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CALCULATIONS INVOLVING COLLIGATIVE PROPERTIES Section 18.4.

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Presentation on theme: "CALCULATIONS INVOLVING COLLIGATIVE PROPERTIES Section 18.4."— Presentation transcript:

1 CALCULATIONS INVOLVING COLLIGATIVE PROPERTIES Section 18.4

2 AFTER READING SECTION 18.4, YOU SHOULD KNOW: How to calculate molality (m) How to calculate the molar mass of a molecular compound from the freezing point depression or boiling point elevation

3 MOLALITY Molality (m) – the number of moles of solvent dissolved per kilogram of solvent m = mol solute / kg solvent Mole fraction n A = moles of solute An B moles of solvent B X A = n A X B = n B n A + n B n A + n B

4 BOILING POINT ELEVATION Change in boiling point temperature ΔT b = K b * m ΔT b = change in boiling pt temp K b = molal boiling-point elevation constant Depends on the solvent Units ( o C / m) m = molality (mole / kg)

5 FREEZING POINT DEPRESSION Change in freezing point temperature ΔT f = K f * m ΔT f = change in freezing pt temp K f = molal freezing-point depression constant Depends on the solvent Units ( o C / m) m = molality (mole / kg)

6 AFTER READING SECTION 18.4, YOU SHOULD KNOW: How to calculate molality (m) How to calculate the molar mass of a molecular compound from the freezing point depression or boiling point elevation


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