- In general, the salt that can make hydrolysis (both ions) is option c (ammonium nitrite).
- Salts that can make hydrolysis (one of the ions) are option a (potassium fluoride), option e (potassium cyanide), option f (sodium benzoate), option h (sodium carbonate) and option k (potassium formiate).
- Surely the neutrals salt are (salts that don't make hydrolysis) option b (sodium nitrate), option d (magnessium sulfate), option g (rubidium iodide) and option i (calcium chloride).
Explanation:
To determine the hydrolysis we have to dissociate the salts, and then we define the conjugate strong bases or acids, that can react to water.
a. KF → K⁺ + F⁻
F⁻ comes from the HF, a weak acid so the anion is the conjugate strong base. F⁻ can make hydrolysis, but the K⁺, can not.
b. NaNO₃ → Na⁺ + NO₃⁻
Boths are conjugate weak acid and base, this salt is neutral. So they cannot do hydrolysis.
c. NH₄NO₂ → NH₄⁺ + NO₂⁻
Both ions can make hydrolysis to water, because the are conjugate strong base and acid.
The ammonium gives ammonium again:
NH₄⁺ + H₂O ⇄ NH₃ + H₃O⁺ Ka
The nitrite gives nitrose acid, again
NO₂⁻ + H₂O ⇄ HNO₂ + OH⁻ Kb
d. MgSO₄ → Mg²⁺ + SO₄⁻²
This is a neutral salt. Boths are conjugate weak acid and base, that's why they can not make hydrolysis.
e. KCN → K⁺ + CN⁻
As K⁺ comes from a strong base, it can not do hydrolysis.
Then, the cyanide can make hydrolysis because it comes from the HCN (a weak acid), so the ion is the conjugate strong base.
CN⁻ + H₂O ⇄ HCN + OH⁻
f. C₆H₅COONa → C₆H₅COO⁻ + Na⁺
This salt is called sodium benzoate. As Na⁺ comes from a strong base, it can not do hydrolysis. Then, the C₆H₅COO⁻ can make hydrolysis because it comes from the benzoic acid, so the ion is the conjugate strong base.
C₆H₅COO⁻ + H₂O ⇄ C₆H₅COOH + OH⁻ Kb
g. RbI → Rb⁺ + I⁻
This is a neutral salt. Similar case as NaCl. Both are conjugate weak acid and base, that's why they can not make hydrolysis.
h. Na₂CO₃ → 2Na⁺ + CO₃⁻²
The one that can make hydrolysis in this case, is the carbonate anion.
CO₃⁻² + H₂O ⇄ HCO₃⁻ + OH⁻
Carbonate comes from the carbonic acid, a dyprotic weak one.
i. CaCl₂ → Ca²⁺ + 2Cl⁻
This is a neutral salt. Similar case as NaCl. Both are conjugate weak acid and base, that's why they can not make hydrolysis.
j. HCOOK → HCOO⁻ + K⁺
This is the potassium formiate. K⁺ comes from KOH, a strong base. It don't make hydrolysis, while the HCOO⁻ can do the hydrolysis in water.
When the formiate react, we can produce formic acid. Formiate is the conjugate strong base, of a weak acid.
HCOO⁻ + H₂O ⇄ HCOOH + OH⁻
