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Acids and Bases - Tests for Ions and Gases (H2 and CO2)

Grade 9IB

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Hydrogen gas (H2H_{2}) is identified using the 'squeaky pop' test. When a lighted splint is held at the mouth of a test tube containing the gas, the hydrogen reacts explosively with oxygen to produce water vapor and a characteristic sound: 2H2(g)+O2(g)→2H2O(g)2H_{2}(g) + O_{2}(g) \rightarrow 2H_{2}O(g).

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Carbon dioxide gas (CO2CO_{2}) is identified using the limewater test. When CO2CO_{2} is bubbled through limewater (aqueous calcium hydroxide, Ca(OH)2Ca(OH)_{2}), it reacts to form an insoluble white precipitate of calcium carbonate (CaCO3CaCO_{3}), which turns the limewater milky or cloudy.

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The reaction between an acid and a reactive metal (such as MgMg, ZnZn, or FeFe) typically produces a salt and hydrogen gas: Acid+Metal→Salt+H2(g)Acid + Metal \rightarrow Salt + H_{2}(g).

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The reaction between an acid and a metal carbonate or metal hydrogen carbonate produces a salt, water, and carbon dioxide gas: Acid+Carbonate→Salt+H2O(l)+CO2(g)Acid + Carbonate \rightarrow Salt + H_{2}O(l) + CO_{2}(g).

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Acids are substances that release hydrogen ions (H+H^{+}) in aqueous solutions, while bases (specifically alkalis) release hydroxide ions (OH−OH^{-}) or accept H+H^{+} ions.

📐Formulae

2HCl(aq)+Mg(s)→MgCl2(aq)+H2(g)2HCl(aq) + Mg(s) \rightarrow MgCl_{2}(aq) + H_{2}(g) (Reaction producing Hydrogen)

H2SO4(aq)+CaCO3(s)→CaSO4(aq)+H2O(l)+CO2(g)H_{2}SO_{4}(aq) + CaCO_{3}(s) \rightarrow CaSO_{4}(aq) + H_{2}O(l) + CO_{2}(g) (Reaction producing Carbon Dioxide)

CO2(g)+Ca(OH)2(aq)→CaCO3(s)+H2O(l)CO_{2}(g) + Ca(OH)_{2}(aq) \rightarrow CaCO_{3}(s) + H_{2}O(l) (Limewater Test Equation)

2H2(g)+O2(g)→2H2O(g)2H_{2}(g) + O_{2}(g) \rightarrow 2H_{2}O(g) (Hydrogen Combustion)

💡Examples

Problem 1:

A student adds dilute Sulfuric acid (H2SO4H_{2}SO_{4}) to Zinc granules (ZnZn). State the name of the gas produced and the observation that would confirm its identity.

Solution:

The gas produced is Hydrogen (H2H_{2}). A lighted splint held at the mouth of the test tube will produce a 'squeaky pop' sound.

Explanation:

The chemical reaction is Zn(s)+H2SO4(aq)→ZnSO4(aq)+H2(g)Zn(s) + H_{2}SO_{4}(aq) \rightarrow ZnSO_{4}(aq) + H_{2}(g). The 'pop' sound occurs because hydrogen gas is highly flammable and reacts rapidly with oxygen in the air.

Problem 2:

During an experiment, a gas is evolved by reacting Magnesium Carbonate (MgCO3MgCO_{3}) with Hydrochloric acid (HClHCl). When this gas is passed through a clear solution of limewater, the solution turns cloudy. Identify the gas and write the chemical equation for the gas production.

Solution:

The gas is Carbon dioxide (CO2CO_{2}). Equation: MgCO3(s)+2HCl(aq)→MgCl2(aq)+H2O(l)+CO2(g)MgCO_{3}(s) + 2HCl(aq) \rightarrow MgCl_{2}(aq) + H_{2}O(l) + CO_{2}(g).

Explanation:

Carbonates react with acids to release carbon dioxide gas. The cloudiness in limewater is due to the formation of calcium carbonate (CaCO3CaCO_{3}), which is a white solid precipitate.