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LSM 16.1D
Solutions for Kw, pH, and pOH Calculations,
Extra Exercises
1. Calculate the [OH(aq)] in limes which have a [H3O+(aq)] of 1.3 × 10-2 mol/L.
Kw
1.0 × 10-14 (mol/L)2
[OH - (aq)] =
=
= 7.7 × 10-13 mol/L
+
-2
[H 3 O (aq)]
1.3 × 10 mol/L
2. Calculate the [H3O+(aq)] in lemons which have a [OH-(aq)] of 2.0 × 10-12 mol/L.
Kw
1.0 × 10-14 (mol/L)2
[H 3O + (aq)] =
=
= 5.0 × 10-3 mol/L
[OH - (aq)]
2.0 × 10-12 mol/L
3. A sodium hydroxide solution is prepared by dissolving 2.50 g to make 2.00 L of solution.
Calculate the hydroxide and hydronium ion concentrations.
1 mol
nNaOH = 2.50 g ×
= 6.25 × 10-2 mol
40.00 g
6.25 × 10-2 mol
[NaOH(aq)] =
= 3.13 × 10-2 mol/L
2.00 L
[OH - (aq)] = [NaOH(aq)] = 3.13 × 10-2 mol/L
[H 3O + (aq)] =
Kw
1.0 × 10-14 (mol/L)2
=
= 3.2 × 10-13 mol/L
[OH - (aq)]
3.13 × 10-2 mol/L
4. A 0.728 g sample of hydrogen chloride gas is dissolved in 200 mL of solution. Calculate the
hydronium and hydroxide ion concentrations.
1 mol
nHCl = 0.728 g ×
= 2.00 × 10-2 mol
36.46 g
2.00 × 10-2 mol/L
[HCl(aq)] =
= 9.98 × 10-2 mol/L
0.200 L
[H 3 O + (aq)] = [HCl(aq)] = 9.98 × 10-2 mol/L
[OH - (aq)] =
Kw
1.0 × 10-14 (mol/L)2
=
= 1.0 × 10-13 mol/L
[H 3 O + (aq)]
9.98 × 10-2 mol/L
5. Vinegar has a hydronium ion concentration of 1.5 × 10-3 mol/L. Calculate the pH.
pH = - log[H 3 O + (aq)] = - log(1.5 × 10-3 ) = 2.82
6. An ammonia solution has a pOH of 2.92. What is the concentration of hydroxide ions in the
solution?
[OH - (aq)] = 10-pOH = 10-2.92 mol/L = 1.2 ×10-3 mol/L
Copyright © 2007 Thomson Nelson
Unit 8 Lab and Study Masters
521
LSM 16.1D (cont’d)
7. Calculate the pOH and pH of a solution made by dissolving 7.50 g of strontium hydroxide to
make 500 mL of solution.
1 mol
nSr(OH)2 = 7.50 g ×
= 0.0617 mol
121.64 g
0.0617 mol
[Sr(OH)2 (aq)] =
= 0.123 mol/L
0.500 L
[OH - (aq)] = 2 [Sr(OH)2 (aq)] = 2 × 0.123 mol/L = 0.247 mol/L
pOH = - log[OH - (aq) ] = - log(0.247) = 0.608
pH = 14.000 - 0.608 = 13.392
8. Complete the following table.
Table 1 pH of Common Substances
Substance
milk
pure water
blood
cleaner
522
[H3O+(aq)]
(mol/L)
3.1 × 10-7
1 × 10-7
4.0 × 10-8
1.6 × 10-11
Unit 8 Lab and Study Masters
pH
6.51
7.0
7.40
10.80
[OH-(aq)]
(mol/L)
3.2 × 10-4
1 × 10-7
2.5 × 10-7
6.3 × 10-4
pOH
7.49
7.0
6.60
3.20
Acidic,
basic, or
neutral
acidic
neutral
basic
basic
Copyright © 2007 Thomson Nelson