Ethanol is commonly referred to simply as alcohol or spirits, It is the principa

Question

Ethanol is commonly referred to simply as alcohol or spirits, It is the principal type of alcohol found in alcoholic beverages. It is a psychoactive drug and one of the oldest recreational drugs used by humans. It can cause alcohol intoxication when consumed in sufficient quantity. It is a volatile, flammable, colorless liquid with the structural formula CH3CH2OH. The density of an aqueous solution containing 45 weight percent ethanol is 0.92472 g/mL.

a) A person weighing 75 kg takes a swallow of an alcoholic beverage corresponding to 25 gram of pure ethanol. It is assumed that the alcohol mixes evenly in person´s water phase, constituting 62 % of the person´s weight. Calculate the person´s ethanol mass per mille (alkoholpromille in Danish).

b) The vapor pressures of ethanol (C2H5OH) and 1-propanol (C3H7OH) at 35 oC are 100.0 mmHg and 37.6 mmHg, respectively. Assume ideal behaviour and calculate the partial pressures of ethanol and 1-propanol at 35 oC over a solution of ethanol in 1- propanol, in which the mole fraction of ethanol is 0.200.

Explanation / Answer

b) According to Raoult's law,

Partial pressure of A = Mole fraction of A x Vapor pressure of A in its pure form

Partial pressure of ethanol

Given that

vapor pressure of ethanol = 100 mmHg

mole fraction of ethanol = 0.200

Hence,

        partial pressure of ethanol = Mole fraction x vapor pressure in pure form

                                              = 0.200 x 100 mmHg

                                              = 20 mmHg

Therefore,

partial pressure of ethanol = 20 mmHg

Partial pressure of 1-propanol:

Given that

vapor pressure of 1- propanol = 37.6 mmHg

mole fraction of 1- propanol = 1 - mole fraction of ethanol = 1 - 0.2 = 0.8

Hence,

partial pressure of 1-propanol = Mole fraction x vapor pressure in pure form

                                          = 0.800 x 37.6 mmHg

                                          = 30.08 mmHg

Therefore,

partial pressure of 1-propanol = 30.08 mmHg

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