Akcl solution is prepared by dissolving 40.0 g kcl (molar mass = 74.55 g/mol) in 250.0 g of water (molar mass = 18.01 g/mol) at 25°c. what is the vapor pressure of the solution if the vapor pressure of water at 25°c is 23.76 mm hg?
a) 20.5 mm hg
b) 22.1 mm hg
c) 22.9 mm hg
d) 24.7 mm hg

Option (B) is the correct answer.

Explanation:

The given data is as follows.

    mass of KCl = 40 g,           mass of water = 250.0 g

Hence, number of moles of KCl will be calculated as follows.

             No. of moles =

                                  =

                                  = 0.537 mol

Number of moles of water will be calculated as follows.

            No. of moles =  

                                 =

                                 = 13.9 mol

Also, mole fraction of KCl will be calculated as follows.

                              =

                              =

                              = 0.037

Hence, calculate the vapor pressure of the solution as follows.

Here, i = 2 because KCl on dissociation produces 2 ions that is, and .

                  = 22.1 mm Hg

Thus, we can conclude that the vapor pressure of the given solution is 22.1 mm Hg.

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.