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*For all equations D represents delta or "the change in" which is normally represented witha triangle

Colligative Properties- is characteristic of the solvent and depends on the concentration but not the nature of the solute.(boiling point elevation and freezing point dpression are both colligative properties.

Freezing Point- The temperature at which a solid turns to a liquid.

Freezing point depression- occurs when a solute is dissolved in a solvent.  The freezing point of the solution will be lower than that of the original pure solute.

The amount that the freezing point is lowered depends on two factors.

1.The concentration of the solute. The more solute the more the freezing point will be lowered.  Thus  a 2 molal solution of sugar and water will have a lower boiling point than a 1 molal solution of water and sugar.

2.The nature of the Solvent. Two solution of the same concentration of solute will freeze at different temperatures if they are composed of different solvents.

The relationship between lowering of freezing point and the molal concentration of a solution can be expressed as

DTf=Kfm

DT= depression of freezing point

K= molal freezing point constant

m= molal concentration of the solution

What is the freezing point of a solution of 15.0 g of NaCl in 250 g of water? The molal freezing point constant, Kf, for water is 1.86 oC kg / mol.

DTf=Kfm

For Na Cl, i = 2. The concentration of the solution is 1.03 m in NaCl. 
Therefore, the change in the freezing point of the water is -3.8 oC. 
The freezing point of the solution is, therefore, -3.8 oC.

Boiling Point Elevation- A solution boils at a higher than that of the pure solvent.

http://img.sparknotes.com/chemistry/solutions/colligative/gifs/dtekbm.gif

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