Question #22370

The analysis of a hydrocarbon revealed that it was 85.6281% C and 14.3719% H by mass. When1.8gofthegaswasstoredina1L flask at 93.4515◦C, it exerted a pressure of 489 Torr. What is the molecular formula of the hydrocarbon?

Expert's answer

Firstwe find the molar mass of the the gas

pV = m/M R T;

65 190*0.001 = 1.8 / M * 8.314 * 366.4515

M = 1.8 * 8.314 * 366.4515 / 65 190 * 0.001;

M = 84 g/mol

Then find the mass and amount of substances of each element

n = m/M

m(C) = 1.8 * 0.856281 = 1.54g; n (C) = 1.54 / 12 = 0.128 g/mol

m(H) = 1.8 * 0.143719 = 0.259g; n (H) = 0.259 / 1 = 0.259 g/mol

The amount of substances are correlated as:

n(H) : n(C) = 0.259 : 0.128 or 2 : 1

Knowing the the molar mass can construct a mathematical equation and to solve

it

12x + 1 * 2x= 84

14x = 84;

x = 84/14

x = 6

so the formula will be C_{6}H_{12}

pV = m/M R T;

65 190*0.001 = 1.8 / M * 8.314 * 366.4515

M = 1.8 * 8.314 * 366.4515 / 65 190 * 0.001;

M = 84 g/mol

Then find the mass and amount of substances of each element

n = m/M

m(C) = 1.8 * 0.856281 = 1.54g; n (C) = 1.54 / 12 = 0.128 g/mol

m(H) = 1.8 * 0.143719 = 0.259g; n (H) = 0.259 / 1 = 0.259 g/mol

The amount of substances are correlated as:

n(H) : n(C) = 0.259 : 0.128 or 2 : 1

Knowing the the molar mass can construct a mathematical equation and to solve

it

12x + 1 * 2x= 84

14x = 84;

x = 84/14

x = 6

so the formula will be C

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## Comments

Rae24.01.13, 00:37Thank you. This was very helpful.

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