Hemoglobin contains 0.34 % of iron by mass. The number of Fe atoms in 3.3 g of hemoglobin is
(Given: Atomic mass of Fe is 56 u, N_A=6.022 × 10²³ mol⁻¹.)

Solution

Chemistry ma’am · 3 steps

Pull out the iron's mass first, then turn grams into moles and moles into atoms.

1. Mass of iron. Iron is 0.34% of the hemoglobin by mass, so the iron in 3.3 g is 0.34/100 × 3.3 = 0.01122 g.
2. Moles of iron. Divide by the molar mass of Fe: 0.01122/56 = 2.004 × 10⁻⁴ mol.

   N = 2.004 × 10⁻⁴ × 6.022 × 10²³ = 1.207 × 10²⁰

3. So. The sample holds about 1.21 × 10²⁰ Fe atoms, which is option (c).

The idea to keep. For atoms of one element inside a compound, find that element's mass from the percentage, divide by its own atomic mass, then multiply by N_A.

Answer from the NTA final answer key. Solution by PrepWiser.