Concept Explanation: Reaction of Zinc with Acids and Bases

Zinc is an amphoteric metal, meaning it reacts with both acids and bases to produce hydrogen gas. Let's analyze the reactions step by step.

Step 1: Write the Balanced Chemical Equations

(a) Reaction with dilute hydrochloric acid (HCl):

Zinc reacts with HCl to form zinc chloride and hydrogen gas.

$\mathrm{Zn}+2\mathrm{HCl}\to \mathrm{ZnCl}{2}_{}+H_2$

From the equation: 1 mole of Zn produces 1 mole of H₂.

(b) Reaction with aqueous sodium hydroxide (NaOH):

Zinc reacts with NaOH to form sodium zincate and hydrogen gas.

$\mathrm{Zn}+2\mathrm{NaOH}\to \mathrm{Na}{2}_{}\mathrm{ZnO}{2}_{}+H_2$

From the equation: 1 mole of Zn produces 1 mole of H₂.

Step 2: Determine Moles of Zinc Given

Mass of zinc = 5 g

Molar mass of Zn = 65 g/mol

Moles of Zn = $\frac{5}{65}$ mol

Step 3: Calculate Moles of H₂ Produced in Each Reaction

From both equations, the mole ratio of Zn to H₂ is 1:1.

So, moles of H₂ from reaction (a) = $\frac{5}{65}$ mol

Moles of H₂ from reaction (b) = $\frac{5}{65}$ mol

Step 4: Find the Ratio of Volumes of H₂ Evolved

Since the number of moles of H₂ produced is the same in both reactions, and volume of gas is directly proportional to number of moles (at same temperature and pressure), the volumes will be equal.

Therefore, the ratio of volumes is 1 : 1.

Final Answer

The ratio of the volumes of H₂ evolved is 1 : 1.

Related Topics

• Amphoteric Metals: Metals that react with both acids and bases (e.g., Zn, Al).
• Stoichiometry: Calculation of reactants and products in chemical reactions.
• Mole Concept: Relating mass to number of particles or volume of gas.

Important Formulae and Theory

• Number of moles = $\frac{\mathrm{Mass}}{\mathrm{Molar}\mathrm{mass}}$
• At STP, 1 mole of any gas occupies 22.4 L.
• For gases, volume ratio = mole ratio (at constant T and P).
• Zinc with acid: $\mathrm{Zn}+2H+\to \mathrm{Zn}{2}^{+}+H_2$
• Zinc with base: $\mathrm{Zn}+2\mathrm{OH}-\to \mathrm{ZnO}{2}_2^{-}+H_2$