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19/10/2021 10:27 am
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At 25°C, the dissociation constant of a base, BOH, is 1.0 x 10-12. The concentration of hydroxyl ions in 0.01 M aqueous solution of the base would be
(a) 1.0 x 10-5 mol L-1
(b) 1.0 x 10-6 mol L-1
(c) 2.0 x 10-6 mol L-1
(d) 1.0 x 10-7 mol L-1
1 Answer
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19/10/2021 10:35 am
Correct answer: (d) 1.0 x 10-7 mol L-1
Explanation:
Given Kb = 1.0 × 10-12
[BOH] = 0.01 M [OH]- = ?
BOH ⇌ B+ + OH-
t = 0 c 0 0
t = teq c(1 -α) cα cα
Kb = \(\frac{c^2\alpha^2}{c(1- \alpha)}\) = \(\frac{c \alpha^2}{(1-\alpha)}\)
⇒ 1.0 x 10-12 = \(\frac{0.01\alpha^2}{(1-\alpha)}\)
On calculation, we get, a = 1.0 × 10-5
Now, [OH]- = cα = 0.01 × 10-5
= 1 × 10-7 mol L-1