JEE Main · 2022 · Shift-IIeasyMOLE-127

Hemoglobin contains 0.34\% of iron by mass. The number of Fe atoms in 3.3\,g of hemoglobin is: (Atomic mass of Fe =…

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

Question

Hemoglobin contains 0.34%0.34\% of iron by mass. The number of Fe atoms in 3.3 g3.3\,\text{g} of hemoglobin is: (Atomic mass of Fe =56 u= 56\,\text{u}, NA=6.022×1023 mol−1N_A = 6.022 \times 10^{23}\,\text{mol}^{-1})

Options
  1. a

    1.21×1051.21 \times 10^{5}

  2. b

    12.0×101612.0 \times 10^{16}

  3. c

    1.21×10201.21 \times 10^{20}

    ✓
  4. d

    3.4×10223.4 \times 10^{22}

Correct Answerc

1.21×10201.21 \times 10^{20}

Detailed Solution

🧠 Iron is a tiny fraction of haemoglobin You don't need haemoglobin's molar mass. The percentage of iron alone gives you the mass of Fe inside the sample. Convert that mass to moles, then to atoms using NAN_A.

🗺️ Three steps Mass of Fe in 3.3 g3.3\,\text{g} of haemoglobin: mFe=0.0034×3.3=0.01122 g.m_{Fe} = 0.0034 \times 3.3 = 0.01122\,\text{g}. Moles of Fe: n=0.0112256≈2.003×10−4 mol.n = \frac{0.01122}{56} \approx 2.003 \times 10^{-4}\,\text{mol}. Atoms of Fe: N=2.003×10−4×6.022×1023≈1.21×1020.N = 2.003 \times 10^{-4} \times 6.022 \times 10^{23} \approx 1.21 \times 10^{20}.

⚠️ Common mistake Using 0.340.34 instead of 0.00340.0034 for the percentage. 0.34%0.34\% means 0.34/100=0.00340.34/100 = 0.0034 as a fraction.

Answer: (c)\boxed{\text{Answer: (c)}}

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