Q. 14 4.0( 3 Votes )

Give reasons for the following:

a. When 2g of benzoic acid is dissolved in 25 g of benzene, the experimentally determined molar mass is always greater than the true value.

b. A mixture of ethanol and acetone shows positive deviation from Raoult’s Law.

c. The preservation of fruits by adding a concentrated sugar solution protects against bacterial action.

Answer :

a. The experimentally determined molar mass is always greater than the true molar mass as it doesn’t account for the dimers formed during this reaction. In this reaction, benzoic acid forms dimers in benzene, therefore the no. of particles reduce which reduces the molar mass of the reaction mixture. Dimers are nothing but, two identical atoms held together.

b. A mixture of ethanol and acetone is a non - ideal solution. It does not obey Rault’s law.


According to Rault’s law,

For any solution the partial vapour pressure of each component is directly proportional to its mole fraction.

Its vapor pressure is high, and therefore it shows a positive deviation from the rault’s law. This deviation occurs due to the very low intermolecular forces of attraction between the solute - solvent molecules, and it is very easy for them to escape to a pure state.

c. This occurs due to osmosis. As we know sugar solution is a hypertonic solution(A hypertonic solution is a solution which has a higher concentration than the surrounding solution concentration). The water from the bacteria cells gets out, and the bacteria loses all its water shrivels and die.

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