question_answer 75)

  Two beakers of capacity 500 mL were taken. One of these beakers, labelled as "A", was filled with 400 mL water whereas the beaker labelled "B' was filled with 400 mL of 2M solution of NaCL At the same temperature both the beakers were placed in closed containers of same material and same capacity as shown in figure. At a given temperature, which of the following statement is correct about the vapour pressure of pure water and that of NaCI solution? (a) Vapour pressure in container (A) is more than that in container (B) (b) Vapour pressure in container (A} is less than that in container (B) (c) Vapour pressure is equal in both the containers (d) Vapour pressure in container (B) is twice the vapour pressure in container (A)

Answer:

                  (a) When salt is added to water to make the solution the vapour pressure of solution get decreases. This is due to decrease in surface covered by solvent molecule which lead to decrease in number of solvent molecule escaping from the surface corresponding to pure solvent.                                            Hence, vapour pressure also get reduces.