Question

The mass of chromium(III) hydroxide that is dissolved in 150 mL of a saturated solution is _______ grams.

Answer 1

The salt dissolves as:

Cr(OH)3 <----> Cr3+ + 3 OH-

   s 3s

Ksp = [Cr3+][OH-]^3

6.7*10^-31=(s)*(3s)^3

6.7*10^-31= 27(s)^4

s = 1.255*10^-8 M

Molar mass of Cr(OH)3 = 1*MM(Cr) + 3*MM(O) + 3*MM(H)

= 1*52.0 + 3*16.0 + 3*1.008

= 103.024 g/mol

Molar mass of Cr(OH)3= 103.024 g/mol

s = 1.255*10^-8 mol/L

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

s = 1.255*10^-8 mol/L * 103.024 g/mol

s = 1.293*10^-6 g/L

here volume = 150 mL =    0.150 L

So,

mass = s*volume

= 1.293*10^-6 g/L * 0.150 L

= 1.94*10^-7 g

Answer: 1.94*10^-7 g