Question

write equations needed to find the solubility of sr(oh)2. include the activity coefficients where appropriate. (b) then neglect activity coefficients and compute the solubility of sr(OH)2 in g/l

Answer 1

Solubility of Sr(OH)2 in water can be shown as follows:

Sr(OH)2(s) <-> Sr2+(aq)+ 2OH-(aq)

use Ksp for solubility expression

Ksp = A-Sr2+ * (A-OH-)^2

note that A- implies "activity"

Ksp = γ-Sr2++ *[ Sr2+] * γ-(OH-)^2 * [OH-]^2

now,

γi = activity coefficient for species “i”

b)

now, neglect acitivty coefficeints

i.e

γ-Sr2+ = 1

γ-(OH-) = 1

Ksp = γ-Sr2+ *[ Sr2+] * γ-(OH-)^2 * [OH-]^2

then

Ksp = 1*[ Sr2+] * 1^2 * [OH-]^2

Ksp = [Sr2+][OH-]^2

fin dsolubility in water

use your Ksp value, since Ksp value change with respect to reference books

Ksp Sr(OH)2 6.4 x 10-3

now,

Ksp = [Sr2+][OH-]^2

Assume

1 mol of Sr(OH) = 1 mol of Sr2+; 2 mol of OH-

S = Sr2+; 2S = OH-

substitute

Ksp = (S)(2S)^2

6.4*10^-3 = 4*S^3

S = ((6.4*10^-3)/(4))^(1/3)

S = 0.116960 mol per liter

now, we need grams per liter

1 mol fo Sr(OH)2 = 121.63 g/mol

121.63*0.116960 = 14.225 g of Sr(OH)2 per liter

now

Solubility = 14.225 g of Sr(OH)2 per liter