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**CALCULATIONS INVOLVING COLLIGATIVE PROPERTIES**

Section 18.4

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**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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MOLALITY Molality (m) – the number of moles of solvent dissolved per kilogram of solvent m = mol solute / kg solvent Mole fraction nA = moles of solute A nB moles of solvent B XA = nA XB = nB nA + nB nA + nB

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**BOILING POINT ELEVATION**

Change in boiling point temperature ΔTb = Kb * m ΔTb = change in boiling pt temp Kb = molal boiling-point elevation constant Depends on the solvent Units (oC / m) m = molality (mole / kg)

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**FREEZING POINT DEPRESSION**

Change in freezing point temperature ΔTf = Kf * m ΔTf = change in freezing pt temp Kf = molal freezing-point depression constant Depends on the solvent Units (oC / m) m = molality (mole / kg)

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**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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Calculations Involving Colligative Properties. Objectives When you complete this presentation, you will be able to o calculate the molality of a solution.

Calculations Involving Colligative Properties. Objectives When you complete this presentation, you will be able to o calculate the molality of a solution.

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