Question

Merrell What is the pH of a saturated solution of Ni(OH),? Kg (Ni(OH)2) = 2.8 x 10-16 pH = What is the solubility in grams of Ni(OH),/100. mL of solution? Solubility = g/100 mL Submit Answer Try Another Version

Answer 1

1)

At equilibrium:

Ni(OH)2 <----> Ni2+ + 2 OH-

   s 2s

Ksp = [Ni2+][OH-]^2

2.8*10^-16=(s)*(2s)^2

2.8*10^-16= 4(s)^3

s = 4.121*10^-6 M

So,

[OH-] = 2s

= 2*4.121*10^-6 M

= 8.242*10^-6 M

use:

pOH = -log [OH-]

= -log (8.242*10^-6)

= 5.08

use:

PH = 14 - pOH

= 14 - 5.08

= 8.92

Answer: 8.92

2)

Molar mass of Ni(OH)2,

MM = 1*MM(Ni) + 2*MM(O) + 2*MM(H)

= 1*58.69 + 2*16.0 + 2*1.008

= 92.706 g/mol

Molar mass of Ni(OH)2= 92.706 g/mol

s = 4.121*10^-6 mol/L

To covert it to g/L, multiply it by molar mass

s = 4.121*10^-6 mol/L * 92.706 g/mol

s = 3.821*10^-4 g/L

s = 3.821*10^-4 g/1000 mL

s = 3.821*10^-5 g/100 mL

Answer: 3.82*10^-5 g/100mL