Page 161 - Theory and Problems of BEGINNING CHEMISTRY

150 STOICHIOMETRY [CHAP. 10

10.6. Balance the following equation. Calculate the number of moles of CO 2 that can be prepared by the
reaction of 2.50 mol of Mg(HCO 3 ) 2 .
Mg(HCO 3 ) 2 + HCl −→ MgCl + CO 2 + H 2 O
2
Ans. Mg(HCO 3 ) 2 + 2 HCl −→ MgCl + 2CO 2 + 2H 2 O
2

2 mol CO 2
2.50 mol Mg(HCO ) 2 = 5.00 mol CO 2
3
1 mol Mg(HCO ) 2
3
10.7. (a) How many moles of CaCl 2 can be prepared by the reaction of 2.50 mol HCl with excess Ca(OH) 2 ?
(b) How many moles of NaCl can be prepared by the reaction of 2.50 mol HCl with excess NaOH?
Ans. (a)Ca(OH) 2 + 2 HCl −→ CaCl 2 + 2H 2 O

1 mol CaCl 2
2.50 mol HCl = 1.25 mol CaCl 2
2 mol HCl
(b) NaOH + HCl −→ NaCl + H 2 O
1 mol NaCl

2.50 mol HCl = 2.50 mol NaCl
1 mol HCl
10.8. How many moles of H 2 O are prepared along with 0.750 mol Na 3 PO 4 in a reaction of NaOH and H 3 PO 4 ?
Ans. H 3 PO 4 + 3 NaOH −→ Na 3 PO 4 + 3H 2 O
3 mol H 2 O

0.750 mol Na 3 PO 4 = 2.25 mol H 2 O
1 mol Na 3 PO 4
10.9. Consider the following equation:
KMnO 4 + 5 FeCl 2 + 8 HCl −→ MnCl 2 + 5 FeCl 3 + 4H 2 O + KCl

How many moles of FeCl 3 will be produced by the reaction of 0.968 mol of HCl?
Ans. No matter how complicated the equation, the reacting ratio is still given by the coefficients. The coefficients
of interest are 8 for HCl and 5 for FeCl 3 .

5 mol FeCl 3
0.968 mol HCl = 0.605 mol FeCl 3
8 mol HCl
Note: The hard part of this problem is balancing the equation, which will be presented in Chap. 14. Since the
balanced equation was given in the statement of the problem, the problem is as easy to solve as the previous
ones.

CALCULATIONS INVOLVING OTHER QUANTITIES
10.10. Figure 10-2 is a combination of which two earlier figures?
Ans. Figures 10-1 and 7-2.

10.11. Which earlier sections must be understood before mass-to-mass conversions can be studied profitably?
Ans. Section 2.2, factor-label method; Sec. 7.3, calculation of formula masses; Sec. 7.4, changing moles to grams
and vice versa; Sec. 7.4, Avogadro’s number; and/or Sec. 8.2, balancing chemical equations.
10.12. In a stoichiometry problem, (a) if the mass of a reactant is given, what conversions (if any) should be
made? (b) If a number of molecules is given, what conversions (if any) should be made? (c) If a number
of moles is given, what conversions (if any) should be made?
Ans. (a) The mass should be converted to moles. (b) The number of molecules should be converted to moles.
(c) No conversion need be done; the quantity is given in moles.
10.13. Phosphoric acid reacts with sodium hydroxide to produce sodium phosphate and water. (a) Write a
balanced chemical equation for the reaction. (b) Determine the number of moles of phosphoric acid in
50.0 g of the acid. (c) How many moles of sodium phosphate will be produced by the reaction of this