Question

Mole fraction of H$_2$SO$_4$ in aqueous solution is 0.9. Find mass % of H$_2$SO$_4$. (H=1, S=32, O=16 u)

• A. 90
• B. 85
• C. 98
• D. 80

Hint:

Convert mole fraction to moles, then calculate masses, finally use mass percent formula.

Answer 1

The Correct Option is C

Mole fraction $x_\text{H2SO4}=0.9$. Let 1 mole solution → 0.9 mol H$_2$SO$_4$, 0.1 mol H$_2$O. Mass H$_2$SO$_4$ = $0.9\times 98 = 88.2$ g, mass H$_2$O = $0.1 \times 18 = 1.8$ g. Mass % = $88.2/90 \times 100 \approx 98%$.