JEE Main · 2023 · Shift-ImediumMOLE-136

A metal chloride contains 55.0\% of chlorine by weight. 100\,mL vapours at STP weigh 0.57\,g. The molecular formula of…

Some Basic Concepts (Mole Concept) · Class 11 · JEE Main Previous Year Question

Question

A metal chloride contains 55.0%55.0\% of chlorine by weight. 100 mL100\,\text{mL} vapours at STP weigh 0.57 g0.57\,\text{g}. The molecular formula of the metal chloride is: (At. mass Cl =35.5 u= 35.5\,\text{u})

Options
  1. a

    \ceMCl4\ce{MCl4}

  2. b

    \ceMCl3\ce{MCl3}

  3. c

    \ceMCl2\ce{MCl2}

    ✓
  4. d

    \ceMCl\ce{MCl}

Correct Answerc

\ceMCl2\ce{MCl2}

Detailed Solution

🧠 Molar mass from gas density At STP, 22,400 mL22{,}400\,\text{mL} of any gas weighs one molar mass. Scale up the 100 mL100\,\text{mL} weight to 22,400 mL22{,}400\,\text{mL} to get MM. Then 55%55\% of MM tells you the mass of chlorine, and dividing by 35.535.5 gives the number of Cl atoms.

🗺️ Three steps Molar mass: M=0.57100×22400≈127.7 g/mol.M = \frac{0.57}{100} \times 22400 \approx 127.7\,\text{g/mol}. Mass of Cl per mole =0.55×127.7≈70.2 g= 0.55 \times 127.7 \approx 70.2\,\text{g}. Number of Cl atoms =70.2/35.5≈2= 70.2 / 35.5 \approx 2.

So the formula is \ceMCl2\ce{MCl2}.

⚠️ Common mistake Computing only the molar mass and stopping. You also need the chlorine percentage to fix the formula.

Answer: (c)\boxed{\text{Answer: (c)}}

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