2001 AIPMT Some Basic Concepts of ChemistryPercentage Composition and Molecular Mass Easy Question 47 of 49 in Some Basic Concepts of Chemistry

Percentage of Se in peroxidase anhydrous enzyme is 0.5% by weight (at. wt = 78.4) then minimum molecular weight of peroxidase anhydrous enzyme is : -

A $1.568 \times 10^4$
B $1.568 \times 10^3$
C 15.68
D $2.136 \times 10^4$

The answer is A.

Solution

0.5 percent Se by weight means 0.5 g of Se is present in 100 g of the enzyme.
For the minimum molecular weight, one molecule of the enzyme must contain at least one Se atom, i.e. 78.4 g of Se per mole.
Mass of enzyme containing 78.4 g Se $= \dfrac{100}{0.5} \times 78.4 = 15680$ g
So the minimum molecular weight is $1.568 \times 10^4$.

Concept Minimum molar mass from one atom

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