Periodic Table

Question 1

What is the reaction of sodium oxide with water, and the pH of its resulting solution?

Answer 1

Na2O is very soluble and gives a strong alkaline solution (pH ≈ 13) in water: Na2O (s) + H2O (l) → 2NaOH (aq)

Question 2

What is the reaction of magnesium oxide with water, and the pH of its resulting solution?

Answer 2

MgO is slightly soluble and gives a weakly alkaline solution (pH ≈ 9) in water: MgO (s) + H2O (l) ⇌ Mg(OH)2 (aq)

Question 3

What are the reactions of aluminium oxide and silicon dioxide with water, and the pH of their resulting solutions?

Answer 3

Al2O3 and SiO2 (because of strong covalent bonds holding the

macromolecular structure together) are insoluble in and do not react with water (pH = 7)

Question 4

What are the reactions of phosphorus (v) oxide and sulfur trioxide with water, and the pH of their resulting solutions?

Answer 4

P4O10 and SO3 react vigorously with water to give strongly acidic solutions (pH ≈ 1): P4O10 (s) + 6H2O (l) → 4H3PO4 (aq) 
and SO3 (g) + H2O (l) → H2SO4 (aq)

Question 5

What is the reaction of sodium chloride with water, and the pH of its resulting solution?

Answer 5

NaCl dissolves readily in water to form a neutral solution (pH = 7) of hydrated ions: NaCl (s) → Na+ (aq) + Cl− (aq)

Question 6

What is the reaction of magnesium chloride with water, and the pH of its resulting solution?

Answer 6

MgCl2 (ionic) hydrolyses slightly in water to give a slightly acidic solution (pH 6.5). MgCl2 (s) + 6H2O (l) → Mg(H2O)62+ (aq) + 2Cl− (aq)
and Mg(H2O)62+ (aq) + H2O (l) ⇌ Mg(H2O)5OH+ (aq) + H3O+ (aq)

Question 7

What is the reaction of aluminium chloride with water, and the pH of its resulting solution?

Answer 7

AlCl3 (covalent) hydrolyses in water to give an acidic solution (pH 3). AlCl3 (s) + 6H2O (l) → Al(H2O)63+ (aq) + 3Cl− (aq) 
and Al(H2O)63+ (aq) + H2O (l) ⇌ Al(H2O)5OH2+ (aq) + H3O+ (aq)

Question 8

What are the reactions of silicon tetrachloride and phosphorus pentachloride with water, and the pH of its resulting solutions?

Answer 8

SiCl4, PCl5 dissolve vigorously in water and are hydrolysed completely to give acidic solutions (pH 2) with the evolution of HCl gas. SiCl4 (l) + 2H2O (l) → SiO2 (s) + 4HCl (g)
and PCl5 (s) + 4H2O (l) → H3PO4 (aq) + 5HCl (g)