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JAMB Chemistry 2019 Paper

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Question : 45

Total: 80

A compound contains 40.0% carbon, 6.7% hydrogen and 53.3% oxygen. If the molar mass of the compound is 180. Find the molecular formula.

[H = 1, C = 12, O = 16]

C $_3$ H $_6$ O $_3$
C $_6$ H $_6$ O $_3$
C $_6$ H $_{12}$ O $_6$
CH $_2$ O

Solution:

C → 40/12 ≈ 3

H → 6.7/1 ≈ 6

O → 53.3/16 ≈ 3

dividing through with the lowest value, 3

C $_1$ H $_2$ O $_1$

[C $_1$ H $_2$ O $_1$ ]n = 180

[12 + 2 + 16]m = 180

30n = 180

n = 6

:C $_6$ H $_12$ O $_6$

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