A protein 'A' contains 0.30% of glycine (molecular weight 75). The minimum molar mass of the protein 'A' is __________ × 10³ g mol⁻¹ [nearest integer]

Solution

Chemistry ma’am · 3 steps

Minimum molar mass means the smallest possible molecule, and that molecule holds just one glycine.

1. Why minimum. Each protein molecule must contain at least one whole glycine unit. The molecule is lightest when it has exactly one, so that case gives the minimum molar mass.
2. Set up the percentage. With one glycine per molecule, one mole of protein contains 75 g of glycine. This 75 g must be 0.30% of the protein's molar mass M.

   0.30/100 × M = 75 ⇒ M = (75 × 100)/0.30 = 25000 g mol⁻¹

3. So. M = 25 × 10³ g mol⁻¹, so the answer is 25.

The common slip: 25000. Entering the full molar mass gives 25000, but the blank already carries × 10³, so the entry is 25.

The idea to keep. For the minimum molar mass, put exactly one unit of the smallest component in each molecule. Then that component's mass divided by its mass fraction gives the molar mass.

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