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# CALCULATIONS INVOLVING COLLIGATIVE PROPERTIES

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CALCULATIONS INVOLVING COLLIGATIVE PROPERTIES
Section 18.4

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

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

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)

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)

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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