Question

Calculate the ionic strength that results when mixing 400 mL of 0.005 M Na₂SO₄ with 200 mL of 0.001 M Silver nitrate. Note: Silver sulfate is insoluble.

1. Write a charge balance for the system
2. Write a mass balance for the system
3. Find the concentration of silver if the pH is fixed at 7 given: Ksp = 1 x 10^-15, Ka₂ = 1 x 10^-2 for HSO₄^-

Answer 1

2AgNO3(aq)+Na2SO4(aq)→Ag2SO4(s)↓+2NaNO3(aq)

2Ag+ (aq) SO42-(aq) → Ag2SO4(s)↓ Net Ionic equation

Charge balance equation of any aqueous solution is:
n1[C1] + n2[C2] + ......... = m1[A1] + m2[A2] + .........
Charge Balance Equation
•C’s are the concentrations of all the (+)’ly charged ions.
•n is the magnitude of the (+) charge.
•A’s are the concentrations of all the (-)’ly charged ions.
•m is the magnitude of the (-) charge.

[Ag+] + [Na+] = 2{ [H3SO4-] + [H2SO42-] + [HSO43-] + [SO44-] } + [HNO3] + [NO3-]

Mass Balance Equation
The quantity of all species in a solution containing a particular atom (or group atoms) must equal the amount of that atom (or group atoms) delivered to the solution.

[H+] + [Ag+] + [Na+] = 2{ [H3SO4-] + [H2SO42-] + [HSO43-] + [SO44-] } + [HNO3] + [NO3-] + [OH-]

c. 2AgNO3(aq) → 2Ag+ + 2NO3-

Nitrate ion reacts with water to form HNO3

HNO3 → NO3- + H+

[Ag+] + [NO3-] = Ksp