Answer:
CH₃NH₃⁺ is a weak acid.
HPO₄²⁻ has a negligible acidity.
CH₄ has a negligible acidity.
HNO₂ is a weak acid.
Explanation:
There are 7 strong acids: HCl, HBr, HI, HNO₃, H₂SO₄, HClO₃, HClO₄. The rest of the acids are weak.
CH₃NH₃⁺ is a weak acid, according to the following equation:
CH₃NH₃⁺ ⇄ CH₃NH₂ + H⁺
HPO₄²⁻ can act as an acid or as a base:
<u>Acid reaction:</u> HPO₄²⁻ ⇄ PO₄³⁻ + H⁺
<u>Basic reaction:</u> HPO₄² + H₂O ⇄ H₂PO₄⁻ + OH⁻
Given Kb > Ka, HPO₄²⁻ has a negligible acidity.
CH₄ cannot release nor accept H⁺ so it has a negligible acidity.
HNO₂ is a weak acid, according to the following reaction:
HNO₂ ⇄ H⁺ + NO₂⁻
