 
4.153 Place the following metals in the correct positions on the periodic table framework provided in the problem. 
 
 (a) Li, Na (Group 1A) (b) Mg (Group 2A), Fe (Group 8B) (c) Zn, Cd (Group 2B) 
 
 Two metals that do not react with water or acid are Ag and Au (Group 1B). 
 
4.154 (a) The precipitation reaction is: Mg2+(aq) + 2OH−(aq) ⎯⎯→ Mg(OH)2(s) 
 
 The acid-base reaction is: Mg(OH)2(s) + 2HCl(aq) ⎯⎯→ MgCl2(aq) + 2H2O(l) 
 
 The redox reactions are: Mg2+ + 2e− ⎯⎯→ Mg 
 2Cl− ⎯⎯→ Cl2 + 2e− 
 MgCl2 ⎯⎯→ Mg + Cl2 
 
 (b) NaOH is much more expensive than CaO. 
 
 (c) Dolomite has the advantage of being an additional source of magnesium that can also be recovered.