Part B A solution of water ( K f=1.86 ?C/ m ) and glucose freezes at ? 2.75 ?C.

Question

Part B

A solution of water (Kf=1.86 ?C/m) and glucose freezes at ? 2.75 ?C. What is the molal concentration of glucose in this solution? Assume that the freezing point of pure water is 0.00 ?C.

Express your answer to three significant figures and include the appropriate units.

Part C

A solution of water (Kb=0.512 ?C/m) and glucose boils at 102.06 ?C. What is the molal concentration of glucose in this solution? Assume that the boiling point of pure water is 100.00 ?C.

Express your answer to three significant figures and include the appropriate units.

Explanation / Answer

B)

we know that

depression in freezing point is given by

dTf = i x Kf x m

as glucose is a non electrolyte

i=1

so

dTf = Kf x m

now

dTf = freezing point of pure water - freezing point of solution

given

freezing point of pure water is 0 C

so

dTf = 0 - (-2.75)

dTf = 2.75

also

given

Kf = 1.86

so using those values

we get

dTf = kf x m

2.75 = 1.86 x m

m = 1.48

so

the molal conc of glucose is 1.48m

C)

we know that

elevation in boiling point is given by

dTb = i x Kb x m

as glucose is a non electrolyte

i=1

so

dTb = Kb x m

now

dTb =boiling point of solution - boiling point of pure water

given

boiling point of pure water is 100 C

so

dTb = 102.06 - 100

dTb = 2.06

also

given

Kb = 0.512

so using those values

we get

dTb = kb x m

2.06 = 0.512 x m

m = 4.02

so

the molal conc of glucose is 4.02m

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