The gas evolved when sodium carbonate reacts with hydrochloric acid is ________.
Carbon dioxide
Understanding the Reaction: Sodium Carbonate and Hydrochloric Acid
This question asks about the gas produced when sodium carbonate reacts with hydrochloric acid. This is a classic example of a reaction between a metal carbonate and an acid.
When an acid reacts with a metal carbonate, the products typically formed are a salt, water, and carbon dioxide gas.
The reactants are sodium carbonate ($\text{Na}_2\text{CO}_3$) and hydrochloric acid ($\text{HCl}$).
The chemical equation for this reaction is:
$\text{Na}_2\text{CO}_3\text{(s)} + 2\text{HCl(aq)} \rightarrow 2\text{NaCl(aq)} + \text{H}_2\text{O(l)} + \text{CO}_2\text{(g)}$
Let's break down what happens:
- Sodium carbonate ($\text{Na}_2\text{CO}_3$) is a solid.
- Hydrochloric acid ($\text{HCl}$) is an aqueous solution.
- They react to form:
- Sodium chloride ($\text{NaCl}$), which is a salt dissolved in water (aqueous).
- Water ($\text{H}_2\text{O}$), which is a liquid.
- Carbon dioxide ($\text{CO}_2$), which is a gas.
The gas evolved, meaning the gas that bubbles out or is released, in this reaction is carbon dioxide ($\text{CO}_2$).
Why Other Options Are Incorrect
- Hydrogen ($\text{H}_2$): Hydrogen gas is usually produced when active metals (like sodium, zinc, or magnesium) react directly with acids. Carbonates do not produce hydrogen gas when reacting with acids.
- Chlorine ($\text{Cl}_2$): Chlorine gas is not a product of this specific reaction. It might be produced in other reactions involving chlorides, such as electrolysis or reactions with strong oxidizing agents.
- Hydrogen Chloride ($\text{HCl}$): Hydrogen chloride is the reactant acid itself, not a gas produced by the reaction. It is used up in the reaction with sodium carbonate.
Summary of the Sodium Carbonate and Hydrochloric Acid Reaction
Here is a quick summary of the reaction and its products:
| Reactant 1 | Reactant 2 | Products | Gas Evolved |
|---|---|---|---|
| Sodium Carbonate ($\text{Na}_2\text{CO}_3$) | Hydrochloric Acid ($\text{HCl}$) | Sodium Chloride ($\text{NaCl}$), Water ($\text{H}_2\text{O}$), Carbon Dioxide ($\text{CO}_2$) | Carbon Dioxide ($\text{CO}_2$) |
Therefore, the gas evolved when sodium carbonate reacts with hydrochloric acid is carbon dioxide.
Revision Table: Key Acid-Carbonate Reactions
| Reactants | General Equation | Products | Gas Evolved |
|---|---|---|---|
| Acid + Metal Carbonate | Acid + Carbonate > Salt + Water + Carbon Dioxide | Salt, Water, Carbon Dioxide | Carbon Dioxide ($\text{CO}_2$) |
| Example: $\text{HCl}$ + $\text{Na}_2\text{CO}_3$ | $2\text{HCl(aq)} + \text{Na}_2\text{CO}_3\text{(s)} \rightarrow 2\text{NaCl(aq)} + \text{H}_2\text{O(l)} + \text{CO}_2\text{(g)}$ | Sodium Chloride, Water, Carbon Dioxide | Carbon Dioxide ($\text{CO}_2$) |
| Example: $\text{HNO}_3$ + $\text{CaCO}_3$ | $2\text{HNO}_3\text{(aq)} + \text{CaCO}_3\text{(s)} \rightarrow \text{Ca(NO}_3)_2\text{(aq)} + \text{H}_2\text{O(l)} + \text{CO}_2\text{(g)}$ | Calcium Nitrate, Water, Carbon Dioxide | Carbon Dioxide ($\text{CO}_2$) |
Additional Information: Identifying Carbon Dioxide Gas
How can you test for carbon dioxide gas?
The standard test for carbon dioxide gas involves bubbling it through limewater, which is a solution of calcium hydroxide ($\text{Ca(OH)}_2$).
When carbon dioxide is bubbled through limewater, it reacts with calcium hydroxide to form insoluble calcium carbonate ($\text{CaCO}_3$), which is a white precipitate. This makes the limewater turn cloudy or milky.
The equation for this reaction is:
$\text{Ca(OH)}_2\text{(aq)} + \text{CO}_2\text{(g)} \rightarrow \text{CaCO}_3\text{(s)} + \text{H}_2\text{O(l)}$
This milky appearance is a positive test for the presence of carbon dioxide gas.
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