Question

Pure water boils at 100ºC (212ºF). When a substance is added to the water the boiling point increases due to what is referred to as the boiling point elevation. (a) What is the molecular mass of sucrose (C₁₂H₂₂O₁₁)? (b) If you add 100 g of sucrose to water, how many moles of sucrose would you then have? (c) If you add the sucrose to 500 g of water, by what fraction would you divide? (Hint: boiling point elevation for water is 0.521ºC for each mole of solute dissolved in 1000 g of solvent) (d) What will the boiling point elevation be if 100 g of sucrose is added to 500 g of water? (boiling point elevation for water is 0.521ºC for each mole of solute dissolved in 1000 g of solvent) (e) What will the boiling point be if 100 g of sucrose is added to 500 g of water?

Answer 1

mols sucrose = grams sucrose/molar mass sucrose.

molality sucrose = mols sucrose/kg solvent.

delta T = Kb*molality

boiling point of soln = 100 + delta T.