Question

how much of 10% sodium carbonate would be needed to bring 1.5mL of Na2SO4 (sulfuric acid) [18M] to a pH of ~8?

Answer 1

Note: I think there is a mistake in this question because these an uncommon expression "1.5mL of Na₂SO₄ (sulfuric acid) [18M]" but, you will need:

pOH = 14 - 8

pOH = 6

OH^-_final = 1x10^-6

pOH of Na₂SO₄ solution = 7.0

OH^-_initial = 1x10^-7 M

1x10^-6 - 1x10^-7 = 9x10^-7

CO₃^2- + H₂O HCO₃^- + OH^-

Kb = [HCO₃^-][OH^-]                  [CO₃^2-] = [HCO₃^-][OH^-]              [CO₃^2-] = [OH^-]²

[CO₃^2-] Kb                                       Kb

[CO₃^2-] = 9x10^-7 / 2.3x10^-8              [CO₃^2-] = 39.1304

I need to know final volume, but final concentration of carbonate should be 39.1304M