Question

The vapor pressure of 1 M of KI solution is ________ 1 M of glucose solution. This is because vapor pressure depends only on the _________.

Which option correctly completes this statement?
a) the same as; concentration of the solute
b) less than; number of particles of solute
c) less than; molar mass of the solute
d) higher than; molar mass of the solute

Answer 1

Answer: b) less than; number of particles of solute

Step-by-step explanation:

As the relative lowering of vapor pressure is directly proportional to the amount of dissolved solute.

The formula for relative lowering of vapor pressure will be,

`(p^o-p_s)/(p^o)=i* x_2`

where,

`(p^o-p_s)/(p^o)`= relative lowering in vapor pressure

i = Van'T Hoff factor

`x_2` = mole fraction of solute =
`\frac{\text {moles of solute}}{\text {total moles}}`

a) 1 M KI

i= 2 as it is a electrolyte and dissociates to give two ions.

`KI\rightarrow K^++I^-`

b) 1 M glucose

i= 1 as it is a non electrolyte and does not dissociate to give ions.

Thus as number of particles in 1 M KI is higher, the lowering in vapor pressure will be more.