Derive the formula for a polyhydric alcohol whose vapor density in air is 2.138.

| March 19, 2021 | education

Derive the formula for a polyhydric alcohol whose vapor density in air is 2.138. The mass fractions of carbon, hydrogen, and oxygen are 38.7%, 9.7%, 51.6%, respectively.

Let the formula of alcohol CxHyOz

Let the mass of alcohol be 100 grams, then:

m (C) = 38.7 g

Let’s find the amount of carbon:

n (C) = m (C) / M (C) = 38.7 g / 12 g / mol = 3.225 mol

m (H) = 9.7 g

Let’s find the amount of hydrogen:

n (H) = m (H) / M (H) = 9.7 g / 1 g / mol = 9.7 mol

m (O) = 51.6 g

Let’s find the amount of oxygen:

n (O) = m (O) / M (O) = 51.6 g / 16 g / mol = 3.225 mol

Let’s establish the ratio of atoms:

x: y: z = n (C): n (H): n (O) = 3.225: 9.7: 3.225 = 1: 3: 1

Simplest formula: CH3O

M (CxHyOz) = D (air) * M (air) = 2.138 * 29 g / mol = 62 g / mol

M (CxHyOz) / M (CH3O) = 62 g / mol / 31 g / mol = 2, which means the molecular formula:

C2H6O2

Answer: C2H6O2



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