Home
Class 12
CHEMISTRY
What mass of NaCI ("molar mass" =58.5g m...

What mass of `NaCI ("molar mass" =58.5g mol^(-1))` be dissolved in `65g` of water to tower the freezing point by `7.5^(@)C`? The freezing point depression constant, `K_(f)`, for water is `1.86 K kg mol^(-1)`. Assume van't Hoff factor for `NaCI` is `1.87`.

Text Solution

Verified by Experts

Calculation of molality (m) of solution
molality (m)=`(DeltaT_(f))/(ixxK_(f))`
`DeltaT_(f)=7.5^(@)C=7.5K,K_(f)=1.86 K kg mol^(-1), i=87`
`m=((7.5K))/((1.87)xx(1.86 K kg mol^(-1)))=2.156 mol K^(-1), i=1.87`
Calculation of mass of sodium chloeide (solute)
`m=("Mass of solute in grams/molar mass")/("Mass of solvent in kg")`
m=2.156 `mol^(-1) kg^(-1)`,Molar mass=58.5 g `mol^(-1)`, Mass of solvent=65g=0.0065 kg
`(2.156 mol kg^(-1)), =W/((58.5 g mol^(-1))xx(0.065 kg))`
`W=(2.156 mol kg^(-1))xx(58.5 g mol^(-1))xx(0.065 kg)`=8.2 g
Promotional Banner

Similar Questions

Explore conceptually related problems

What mass of ethlene ethyelne glycol ("molar mass"=62 g mol^(-1)) must be dissolved in 5.5kg of water to lower the freezing point of from 0^(@)C to-10^(@)C ? (K_(f)) for water=1.86 K kg mol^(-1) ).

What mass of ethylene glycol (molar mass = "62.0 g mol"^(-1) ) must be added to 5.50 kg of water to lower the freezing point of water from 0^(@)C to -10.0^(@)C ( k_(f) for water = "1.86 K kg mol"^(-1) ).

A solution of sucrose (molar mass = 342 g mol^(-1)) has been prepared by dissolving 68.5g of sucrose in 1000g of water. The freezing point of the solution obtained will be: (K_(f) for water = 1.86 K kg mol^(-1))

A solution of sucrose (molar mass =342 g mol^(-1) ) has been prepared by dissolving 68.5 g of sucrose in 1000 g of water. The freezing point of the solution obtained will be ( K_(f) for water = 1.86K kg mol^(-1) )

Calculate the amount of CaCI_(2) ("molar mass"=111 g mol^(-1)) which must be added to 500 g of water to lower its freezing point by 2 K assuming CaCI_(2) to be completely dissoviated (K_(f) for = 1.86 "K kg mol"^(-1)) .