Question

Which substance will most affect the freezing point of water if one mole of the substance is added to one kilogram of water?

PbS

C8H18

Na3PO4

NaCl

Answer 1

NaCl.because salt increases the boiling point of water

Answer 2

Answer:
`Na_3PO_4`

Step-by-step explanation:

Depression in freezing point is given by:

`\Delta T_f=i* K_f* m`

`\Delta T_f` = Depression in freezing point

i= vant hoff factor

`K_f` = freezing point constant

m= molality =
`\frac{moles}{\text {weight of solvent in kg}}=(1)/(1)=1m`

1. For
`PbS`

, i= 1 as it is a non electrolyte and does not dissociate.

2. For
`C_8H_(18)`

, i= 1 as it is a non electrolyte and does not dissociate.

3. For
`Na_3PO_4`

, i= 4 as it is a electrolyte and dissociate to give 4 ions.

`Na_3PO_4\rightarrow 3Na^(+)PO_4^(3-)`

4. For
`NaCl`

, i= 2 as it is a electrolyte and dissociate to give 2 ions.

`NaCl\rightarrow Na^(+)+Cl^(-)`

Thus as vant hoff factor is highest for
`Na_3PO_4` and the freezing point will be most affected.