Question

A mixture of sodium oxide and calcium oxide are dissolved in water and saturated with excess carbon dioxide gas. The resulting solution is \(\ldots \ldots \ldots \ldots\) It contains ..... (a) Acidic \(\mathrm{NaOH}\) and \(\mathrm{CaCO}_{3}\) (b) Basic \(\mathrm{Na}_{2} \mathrm{CO}_{3}\) and \(\mathrm{CaCO}_{3}\) (c) Neutral \(\mathrm{Na}_{2} \mathrm{CO}_{3}\) and \(\mathrm{CaCO}_{3}\) (d) Basic \(\mathrm{NaOH}\) and \(\mathrm{Ca}(\mathrm{OH})_{2}\)

Short answer

The resulting solution is basic with \(\mathrm{Na}_2 \mathrm{CO}_3\) and \(\mathrm{CaCO}_3\).

Step-by-step solution

Understand the Reaction

When sodium oxide (Na2O) and calcium oxide (CaO) are dissolved in water, they form sodium hydroxide (NaOH) and calcium hydroxide (Ca(OH)2) respectively through the reactions: \( Na_2O + H_2O \rightarrow 2 NaOH \) and \( CaO + H_2O \rightarrow Ca(OH)_2 \).

Reaction with Carbon Dioxide

Both NaOH and Ca(OH)2 can react with excess carbon dioxide (CO2). The reactions are: \( 2 NaOH + CO_2 \rightarrow Na_2CO_3 + H_2O \) and \( Ca(OH)_2 + CO_2 \rightarrow CaCO_3 + H_2O \).

Determine Products of the Reactions

From the reactions in the previous step, we can see that the products formed are sodium carbonate (Na2CO3) and calcium carbonate (CaCO3).

Analyze the Nature of Products

Sodium carbonate (Na2CO3) is a basic salt and calcium carbonate (CaCO3) is generally neutral or slightly basic under typical conditions.

Key concepts

Sodium Oxide Reactions

When sodium oxide \((Na_2O)\) is introduced to water, it undergoes a chemical reaction to form sodium hydroxide \((NaOH)\). This reaction can be represented by the equation:

• \(Na_2O + H_2O \rightarrow 2 NaOH \)

This reaction is characterized as a basic reaction because sodium hydroxide is a strong base. Different oxides show various characteristics depending on their original element. Sodium, which is an alkali metal, forms basic oxides. This reaction forms hydroxides, which increase the pH of the solution, making it basic.

Calcium Oxide Reactions

Calcium oxide \((CaO)\), like sodium oxide, forms hydroxides upon reaction with water. The chemical equation for this reaction is:

• \(CaO + H_2O \rightarrow Ca(OH)_2 \)

Calcium hydroxide \((Ca(OH)_2)\) is also a base, but it is a slightly weaker base compared to sodium hydroxide. Calcium oxide is classified as an alkaline earth metal oxide. When such oxides react with water, they also result in hydroxides, increasing the basicity of the solution. Hence, both sodium and calcium oxides contribute to the basic nature when dissolved in water.

Carbon Dioxide Reactions

Carbon dioxide \((CO_2)\) is an acidic oxide, which reacts with bases to form carbonates. When carbon dioxide is added to a solution containing \(NaOH\) and \(Ca(OH)_2\), it reacts as follows:

• \(2NaOH + CO_2 \rightarrow Na_2CO_3 + H_2O \)
• \(Ca(OH)_2 + CO_2 \rightarrow CaCO_3 + H_2O \)

Through these reactions, \(Na_2CO_3\) (sodium carbonate) and \(CaCO_3\) (calcium carbonate) are formed. Sodium carbonate remains soluble and exhibits basic properties, while calcium carbonate, due to its lower solubility, can precipitate out of solution. This interaction is essential for controlling the levels of CO2 and maintaining a balanced solution pH, which will be explored next.

Solution pH Analysis

The analysis of the solution's pH after reactions have occurred involves understanding the nature of the resulting compounds.

• Sodium Carbonate\((Na_2CO_3)\): This compound is basic because it originates from a strong base \((NaOH)\) and a weak acid \((H_2CO_3)\). It increases the pH, making the solution basic.
• Calcium Carbonate \((CaCO_3)\): This salt is generally considered neutral because it is poorly soluble in water. It does not significantly alter the pH, rendering it fairly inert in terms of pH change.

Given these properties, the solution, after bubbling CO2 through \(NaOH\) and \(Ca(OH)_2\), tends toward basicity, primarily due to the presence of soluble sodium carbonate. Calcium carbonate's neutrality and limited solubility ensure it doesn't counteract this effect significantly.