Classifying Acid and Base Strength from the Chemical Formula

Problem Classify each of the following compounds as a strong acid, weak acid, strong base, or weak base, and write the $K_a$ expression for any weak acid:

(a) KOH (b) $(CH_3)_2CHCOOH$ (c) $H_2SeO_4$ (d) $(CH_3)_2CHNH_2$

Question

Classifying Acid and Base Strength from the Chemical Formula

Problem Classify each of the following compounds as a strong acid, weak acid, strong base, or weak base, and write the [latex]K_a[/latex] expression for any weak acid:

(a) KOH (b) [latex](CH_3)_2CHCOOH[/latex] (c) [latex]H_2SeO_4[/latex] (d) [latex](CH_3)_2CHNH_2[/latex]

Accepted Answer

Plan We examine the formula and classify each compound as acid or base, using the text descriptions. Particular points to note for acids are the numbers of O atoms relative to ionizable H atoms and the presence of the —COOH group. For bases, we note the nature of the cation or the presence of an N atom that has a lone pair.

Solution (a) Strong base: KOH is one of the Group 1A(1) hydroxides.
(b) Weak acid: [latex](CH_3)_2CHCOOH[/latex] is a carboxylic acid, as indicated by the —COOH group; the dissociation reaction is:

[latex] (CH_3)_2CHCOOH(aq) + H_2O(l) \xrightleftharpoons[] H_3O^+(aq) + (CH_3)_2CHCOO^−(aq)[/latex]
and
[latex] Ka = \frac{[H_3O^+][(CH_3)_2CHCOO^−]}{[(CH_3)_2CHCOOH]}[/latex]
(c) Strong acid: [latex]H_2SeO_4[/latex] is an oxoacid in which the number of O atoms exceeds the number of ionizable protons by 2.
(d) Weak base: [latex](CH_3)_2CHNH_2[/latex] has a lone electron pair on the N and is an amine.

Chapter 18

Q. 18.1

Q. 18.1

Step-by-Step

Verified Solution