Question

What mass of ammonium chloride should be added to 2.55 l of a 0.160 m NH₃ to obtain a buffer with a ph of 9.65? ( kb for NH₃ is 1.8×10⁻⁵ .)

Answer 1

To find the necessary mass of NH4Cl to create a buffer with a specific pH, use the Henderson-Hasselbalch equation to determine the concentration of NH4+ required. Then, convert this concentration to moles and finally to grams using the molar mass of NH4Cl.

Step-by-step explanation:

To calculate the mass of ammonium chloride (NH4Cl) needed to create a buffer solution with a pH of 9.65 in a 2.55 L of 0.160 M NH3 solution, we will use the Henderson-Hasselbalch equation. Given that the pH is 9.65 and the pKa of ammonium (NH4+) is approximately 9.25, we start by calculating the ratio of the concentrations of NH4+ to NH3. The Henderson-Hasselbalch equation is:

pH = pKa + log([NH4+]/[NH3])

Rearranging the equation for the concentration of [NH4+], we get:

[NH4+] = [NH3] × 10^(pH-pKa)

This is the concentration of NH4+ needed to achieve the desired pH. The mass of NH4Cl needed is then found by converting this concentration to moles (considering the volume of the solution), and then to grams using the molar mass of NH4Cl.