Question

1- What is the pH of a solution made by dissolving 3.26 grams of calcium fluoride in enough water to make 3.0×102 mL of solution? The Ka for HF is 6.8x10–4.

2- The Kb of dimethylamine [(CH3)2NH] is 5.90x10–4 at 25°C. Calculate the pH of a 0.0930 M solution of dimethylamine.

Answer 1

1

Initial concentration (M)	0.2786	0	0
Change in concentration (M)	-x	+x	+x
Equilibrium concentration (M)	0.2786-x	x	x

The equilibrium constant

..... (1)

But

......(2)

But (1)=(2)

Since Kb is very small, we approxiamte 0.2786-x to 0.2786