Mr Cole Chemistry

Neutralisation Reactions of Period 3 Oxides Questions

Neutralisation Reactions of Period 3 Oxides

Period 3 Worksheet
1. Tick the boxes in the table below stating whether the group 3 oxides will undergo the following reactions.
Na2O MgO Al2O3 SiO2 P4O10 SO2 SO3
Reacts with HCl
Reacts with NaOH
Reacts with H2O
Acts as an acid or base when reacting with H2O
Answer
Na2O MgO Al2O3 SiO2 P4O10 SO2 SO3
Reacts with HCl ✓ ✓ ✓
Reacts with NaOH ✓ ✓ ✓ ✓ ✓
Reacts with H2O ✓ ✓ ✓ ✓ ✓
Acts as an acid or base when reacting with H2O Base Base N/A N/A Acid Acid Acid
2. Write the equation(s) for the reactions of Na2O and state the conditions required for the reaction(s) to take place.

Reaction with Acid:

Na2O(s) + 2HCl(aq) → 2NaCl(aq) + H2O(l)

Reaction with Water:

Na2O(s) + H2O(l) → 2NaOH(aq)
3. Write the equation(s) for the reactions of MgO and state the conditions required for the reaction to take place.

Reaction with Acid:

MgO(s) + 2HCl(aq) → MgCl2(aq) + H2O(l)

Reaction with Water:

MgO(s) + H2O(l) → Mg(OH)2(aq)
4. Write the equation(s) for the reactions of Al2O3 and state the conditions required for the reaction(s) to take place.

Reaction with Acid (Heated):

Al2O3(s) + 6HCl(aq) → 2AlCl3(l) + 3H2O(l)

Reaction with Base (Heated strongly with NaOH):

Al2O3(s) + 2NaOH(aq) + 3H2O(l) → 2NaAl(OH)4(s)

Note: No reaction with water as it is insoluble.

5. Write the equation(s) for the reactions of SiO2 and state the conditions required for the reaction(s) to take place.

Reaction with Base (Hot, concentrated NaOH):

SiO2(s) + 2NaOH(aq) → Na2SiO3(s) + H2O(l)

Note: No reaction with water or acid.

6. Write the equation(s) for the reactions of P4O10 and state the conditions required for the reaction(s) to take place.

Reaction with Base (Violently with cold NaOH):

P4O10(s) + 12NaOH(aq) → 4Na3PO4(aq) + 6H2O(l)

Reaction with Water (Violently with cold water):

P4O10(s) + 6H2O(l) → 4H3PO4(aq)

Note: No reaction with acids as it is acidic itself.

7. Write the equation(s) for the reactions of SO2 and state the conditions required for the reaction(s) to take place.

Reaction with Water (Bubble gas through water):

SO2(g) + H2O(l) → H2SO3(aq)

Reaction with Base (Bubble gas through NaOH):

SO2(g) + 2NaOH(l) → Na2SO3(aq) + H2O(l)

Note: No reaction with acids as it is acidic itself.

8. Write the equation(s) for the reactions of SO3 and state the conditions required for the reaction(s) to take place.

Reaction with Water (Bubble gas through water):

SO3(g) + H2O(l) → H2SO4(aq)

Reaction with Base (Bubble gas through NaOH):

SO3(g) + 2NaOH(l) → Na2SO4(aq) + H2O(l)

Note: No reaction with acids as it is acidic itself.

9. The pH of the dissolved oxides is important.
a) State the pH of the period 3 oxides when they are dissolved in water.
Na2O MgO Al2O3 SiO2 P4O10 SO2 SO3
pH 14 10 N/A N/A 0 3 0
b) Explain the difference in alkalinity of Na2O and MgO.

Sodium oxide is more soluble than magnesium oxide (it reacts with water to form soluble sodium hydroxide more readily than magnesium oxide reacts to form magnesium hydroxide). This results in a higher concentration of OH– ions with sodium oxide, leading to a higher pH.

c) Explain the difference in acidity of P4O10 and SO2.

When P4O10 reacts with water, it forms phosphoric acid (H3PO4). When SO2 dissolves in water, it forms sulfurous acid (H2SO3). Phosphoric acid is a stronger acid than sulfurous acid, meaning it dissociates more fully in solution to release a higher concentration of H+ ions.

d) Explain the difference in acidity of SO2 and SO3.

These gases dissolve in water to form H2SO3 and H2SO4. The hydrogen atoms in H2SO4 dissociate more easily than those in H2SO3. This is due to the higher oxidation number on the sulfur in H2SO4, which pulls electron density in the O-H bonds towards the sulfur atom, weakening the O-H bond and stabilising the anion formed upon dissociation. This shifts the equilibrium more towards the dissociated form.

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