CHM Exam 3 Study Guide

A saturated solution Correct Answers contains the maximum amount of solute that will dissolve in that solvent at that temperature. Heat of solution Correct Answers may be positive, zero, or negative, depending on the relative strength of the solute-solvent, solute-solute, and solvent-solvent attractive forces. In which of the following solvents would you expect KBr to be most soluble? Correct Answers CH3CH2OH (ethanol) -- because it is polar like KBr Which of the following compounds should be soluble in CCl4? Correct Answers C8H18 -- because it is nonpolar like CCl4 How many grams of water are needed to dissolve 27.8 g of ammonium nitrate NH4NO3 in order to prepare a 0.452 m solution? Correct Answers 0.452 m = 0.452 moles/kg 27.8 g NH4NO3 = 27.8/80.05 = 0.3473 moles 0.452 = 0.3473/x where x = kg water x = 0.3473/0.452 = 0.768 kg = 768 g In how many grams of water should 25.31 g of potassium nitrate (KNO3) be dissolved to prepare a 0.1982 m solution? Correct Answers 0.1982 m = 0.1982 moles/kg 25.31 g KNO3 = 25.31/101.1 = 0.2503 moles 0.1982 = 0.2503/x where x = kg water x = 0.2503/0.1982 = 1.263 kg = 1,263 g Calculate the molality of a solution containing 14.3 g of NaCl in 42.2 g of water. Correct Answers Molality = moles/kg = (14.3/58.45)/0.0422 = 5.80 m What is the molality of a solution that is 3.68 % by mass calcium chloride? Correct Answers 3.68 % = 3.68g CaCl2/100 g solution = 3.68 g CaCl2/(100 - 3.68) g water Molality = moles/kg = (3.68/111)/0.0963 = 0.344 m What is the mass percent CH3OH of a 0.256 m CH3OH(aq) solution? Correct Answers 0.256 m CH3OH = 0.256 x 32.04 g CH3OH/kg water = 8.202g/1,000 g Mass percent = (8.202/1,008.202) x 100 = 0.814 % Consider a solution made from a nonvolatile solute and a volatile solvent. Which statement is true? Correct Answers The boiling point of the solution is always greater than the boiling point of the pure solvent. Dissolving a solute such as KOH in a solvent such as water results in Correct Answers a decrease in the vapor pressure of the liquid.