# Derive the molecular formula of a carbohydrate-aldohexose, in which the mass fraction of carbon is 40%

Derive the molecular formula of a carbohydrate-aldohexose, in which the mass fraction of carbon is 40%, hydrogen-6.7%, oxygen-53.3%. Make the structural formulas of three isomers (in Fisher’s projections) that meet the condition of the problem.

Given:
ω (C) = 40%
ω (H) = 6.7%
ω (O) = 53.3%

Find:
CxHyOz -?

1) Let m (CxHyOz) = 100 g;
2) m (C) = ω (C) * m (CxHyOz) / 100% = 40% * 100/100% = 40 g;
3) n (C) = m (C) / M (C) = 40/12 = 3.33 mol;
4) m (H) = ω (H) * m (CxHyOz) / 100% = 6.7 * 100/100% = 6.7 g;
5) n (H) = m (H) / M (H) = 6.7 / 1 = 6.7 mol;
6) m (O) = ω (O) * m (CxHyOz) / 100% = 53.3% * 100/100% = 53.3 g;
7) n (O) = m (O) / M (O) = 53.3 / 16 = 3.33 mol;
8) x: y: z = 3.33: 6.7: 3.33 = 1: 2: 1;
9) CH2O – the simplest formula;
10) (CH2O) 6 – C6H12O6 – the true formula of the carbohydrate-aldohexose;
Answer: Unknown substance – C6H12O6.

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