Answer:
A. Neutral salts. (7, 2)
B. Acidic salts. (4, 6)
C. Basic salts. (1, 3, 5)
Explanation:
We must know where, do the ions come from. If they come from a weak acid or base, they can make hydrolysis in water, so OH⁻ and H⁺ are given to medium.
1. LiF → Li⁺ + F⁻
F⁻ + H₂O ⇄ HF + OH⁻
F⁻ can make the hydrolysis, and it gives OH⁻. Salt is basic.
2. SrBr₂ → Sr²⁺ + 2Br⁻
Both are weak and they can not hydrolyse. This salt is neutral.
3. NH₄CN → NH₄⁺ + CN⁻
Both ions are strong, so they can make the hydrolysis. The thing is, while the ammonium gives protons, the cyanide give hydroxides. To determine how's the salt, we need to compare the Ka and Kb.
NH₄⁺ + H₂O ⇄ NH₃ + H₃O⁺ Ka = 5.7×10⁻¹⁰
CN⁻ + H₂O ⇄ HCN + OH⁻ Kb = 1.61×10⁻⁵
As Kb > Ka, pH is basic.
If Ka > Kb, pH would be acidic.
4. NH₄Br → NH₄ + Br⁻
Br⁻ does not hydrolize. The ammonium cation, reacts in water to give protons to medium that's why the salt will be acidic.
NH₄⁺ + H₂O ⇄ NH₃ + H₃O⁺ Ka
5. KCN → K⁺ + CN⁻
K⁺ does not hydrolize. The cyanide anion, reacts in water to give hydroxides to medium that's why the salt will be basic.
CN⁻ + H₂O ⇄ HCN + OH⁻ Kb
6. NH₄ClO₄ → NH₄⁺ + ClO₄⁻
ClO₄⁻ comes from the perchlroric acid (a strong acid). It does not hydrolyze
NH₄⁺ + H₂O ⇄ NH₃ + H₃O⁺ Ka
Ammonium gives H⁺ to medium so the salt is acidic.
7. LiNO₃ → Li⁺ + NO₃⁻
Both ions does not make hydrolysis. They come from a strong base and a strong acid, so they are the conjugate weak acid and base, respectively.
The salt in this case, will be neutral.
