Calculate the concentration of buffer components present

Question

Calculate the concentration of buffer components present in 275.00 mL of a buffer solution that contains  0.240 M  NH₄Cl and 0.240 M  NH₃ immediately after the addition of 1.90 mL of 6.00 M  HNO₃.

A) Calculate the Concentration of NH₃

_{B) Calculate the Concentration of NH4}⁺

Answer 1

The original buffer solution contains a weak base, NH3 and its conjugate acid, NH₄⁺. Addition of the acid, HNO3, will react with the base, NH3 to produce NH₄⁺

Initial moles NH₃ = 275 ml x 1 L / 1000 ml x 0.240 mol / L = 0.066 mols

Initial moles NH₄⁺ = 275 ml x 1 L / 1000 ml x 0.240 mol / L = 0.066 mols

Initial moles HNO3 = 1.90 ml x 1 L / 1000 ml x 6.00 mol / L = 0.0114 mols

NH₃ + HNO₃ ==> NH₄⁺ + NO₃^-

0.066.......0.0114..........0.066...............Initial

-0.0114...-0.0114........+0.0114............Change

0.0515..........0...........0.0774.............Equilibrium

Final volume = 275 ml + 1.90 ml = 276.90 ml = 0.2769 L

Final [NH₃] = 0.0515 mol / 0.2769 L = 0.186 M

Final [NH₄⁺] = 0.0774 mol / 0.2769 L = 0.280 M