Question

Write or complete the acid-base reaction that occurs for each of the following and label the conjugate acids and bases.

i. Methylamine (CH₃NH₂), an organic base, reacts with water.
CH₃NH₂ (aq) + H₂O (l) ⇌ CH₃NH₃⁺ (aq) + OH⁻ (aq)

ii. NH₄⁺ (aq) + CN⁻ (aq) ⇌
NH₄⁺ (aq) + CN⁻ (aq) ⇌ HCN (aq) + NH₃ (aq)

iii. The hydrogen oxalate ion (HC₂O₄⁻) acts as an acid in water.
HC₂O₄⁻ (aq) + H₂O (aq) ⇌ C₂O₄²⁻ + H₃O⁺ (aq)

Answer 1

In the provided acid-base reactions, methylamine reacts with water forming methylammonium ion and OH-, ammonium ion reacts with cyanide ion forming hydrogen cyanide and ammonia, and the hydrogen oxalate ion reacts with water forming oxalate ion and hydronium ion.

Step-by-step explanation:

When methylamine (CH₃NH₂), a weak base, reacts with water, the following acid-base reaction takes place:

CH₃NH₂ (aq) + H₂O (l) ⇌ CH₃NH₃⁺ (aq) + OH⁻ (aq)

In this reaction, methylamine (CH₃NH₂) accepts a proton (H+) from water, forming the methylammonium ion (CH₃NH₃⁺) and the hydroxide ion (OH⁻). The conjugate acid-base pairs are CH₃NH₂/CH₃NH₃⁺ and H₂O/OH⁻.

For the second part:

NH₄⁺ (aq) + CN⁻ (aq) ⇌ HCN (aq) + NH₃ (aq)

Here, NH₄⁺ (ammonium ion) donates a proton to CN⁻ (cyanide ion), forming HCN (hydrogen cyanide) and NH₃ (ammonia). The conjugate acid-base pairs are NH₄⁺/NH₃ and CN⁻/HCN.

Lastly, for the hydrogen oxalate ion acting as an acid in water:

HC₂O₄⁻ (aq) + H₂O (l) ⇌ C₂O₄²⁻ (aq) + H₃O⁺ (aq)

The hydrogen oxalate ion (HC₂O₄⁻) donates a proton to water, forming the oxalate ion (C₂O₄²⁻) and the hydronium ion (H₃O⁺). The conjugate acid-base pairs are HC₂O₄⁻/C₂O₄²⁻ and H₂O/H₃O⁺.