Page 166 - Theory and Problems of BEGINNING CHEMISTRY

CHAP. 10] STOICHIOMETRY 155

2 mol Na
Ans. (a) 0.400 mol Cl 2 = 0.800 mol Na required
1 mol Cl 2
There is 0.40 mol more Na present than is required.
6 mol H 2 O

(b) 0.25 mol P 4 O 10 = 1.5 mol H 2 O required
1 mol P 4 O 10
Neither reagent is in excess; there is just enough H 2 O to react with all the P 4 O 10 .

1 mol HNO 3
(c) 0.85 mol NaOH = 0.85 mol HNO 3 required
1 mol NaOH
There is not enough NaOH present; HNO 3 is in excess.
There is 0.05 mol HNO 3 in excess.
2 mol HCl

(d) 1.0 mol Ca(HCO 3 ) 2 = 2.0 mol HCl required
1 mol Ca(HCO 3 ) 2
There is 0.5 mol HCl in excess.
3 mol NaOH

(e) 0.70 mol H 3 PO 4 = 2.1 mol NaOH required
1 mol H 3 PO 4
There is 2.2 − 2.1 = 0.1 mol NaOH in excess.
10.35. For the following reaction,

2 NaOH + H 2 SO 4 −→ Na 2 SO 4 + 2H 2 O

(a) How many moles of NaOH would react with 0.250 mol H 2 SO 4 ? How many moles of Na 2 SO 4 would
be produced?
(b) If 0.250 mol of H 2 SO 4 and 0.750 mol NaOH were mixed, how much NaOH would react?
(c) If24.5gH 2 SO 4 and 30.0 g NaOH were mixed, how many grams of Na 2 SO 4 would be produced?

Ans. (a) 2 mol NaOH
0.250 mol H 2 SO 4 = 0.500 mol NaOH
1 mol H 2 SO 4

1 mol Na 2 SO 4
0.250 mol H 2 SO 4 = 0.250 mol Na 2 SO 4
1 mol H 2 SO 4
(b) 0.500 mol NaOH, as calculated in part (a).
(c) This is really the same problem as part (b), except that it is stated in grams, because 24.5 g H 2 SO 4 is
0.250 mol and 30.0 g NaOH is 0.750 mol NaOH.

142gNa 2 SO 4
To finish: 0.250 mol Na 2 SO 4 = 35.5gNa 2 SO 4
1 mol Na 2 SO 4
10.36. For the reaction

3 HCl + Na 3 PO 4 −→ H 3 PO 4 + 3 NaCl

a chemist added 2.55 mol of HCl and a certain quantity of Na 3 PO 4 to a reaction vessel, which produced
0.750 mol H 3 PO 4 . Which one of the reactants was in excess?

1 mol H 3 PO 4
Ans. 2.55 mol HCl = 0.850 mol H 3 PO 4
3 mol HCl
would be produced by reaction of all the HCl. Since the actual quantity of H 3 PO 4 produced is 0.750 mol,
not all the HCl was used up and the Na 3 PO 4 must be the limiting quantity. The HCl was in excess.
10.37. (a) How many moles of Cl 2 will react with 1.22 mol Na to produce NaCl? (b) If 0.880 mol Cl 2 is treated
with 1.22 mol Na, how much Cl 2 will react? (c) What is the limiting quantity in this problem?