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Colligative Properties Physical properties that are affected by the concentration of solute.

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Presentation on theme: "Colligative Properties Physical properties that are affected by the concentration of solute."— Presentation transcript:

1 Colligative Properties Physical properties that are affected by the concentration of solute.

2 Colligative Properties Most common examples are freezing point, boiling point, and vapor pressure.

3 Colligative Properties Freezing point – decreased Boiling point – increased Vapor pressure - decreased

4 Colligative Properties This makes sense based on kinetic theory. It is harder to freeze with a weird shape in the way. It is harder to boil or have a vapor pressure, because these properties are due to movement of molecules and it is harder to get moving with a weird shape in the way.

5 Colligative Properties For freezing point and boiling point changes, we will use one of two formulas :

6 Colligative Properties MW = (grams of solute)(k) (kg of solvent) ( T) MW = molecular weight T = change in boiling or freezing point K = a constant that varies depending on the solvent.

7 Colligative Properties MW = (grams of solute)(k) (kg of solvent) ( T) For water: K f = 1.86 (freezing) K b =.51 (boiling)

8 Colligative Properties This formula can also be arranged as follows: K b = K f T b T f T b = change in boiling temperature T f = change in freezing temperature

9 Colligative Properties The other formula that can be used is T = m (k) (n) T = change in freezing or boiling m = molality of the solution k = freezing or boiling constant n = the number of ions the substance dissociates into when dissolved in water


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