a solution containing 10.0 g of an unknown solute and 90 g water has a freezing

Question

a solution containing 10.0 g of an unknown solute and 90 g water has a freezing point of -3.33 degrees. kf = 1.86degrees C/m for water. find molar mass of unknown solute a solution containing 10.0 g of an unknown solute and 90 g water has a freezing point of -3.33 degrees. kf = 1.86degrees C/m for water. find molar mass of unknown solute a solution containing 10.0 g of an unknown solute and 90 g water has a freezing point of -3.33 degrees. kf = 1.86degrees C/m for water. find molar mass of unknown solute

Explanation / Answer

We know that T f = iKf x m
Where

T f = depression in freezing point

        = freezing point of pure solvent – freezing point of solution

        = 0 -(-3.33) oC

        = 3.33 oC

K f = depression in freezing constant of water = 1.86oC/m

i = vanthoff’s factor = 1

m = molality of the solution

    = ( mass / Molar mass ) / weight of the solvent in Kg

    = ( 10.0 / M ) / 0.090

    = 111.1 / M

Plug the values we get

3.33 = 1x1.86x(111.1/M)

So M = 62.1 g/mol

Therefore the molar mass of the unknown solute is 62.1 g/mol

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