Question

Determination of Molar Mass by freezing Point depression

Not sure how to answer these two questions

Calcium chloride, CaCI_2 is commonly used as road salt. If one mole of CaCI_2 is dissolved in 1 kg v of water, would the freezing point of the solution be greater than, less than, or the same as a solution prepared by dissolving one mole of table sugar (sucrose, C_12H_22O_11) in 1 kg of water? Explain your answer. A student followed our lab procedure for this experiment. He started the experiment by measuring the mass and freezing point of the pure solvent with little error. Instead of quickly finishing the experiment, he went to lunch. After returning from lunch, he noted that the solvent had absorbed some impurities from the atmosphere. He went ahead and performed the experiment anyway. Determine whether the measured freezing point depression (Delta T) in the experiment would increase, decrease, or not change as compared to the value measured in an experiment where the solvent had no impurities in it (assume negligible change in the mass of the solvent after absorbing impurities). Also determine whether the measured molality of the solution (m) and the molar mass of the solute would increase, decrease, or not change.

Answer 1

Colligative properties:

The properties of solution which depends only on the concentration of solute particle are known as colligative properties. General meaning of colligative properties is “counting”, then we can say that the colligative properties of solution is depends on the counting particles of solutes.

Types of colligative properties:

There are four important colligavtive properties which are following:

1. Vapor pressure depression.

2. Boiling point elevation.

3. Freezing point depression.

4. Osmotic pressure.

All the above colligative properties follow the general relationship:

Colligative property = concentration or molality of solute * constant.

         

CaCl2 is a ionic salt it is ionizes into three ions thus the molality of the solution will be greater than the solution of suger solution. While sucrose is a covalent compound which was not ionize

Thus the freezing point of CaCl2 solution will be lower than the solution of 1 mole sucrose solution.