Hydrolysis of salts
Answers are for parents and teachers.
1
Write the first-step ionic hydrolysis equations for KNO₂ and Zn(NO₃)₂ and state the medium.
NO₂⁻ + H₂O ⇄ HNO₂ + OH⁻ (alkaline); Zn²⁺ + H₂O ⇄ ZnOH⁺ + H⁺ (acidic).
2
Group these salts by medium: NaBr, Na₃PO₄, Cu(NO₃)₂, K₂SO₄.
Neutral: NaBr, K₂SO₄; alkaline: Na₃PO₄; acidic: Cu(NO₃)₂.
3
Why does hydrolysis of FeCl₃ increase on dilution or boiling?
Hydrolysis is endothermic, so heating shifts the equilibrium toward the products (water also dissociates more). On dilution there is more water to react and the ions are farther apart, so the equilibrium again shifts toward hydrolysis.
4
75 g of Al₂S₃ is completely hydrolysed: Al₂S₃ + 6H₂O → 2Al(OH)₃↓ + 3H₂S↑. How many grams of Al(OH)₃ precipitate? (M(Al₂S₃) = 150 g/mol, M(Al(OH)₃) = 78 g/mol)
78
5
A soda (Na₂CO₃) solution is said to feel slippery. What is the reason? (Do not test it with your hands.)
The solution is alkaline (CO₃²⁻ hydrolysis gives OH⁻), and alkali saponifies fats.