Acid-Base Equilibria And Buffer Solutions Worksheet With Answers Page 2
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1
2
3
4
5Chem 1B
Chapter 15 Exercises
+
4.
(a) Calculate [H
O
] and the pH of a solution that contains 0.10 M NH
and 0.10 M NH
Cl.
3
3
4
–
–
+
10
+
10
(K
(NH
) = 5.6 x 10
)
(Answer: (a) [H
O
] = 5.6 x 10
M, pH = 9.25)
a
4
3
+
(b) Calculate [H
O
] and the pH a solution that contains 0.20 M NH
and 0.10 M NH
Cl.
3
3
4
–
+
10
(Answers: [H
O
] = 2.8 x 10
M, pH = 9.55)
3
5.
Indicate whether each of the following solution combinations will make a buffer solution. Explain.
(a) 50.0 mL of 0.20 M HCl + 50.0 mL of 0.20 M NaCl;
(b) 50.0 mL of 0.20 M HNO
+ 50.0 mL of 0.20 M NaNO
;
2
2
(c) 50.0 mL of 0.20 M CH
CO
H + 50.0 mL of 0.20 M NaCH
CO
;
3
2
3
2
(d) 50.0 mL of 0.20 M CH
CO
H + 50.0 mL of 0.20 M NaOH;
3
2
(e) 50.0 mL of 0.20 M CH
CO
H + 50.0 mL of 0.10 M NaOH;
3
2
(f) 50.0 mL of 0.20 M CH
CO
H + 50.0 mL of deionized water;
3
2
(g) 50.0 mL of 0.20 M NH
+ 50.0 mL of 0.20 M NH
NO
;
3
4
3
(h) 50.0 mL of 0.20 M NH
+ 50.0 mL of 0.20 M HNO
;
3
3
(i) 50.0 mL of 0.20 M NH
+ 50.0 mL of 0.10 M HNO
;
3
3
(j) 50.0 mL of 0.20 M NH
+ 50.0 mL of deionized water;
3
(k) 50.0 mL of 0.20 M NH
NO
+ 50.0 mL of 0.20 M NaOH;
4
3
(l) 50.0 mL of 0.20 M NH
NO
+ 50.0 mL of 0.10 M NaOH;
4
3
6.
A phosphate buffer solution is prepared by dissolving 25.0 g of potassium hydrogen phosphate
(K
HPO
; FM = 174.18) and 12.0 g of potassium dihydrogen phosphate (KH
PO
; FM = 136.09) in
2
4
2
4
250. mL of the buffer solution.
-
–
2
(a) Calculate the molar concentrations of HPO
and H
PO
, respectively, and the pH of the buffer
4
2
solution using the following equilibrium:
–
O ⇌ H
–
–
+
2
8
H
PO
+ H
O
+ HPO
;
(K
= 6.2 x 10
)
(aq)
(aq)
(aq)
2
4
2
3
4
a
(b) Write an equation for the buffering reaction: (i) when a strong acid is added; (ii) when a strong base
is added to the phosphate buffer solution.
(c) Calculate the final pH of the solution: (i) when 2.0 mL of 6.0 M HCl
is added to the buffer; (ii)
(aq)
when 2.0 mL of 6.0 M NaOH
is added to the buffer. (In each case, assume the final volume of the
(aq)
solution is 250. mL)
–
–
2
(Answer: (a) [HPO
] = 0.574 M; [H
PO
] = 0.353 M, and pH = 7.42;
4
2
(c) (i) pH = 7.33; (ii) pH = 7.52)
2
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