Q1- A student measures the S 2- concentration in a saturated aqueous solution of

Question

Q1-

A student measures the S2- concentration in a saturated aqueous solution of calcium sulfide to be 2.94×10-3 M.  
Based on her data, the solubility product constant for calcium sulfide is  .

Q2- A student measures the molar solubility of silver phosphate in a water solution to be 4.76×10-6 M.  
Based on her data, the solubility product constant for this compound is  .

Q3- A student measures the molar solubility of lead hydroxide in a water solution to be 4.03×10-6 M.  
Based on her data, the solubility product constant for this compound is  .

Explanation / Answer

1)

At equilibrium:

CaS <----> Ca2+ + S2-

   s s

Ksp = [Ca2+][S2-]

Ksp = (s)*(s)

Ksp = 1(s)^2

Ksp = 1(2.94*10^-3)^2

Ksp = 8.644*10^-6

Answer: 8.64*10^-6

2)

At equilibrium:

Ag3PO4 <----> 3 Ag+ + PO43-

   3s s

Ksp = [Ag+]^3[PO43-]

Ksp = (3s)^3*(s)

Ksp = 27(s)^4

Ksp = 27(4.76*10^-6)^4

Ksp = 1.386*10^-20

Answer: 1.39*10^-20

3)

At equilibrium:

Pb(OH)2 <----> Pb2+ + 2 OH-

   s 2s

Ksp = [Pb2+][OH-]^2

Ksp = (s)*(2s)^2

Ksp = 4(s)^3

Ksp = 4(4.03*10^-6)^3

Ksp = 2.618*10^-16

Answer: 2.62*10^-16

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