Answer to Question #341747 in General Chemistry for Hsjskowjhz

Question

Calculate the ratio of ammonium chloride to ammonia that is required to make a buffer solution with a pH of 9.00. The Ka for ammonium ion is 5.6 x 10-10.

Answer 1

Solution:

The pH of the buffer solution can be calculated from the Henderson-Hasselbalch equation:

where the base is ammonia (NH₃) and the acid is ammonium chloride (NH₄Cl).

You can rearrange this equation to solve for the ratio of ammonia to ammonium chloride:

[NH₃] / [NH₄Cl] = 10^{(pH − pKa)}

pK_a = −log(K_a) = −log(5.6×10⁻¹⁰) = 9.25

pH = 9.00

Therefore,

[NH₃] / [NH₄Cl] = 10^{(9.00 − 9.25)} = 10^−0.25 = 0.5623

[NH₃] / [NH₄Cl] = 0.5623

Calculate the ratio of ammonium chloride to ammonia:

[NH₄Cl] / [NH₃] = (0.5623)⁻¹ = 1.78

[NH₄Cl] / [NH₃] = 1.78

Answer: The ratio of ammonium chloride to ammonia is 1.78