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Topic: Molar Mass Determination by Depression of the Freezing Point  (Read 3855 times)

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Offline ElectricRubberDucky

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1. An aqueous solution of sucrose was prepared by dissolving 34.58 g of C12H22O11 (M.M. = 342.34) in 100.0 mL of distilled water.
a.   How many moles of sucrose were dissolved in water?
b.   What is the solvent used to prepare the solution?
c.   What is the mass (kg) of the solvent?
d.   Calculate the molality of the sucrose solution.

2. The freezing point of the solution prepared in number 1 was found to be -1.9◦C.
a.   If the freezing point of pure water is 0.0◦C, what is the freezing depression for this solution?
b.   Using the freezing point depression constant, Kf, for water as 1.86◦C/molal and the molaloty of the solution calculated in number 1 letter d, what is the van’t Hoff factor, i, for sucrose?
c.   Based on the observed value of the van’t Hoff factor, i,for sucrose, what does this tell us about the number particles produced when sucrose is dissolved in water compared to the number of particles when sucrose is in the pure state?
d.   Is sucrose an electrolyte or nonelectrolyte?

Offline sjb

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Re: Molar Mass Determination by Depression of the Freezing Point
« Reply #1 on: July 26, 2008, 11:24:38 AM »
1. An aqueous solution of sucrose was prepared by dissolving 34.58 g of C12H22O11 (M.M. = 342.34) in 100.0 mL of distilled water.
a.   How many moles of sucrose were dissolved in water?
b.   What is the solvent used to prepare the solution?
c.   What is the mass (kg) of the solvent?
d.   Calculate the molality of the sucrose solution.

a. If you have mass, and molecular weight, can you calculate number of moles?

b. What is the definition of solvent?

c. How much of it do you have?

d. What is the definition of molality?

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