For the following acids:
i. CH3COOH
ii. HNO2
iii. HCN
a) What is the dissociation equation in an aqueous solution?
b)Give the KA expression for each of the acids.
c)Identify the acid-base pairs.
a)CH3COOH + H2O ==> CH3COO^- + H3O^+
b) Ka = (H3O^+)(CH3COO^-)/(CH3COOH)
c) CH3COOH is the acid/CH3COO^- is the base. H2O is the base/H3O^+ is the acid.
The others are done the same way. Just remember the definition of a Bronsted-Lowry acid/base and you can't go wrong.
To answer these questions, we need to understand the dissociation of acids in aqueous solutions.
a) The dissociation equation for an acid in an aqueous solution involves the ionization of the acid to produce hydrogen ions (H+) or hydronium ions (H3O+). The general form of the dissociation equation for an acid HA is:
HA(aq) ⇌ H+(aq) + A-(aq)
i. CH3COOH is a weak acid, also known as acetic acid. So, its dissociation equation can be written as:
CH3COOH(aq) ⇌ H+(aq) + CH3COO-(aq)
ii. HNO2 is also a weak acid, known as nitrous acid. Its dissociation equation can be written as:
HNO2(aq) ⇌ H+(aq) + NO2-(aq)
iii. HCN is a weak acid, known as hydrocyanic acid. Its dissociation equation can be written as:
HCN(aq) ⇌ H+(aq) + CN-(aq)
b) The KA expression for each acid represents the acid dissociation constant and provides information about the extent of an acid's ionization. The general expression for KA is:
KA = [H+][A-] / [HA]
i. For CH3COOH, its KA expression is:
KA = [H+][CH3COO-] / [CH3COOH]
ii. For HNO2, its KA expression is:
KA = [H+][NO2-] / [HNO2]
iii. For HCN, its KA expression is:
KA = [H+][CN-] / [HCN]
c) Acid-base pairs are formed according to the transfer of a proton (H+ ion) from the acid to the base. For each acid, the acid-base pairs are:
i. CH3COOH:
- Acid: CH3COOH (acetic acid)
- Base: CH3COO- (the conjugate base of acetic acid)
ii. HNO2:
- Acid: HNO2 (nitrous acid)
- Base: NO2- (the conjugate base of nitrous acid)
iii. HCN:
- Acid: HCN (hydrocyanic acid)
- Base: CN- (the conjugate base of hydrocyanic acid)
These acid-base pairs are connected by the transfer of a proton during the acid dissociation process.