Question

Para-aminobenzoic acid (paba), p-h2nc6h4(cooh), is used in some sunscreens and hair conditioning products. Calculate the ph of an aqueous solution with [paba] = 0. 030 m and ka = 2. 2 × 10-5

Answer 1

the pH of an aqueous solution with [paba] = 0. 030 m and ka = 2. 2 × 10⁻⁵

What is pH ?

pH is a measure of how acidic/basic water is.

The range goes from 0 - 14, with 7 being neutral.

pHs of less than 7 indicate acidity, whereas a pH of greater than 7 indicates a base.

pH is really a measure of the relative amount of free hydrogen and hydroxyl ions in the water.

H₂NC₆H₄COOH    ---->     H₂NC₆H₄COO⁻ +  H⁺

 0.030M                                0                       0

 0.030-x                                x                       x

$\rm K_{a}= \dfrac{[H^{+}][H_{2}NC_{6}H_{4}COO^{-} ]}{[H_{2}NC_{6}H_{4}COOH]}$

= x² / 0.030-x

x = 8.01 * 10⁻⁴

[H⁺] = x = 8.01 * 10⁻⁴

pH = -log[ H⁺]

=-log[ 8.01 * 10⁻⁴]

pH = 3.09

Therefore the pH of an aqueous solution with [paba] = 0. 030 m and ka = 2. 2 × 10⁻⁵