Question

Calculate the amount of depression that will occur when 5 g of sodium chloride is dissolved into 0.250 kg of water. Remember when sodium chloride dissolves in water it breaks into two particles. The kf for water is 0.512 0C/m.

Answer 1

Answer : The amount of depression will be,
`0.35^oC`

Explanation : Given,

Mass of sodium chloride = 5 g

Mass of water = 0.250 kg

Molar mass of sodium chloride = 58.5 g/mole

Formula used :

`\Delta T_f=i* K_f* m\\\\\Delta T_f=i* K_f*\frac{\text{Mass of sodium chloride}}{\text{Molar mass of sodium chloride}* \text{Mass of water in kg}}`

where,

`\Delta T_f` = change in freezing point

i = Van't Hoff factor for electrolyte solution (sodium chloride) = 2

`K_f` = freezing point constant =
`0.512^oC/m`

m = molality

Now put all the given values in this formula, we get

`\Delta T_f=2* 0.512^oC/m* (5g)/(58.5g/mol* 0.250Kg)`

`\Delta T_f=0.35^oC`

Therefore, the amount of depression will be,
`0.35^oC`