C4H10 CsH12 CoHi4 C,H16 CBH18 propane butane pentane hexane heptane octane POST-

Question

C4H10 CsH12 CoHi4 C,H16 CBH18 propane butane pentane hexane heptane octane POST-LABORATORY QUESTIONS 1. Except for very small alkanes (hydrocarbons), the boiling point rises 20-30 degrees for each additional carbon atom in the molecule. Assume that the normal boiling point of the fuel in the lighter is 10°C, why was it not necessary to extend the table further (i.e., why was it unlikely that your unknown contained more than eight carbon atoms per molecule)? 2. A gaseous hydrocarbon collected over water at a temperature of 21°C and a barometric pressure of 753 torr occupied a volume of 48.1 mL. The hydrocarbon in this volume weighs 0.1133 g. Calculate the molecular mass of the hydrocarbon. 3. How is the ideal gas law related to the molar mass of a gas? Date Signature 131

Explanation / Answer

PV = nRT, P = pressure, V = Volume, R =Gas constant, T =Temperature, n = number of moles.

V= 48.1 mL = 0.0481 L, Pressure = 753 torr = 0.990789 atm , T = 21 oC = 294.15 K

weight of sample M = 0.1133 g, R = 0.08205 L atm / mol·K

n = PV /RT = (0.990789 atm x 0.0481 L)/(0.08205 L atm / mol·K x 294.15 K) = 0.0019746 mole

Mass of the gas = 0.1133 g

Mass of the gas/mole = 0.1133 g / 0.0019746 mole = 57.38 g/mol.

3. PV = nRT and n = m/M.W.

P = pressure, V = Volume, R =Gas constant, T =Temperature, n = number of moles, m = mass of the gas, M.W. = molecular weight of the gas.

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