Question

How many moles of ethylene glycol must be added to 1 kg of water to make a solution with a freezing point of -2.4°C? The freezing point depression constant for water is 1.86°C•kg/mol. What is the molality of the solution?

Answer 1

1) C (m=T f/Kf)

2) 2.4 C

3) 1.3 m

4) 1.3 moles

Step-by-step explanation:

This is correct on ed

Answer 2

Answer: 1.29 moles of ethylene glycol must be added to 1 kg of water to make a solution with a freezing point of -2.4°C. Molality of solution is 1.29 m.

Step-by-step explanation:

Depression in freezing point is given by:

`\Delta T_f=i* K_f* m`

`\Delta T_f=T_f^0-T_f=(0-(-2.4))^0C=2.4^0C` = Depression in freezing point

i= vant hoff factor (for non electrolyte , i = 1)

`K_f` = freezing point constant for water=
`1.86^0C/kgmol`

m= molality =
`\frac{\text{moles of solute}}{\text{weight of solvent in kg}}`

m= molality =
`(x)/(1kg)`

`2.4^0C=1* 1.86^0C/kgmol* (x)/(1kg)`

`x=1.29`

Molality =
`\frac{\text{moles of solute}}{\text {weight of solvent in kg}}=(1.29mol)/(1kg)=1.29m`

Thus 1.29 moles of ethylene glycol must be added to 1 kg of water to make a solution with a freezing point of -2.4°C. Molality of solution is 1.29 m.