Setting Up an ICE Table

Question

How many grams of NH₄Br must be dissolved in 1.00 L of water to produce a solution with pH = 5.16? The Kb of NH₃ is equal to 1.8 × 10⁻⁵.

How would I set up an ICE table and solve for the mass of NH4Br?

Answer 1

Not really sure you need an ICE table for this problem. I would do it as follows:

NH₄⁺ + H2O ==> NH₃ + H₃O⁺

[H3O⁺] = [NH₃] = 1x10^-5.16 = 6.9x10^-6 M

KaKb = 1x10^-14

Ka for NH₄⁺ = 1x10^-14 / 1.8x10^-5 = 5.6x10^-10

Ka = 5.6x10^-10 = [NH₃][H₃O⁺] / [NH₄⁺]

5.6x10^-10 = (6.9x10-6)² / [NH4+]

[NH4⁺] = (6.9x10^-6)² / 5.6x10^-10

[NH4⁺] = 8.5x10^-2 M

molar mass NH₄Br = 97.9 g/mole

8.5x10^-2 mol/L x 1 L x 97.9 g/mol = 8.32 g NH₄Br