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Some Basic Concepts of Chemistry question

2023 · 12 Apr · Shift 1 · Q7

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Some Basic Concepts of Chemistry
2023 · 12 Apr · Shift 1 · Q7

Some Basic Concepts of Chemistry question

2023 · 12 Apr · Shift 1 · Q7

JEE MainChemistrySome Basic Concepts of ChemistryMCQ+4 / −1

A metal chloride contains

55.0 \%

of chlorine by weight .

100 \mathrm{~mL}

vapours of the metal chloride at STP weigh

0.57 \mathrm{~g}

. The molecular formula of the metal chloride is (Given: Atomic mass of chlorine is

35.5 \mathrm{u}

)

A
$\mathrm{MCl}_{2}$
B
$\mathrm{MCl}_{4}$
C
$\mathrm{MCl}_{3}$
D
$\mathrm{MCl}$

View written solutionFree

Correct answer: A

Find molar mass of the metal chloride from vapour data

At STP, $1$ mole of any gas occupies $22.4 \text{ L} = 22400 \text{ mL}$ .

Given:

Volume of vapour $= 100 \text{ mL}$
Mass of $100 \text{ mL}$ vapour $= 0.57 \text{ g}$

So, molar mass is

M = 0.57 \times \frac{22400}{100}

M = 0.57 \times 224 = 127.68 \text{ g mol}^{-1}

Thus, molecular mass of the metal chloride $\approx 127.7$ .

Use percentage of chlorine

The compound contains $55.0\%$ chlorine by mass.

So mass of chlorine in one mole of compound is

0.55 \times 127.68 = 70.224 \text{ g}

Since atomic mass of chlorine is $35.5$ , number of chlorine atoms is

\frac{70.224}{35.5} \approx 1.98 \approx 2

Hence, the formula must be

\mathrm{MCl}_2

Check metal mass

Mass of metal in one mole of compound:

127.68 - 2(35.5) = 127.68 - 71 = 56.68

This is reasonable for a metal atomic mass, so $\mathrm{MCl}_2$ is consistent.

Evaluate options

A: $\mathrm{MCl}_2$ ✅ Matches calculation
B: $\mathrm{MCl}_4$ ❌ Would require much higher chlorine percentage
C: $\mathrm{MCl}_3$ ❌ Chlorine atoms do not match
D: $\mathrm{MCl}$ ❌ Chlorine percentage too low

Therefore, the molecular formula is

\boxed{\mathrm{MCl}_2}

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