Edexcel International A Level (IAL) Chemistry (YCH11) - Unit 2 - 8.14 Reactions of oxides and hydroxides-Study Notes - New Syllabus
Edexcel International A Level (IAL) Chemistry (YCH11) -Unit 2 – 8.14 Reactions of oxides and hydroxides- Study Notes- New syllabus
Edexcel International A Level (IAL) Chemistry (YCH11) -Unit 2 – 8.14 Reactions of oxides and hydroxides- Study Notes -International A Level (IAL) Chemistry (YCH11) – per latest Syllabus.
Key Concepts:
8.14 know the reactions of:
i oxides of Group 1 and 2 elements with water and dilute acid
ii hydroxides of Group 1 and 2 elements with dilute acid
Edexcel International A Level (IAL) Chemistry (YCH11) -Concise Summary Notes- All Topics
8.14 (i) Reactions of Oxides of Group 1 and Group 2
Oxides of Group 1 and Group 2 elements are basic oxides. They react with water to form hydroxides and with dilute acids to form salts and water.
(A) Reaction with Water
Group 1 Oxides
\( \mathrm{Na_2O + H_2O \rightarrow 2NaOH} \)
- Forms alkaline solution.
- Reaction is vigorous.
Group 2 Oxides
\( \mathrm{CaO + H_2O \rightarrow Ca(OH)_2} \)
- Reaction is exothermic.
- Forms slightly soluble hydroxide (alkaline).
Trend
- Reactivity increases down both groups.
- Group 1 oxides react more vigorously than Group 2.
(B) Reaction with Dilute Acids
Both Group 1 and Group 2 oxides react with acids to form salt + water.
Group 1 Example
\( \mathrm{Na_2O + 2HCl \rightarrow 2NaCl + H_2O} \)
Group 2 Example
\( \mathrm{MgO + 2HCl \rightarrow MgCl_2 + H_2O} \)
Explanation
- Oxides are basic.
- They neutralise acids.
- Produce salt and water (neutralisation reaction).
Comparison
- Group 1 oxides are more soluble → stronger alkaline solutions.
- Group 2 oxides are less soluble → weaker alkaline solutions.
Summary
- Oxides react with water → hydroxides.
- Oxides react with acids → salt + water.
- All are basic oxides.
Therefore, Group 1 and Group 2 oxides show typical basic behaviour in reactions with water and acids.
Example 1 :
Explain why sodium oxide forms a strongly alkaline solution in water.
▶️ Answer/Explanation
Sodium oxide reacts with water to form sodium hydroxide.
\( \mathrm{NaOH} \) is highly soluble.
Produces high concentration of \( \mathrm{OH^-} \) ions.
Therefore, solution is strongly alkaline.
Example 2 :
Explain why magnesium oxide produces a less alkaline solution than sodium oxide.
▶️ Answer/Explanation
Magnesium hydroxide is only slightly soluble.
Fewer \( \mathrm{OH^-} \) ions are produced.
Sodium hydroxide is highly soluble.
Therefore, sodium oxide forms a more alkaline solution.
8.14 (ii) Reactions of Hydroxides of Group 1 and Group 2 with Dilute Acids
Hydroxides of Group 1 and Group 2 are bases (alkalis if soluble) and react with dilute acids in neutralisation reactions to form salt and water.
General Equation
\( \mathrm{Metal\ hydroxide + Acid \rightarrow Salt + H_2O} \)
(A) Group 1 Hydroxides
Group 1 hydroxides (e.g. \( \mathrm{NaOH}, \mathrm{KOH} \)) are highly soluble strong alkalis.
Example
\( \mathrm{NaOH + HCl \rightarrow NaCl + H_2O} \)
- Reaction is fast and complete.
- Strong base + strong acid → strong neutralisation.
(B) Group 2 Hydroxides
Group 2 hydroxides (e.g. \( \mathrm{Mg(OH)_2}, \mathrm{Ca(OH)_2} \)) are less soluble but still basic.
Example
\( \mathrm{Ca(OH)_2 + 2HCl \rightarrow CaCl_2 + 2H_2O} \)
- Reaction may be slower if hydroxide is not fully soluble.
Ionic Equation
\( \mathrm{H^+(aq) + OH^-(aq) \rightarrow H_2O(l)} \)
- Shows essence of neutralisation.
Trends and Observations
Group 1 hydroxides:
- Highly soluble → strong alkaline solutions
- Rapid neutralisation
Group 2 hydroxides:
- Solubility increases down group
- More reactive down the group
Explanation
- Hydroxides provide \( \mathrm{OH^-} \) ions.
- Acids provide \( \mathrm{H^+} \) ions.
- These combine to form water.
Summary
- Hydroxides react with acids → salt + water.
- Group 1 hydroxides react more readily due to higher solubility.
- All reactions are neutralisation reactions.
Therefore, hydroxides of both groups behave as bases and neutralise acids effectively.
Example 1 :
Explain why sodium hydroxide reacts more rapidly with hydrochloric acid than magnesium hydroxide.
▶️ Answer/Explanation
Sodium hydroxide is highly soluble.
Produces more \( \mathrm{OH^-} \) ions in solution.
Magnesium hydroxide is sparingly soluble.
Therefore, reaction is slower for Mg(OH)\(_2\).
Example 2 :
Write the balanced equation for the reaction between barium hydroxide and nitric acid.
▶️ Answer/Explanation
\( \mathrm{Ba(OH)_2 + 2HNO_3 \rightarrow Ba(NO_3)_2 + 2H_2O} \)