The formula and the molecular weight of an unknown hydrocarbon compound are to b
ID: 845663 • Letter: T
Question
The formula and the molecular weight of an unknown hydrocarbon compound are to be determined by elemental analysis and the freezing-point depression method.
(a) A 5.000 g sample of the hydrocarbon is combusted and 17.142 g CO2 and 2.925 g H2O are produced. Calculate the empirical formula of the unknown hydrocarbon
(b) A solution is prepared by dissolving 2.53 grams of p-dichlorobenzene (molecular weight 147.0) in 25.86 grams of naphthalene (molecular weight 128.2). Calculate the molality of the p-dichlorobenzene solution.
(c) The freezing point of pure naphthalene is determined to be 80.2
Explanation / Answer
b) A solution is prepared by dissolving 2.53 grams of p-dichlorobenzene (molecular weight 147.0) in 25.86 grams of naphthalene (molecular weight 128.2). Calculate the molality of the p-dichlorobenzene solution.
m= moll solute/ 1.kg solvent = 2.53 x 1mol /147 / 0.02586 =0.666 mol
(c) The freezing point of pure naphthalene is determined to be 80.2
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