Question

What mass of ammonium chloride should you add to 2.15 l of a 0.135 moll−1 nh3 to obtain a buffer with a ph of 9.39? for ammonia, kb=1.76×10−5 .

Answer 1

To obtain a buffer with a pH of 9.39, you should add 20.95 g of ammonium chloride to 2.15 L of the given NH3 solution.

Step-by-step explanation:

First, we need to calculate the concentration of NH3 in the buffer solution. Since 1 mole of NH3 reacts with 1 mole of NH4Cl to form the buffer, the concentration of NH3 will be the same as the initial concentration of NH3, which is 0.135 M. Next, we can use the Henderson-Hasselbalch equation to calculate the ratio of NH4Cl to NH3 needed to achieve the desired pH:

pH = pKa + log([NH4Cl]/[NH3])

9.39 = 9.25 + log([NH4Cl]/0.135)

0.14 = log([NH4Cl]/0.135)

[NH4Cl]/0.135 = 10^(0.14)

[NH4Cl] = 0.135 × 10^(0.14)

[NH4Cl] = 0.135 × 1.414

[NH4Cl] = 0.191 M

Finally, to calculate the mass of NH4Cl needed, we can use the formula:

Mass = Concentration × Volume × Molar Mass

Mass = 0.191 × 2.15 × 53.50

Mass = 20.95 g