FP_depression - FREEZING POINT DEPRESSION DISCUSSION The...

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FREEZING POINT DEPRESSION DISCUSSION The vapor pressure of a solution containing a non-volatile solute is lower than that of the pure solvent. Consequently, the boiling point of a solution is higher. The freezing point of a solvent is also affected by the solute; the freezing point of a solution is lower than that of the pure solvent. The freezing point depression , Δ T f , is defined as Δ T f = freezing point of solvent – freezing point of solution The freezing point depression , like the boiling point elevation , is termed a colligative property . Such properties depend only on the concentration of the solute particles, and not on their nature. For dilute solutions, Δ T f = mK f where m = molality (moles of soute particles per kg of solvent) K f = molal freezing point depression constant, a property of the solvent. For solutions of electrolytes, such as NaCl, the solute ionizes in solution. Thus there are more solute particles than for the same number of moles of a non- electrolyte. For NaCl, Na + (aq) and Cl - (aq) exist in solution. As a result, the molality of the solute particles (ions in this case) is twice that for a non-
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This note was uploaded on 12/09/2011 for the course SP 108 taught by Professor Whittenburg during the Summer '11 term at Montgomery College.

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FP_depression - FREEZING POINT DEPRESSION DISCUSSION The...

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