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Obtain the relationship between freezing point depression of a solution containing nonvolatile-nonelectrolyte solute and its molar mass. - Chemistry

Sum

Obtain the relationship between freezing point depression of a solution containing nonvolatile-nonelectrolyte solute and its molar mass.

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Solution

1. The freezing point depression (ΔTf) is directly proportional to the molality of solution.

Thus, ΔTf = Kf m         ….(1)

2. Suppose we prepare a solution by dissolving W2 g of solute in W1 g of solvent.

Moles of solute in W1 g of solvent = `"W"_2/"M"_2`

where, M2 is the molar mass of solute.

Mass of solvent = W1 g = `("W"_1 g)/(100 "g"//"kg") = "W"_1/1000` kg

3. The molality is expressed as,

m = `"Moles of solute"/"Mass of solvent in kg"`

m = `("W"_2//"M"_2  "mol")/("W"_1//1000 "kg")`

m = `(1000 "W"_2)/("M"_2 "W"_1) "mol kg"^-1`    ....(2)

4. Substituting equation (2) in equation (1), we get,

`triangle "T"_"f" = (1000 "K"_"f" "W"_2)/("M"_2 "W"_1)`

Hence,

`"M"_2 = (1000 "K"_"f" "W"_2)/(triangle "T"_"f" "W"_1)`

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APPEARS IN

Balbharati Chemistry 12th Standard HSC for Maharashtra State Board
Chapter 2 Solutions
Exercise | Q 6 | Page 46
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