Sample 1Medium
A compound contains 40.0% carbon, 6.67% hydrogen and 53.3% oxygen by mass, and its molar mass is 180 g mol^-1. What is its molecular formula? (C = 12, H = 1, O = 16)
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The answer is B.
Moles per 100 g: C = 40.0/12 = 3.33, H = 6.67/1 = 6.67, O = 53.3/16 = 3.33, a ratio of 1 : 2 : 1, so the empirical formula is CH2O (30 g mol^-1). n = 180/30 = 6, so the molecular formula is C6H12O6.
- A.
CH2O is the empirical formula; its mass is 30 g mol^-1, not 180.
- C.
C3H6O3 has a molar mass of 90 g mol^-1, not 180.
- D.
C2H4O2 has a molar mass of 60 g mol^-1, not 180.
NCERT: Class 11 Chemistry, Chapter 1, 1.9