Question

A certain amount of a metal whose equivalent mass is 28 displaces $0.7 \mathrm{L}$ of $\mathrm{H}_2$ at STP from an acid. Hence, mass of the element is

• A. $1.75 \mathrm{g}$
• B. $0.875 \mathrm{g}$
• C. $3.50 \mathrm{g}$
• D. $7.00 \mathrm{g}$

Hint:

Equivalent mass = $\frac{\text{mass of metal}}{\text{mass of hydrogen displaced}} \times 1$.

Answer 1

The Correct Option is A

Step 1: Conceptual Understanding:
Equivalent mass = $\frac{\text{mass of metal}}{\text{mass of hydrogen displaced}} \times 1$.
Step 2: Explanation in Detail:
At STP, $0.7$ L of $\mathrm{H_2} = \frac{0.7}{22.4} = 0.03125$ mol $\mathrm{H_2}$. Mass of $\mathrm{H_2} = 0.03125 \times 2 = 0.0625$ g. Equivalent mass of metal = $28 = \frac{m}{0.0625} \Rightarrow m = 1.75$ g.
Step 3: Therefore, Stating the Final Answer
The mass of the element is $1.75$ g.