Question

Which of the following would have the highest vapor pressure?








A.

1.0 M solution of ionic compound sodium chloride (NaCl)

B.

1.0 M solution of ionic compound potassium chloride (KCl)

C.

1.0 M solution of molecular compound sucrose (C12H22O11)

D.

pure water

Answer 1

In the vapour pressure of solution when the solute is mixed in water it will less than the actual solvent so the correct answer is pure water as it is universal solvent therefore water can disolve so many sustances in it 

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Answer 2

Answer : The correct options is, (D) Pure water.

Explanation :

According to the relative lowering of vapor pressure, the vapor pressure of a component at a given temperature is equal to the mole fraction of that component of the solution multiplied by the vapor pressure of that component in the pure state.

Formula used :

$\frac{\Delta p}{p^o}=i\times X_B$

where,

$p^o$ = vapor pressure of the pure component (water)

$p_s$ = vapor pressure of the solution  

$X_B$ = mole fraction of solute

i = Van't Hoff factor

(A) The dissociation of 0.1 M $NaCl$ will be,

$NaCl\rightarrow Na^++Cl^-$

So, Van't Hoff factor = Number of solute particles = $Na^++Cl^-$ = 1 + 1 = 2

(B) The dissociation of 0.1 M $KCl$ will be,

$KCl\rightarrow K^++Cl^-$

So, Van't Hoff factor = Number of solute particles = $K^++Cl^-$ = 1 + 1 = 2

(C) $C_{12}H_{22}O_{11}$, sucrose is a non-electrolyte solute that means they retain their molecularity, and not undergo association or dissociation.

So, Van't Hoff factor = 1

(D) Pure water : As we know that the vapor pressure of a pure solvent is always greater than the vapor pressure of a solution that containing a non-volatile liquid.

As we know that the vapor pressure is depend on the Van't Hoff factor but the vapor pressure of a pure solvent is always greater.

Hence, from this we conclude that, the pure water have the highest vapor pressure.