Question

Calculate the concentration of buffer components present in 287.00 mL of a buffer solution that contains 0.310 M NH4Cl and 0.310 M NH3 immediately after the addition of 1.50 mL of 6.00 M HNO3.

Answer 1

Answer:

NH₄⁺: 0.340M

NH₃: 0.277M

Explanation:

A buffer is the mixture of a strong acid with its conjugate base.

For the buffer of NH₃ / NH₄⁺, moles of each one are:

NH₄⁺: 0.287L × (0.310mol / L) = 0.0890 moles

NH₃: 0.287L × (0.310mol / L) = 0.0890 moles

The reaction of HNO₃ with NH₃ is:

HNO₃ + NH₃ →  NH₄⁺ + NO₃⁻

Moles of 1.50mL of 6.00M HNO₃ are:

1.50x10⁻³L × (6.00mol / L) = 9x10⁻³ moles of HNO₃. These moles are moles produced of NO₃⁻ and consumed of NH₃. Thus moles after reaction are:

NH₄⁺: 0.0890 moles + 0.0090 moles = 0.0980moles

NH₃: 0.0890 moles + 0.0090 moles = 0.0800moles

As total volume is 287.00mL + 1.50mL = 288.50mL (0.28850L), concentrations are:

NH₄⁺: 0.0980moles / 0.28850L = 0.340M

NH₃: 0.0800moles / 0.28850L = 0.277M