CHM 1046 Exam 2 Study Guide (Chapters 12/13/14/16) Questions With 100% Verified Answers

Colligative Properties - correct answers - Properties that depend on the concentration of solute particles but not on their identity. - Vapor pressure lowering, boiling point elevation, freezing point depression, and osmotic pressure. Colloid - correct answers A mixture of two or more substances mixed together that can be separated. ex. Milk (Protein and fat globules dispersed in liquid), Smoke (Solid soot particles dispersed in air), and Gelatin (water dispersed in a protein medium) Calculate the molality of a 17.5% (by mass) aqueous solution of nitric acid. - correct answers Equation: Molality = moles of solute / kg of solution 1.) Find Grams of Nitric Acid and Solution (Water). 17.5% - 17.5 g of Nitric Acid 100 g - 17.5 g = 82.5 g of Solution (Note: You don't convert 17.5% to 0.0175 because it's assumed that the solution is out of 100g) 2.) Calculate Moles of Solute Molar Mass of Nitric Acid: 63.01 g /mol 17.5g / 63.01 g*mol-1 = 0.2777 mol 3.) Calculate Molality Convert grams of solution to kilograms 82.5 g * 1 kg / 1000 g = 0.0825 kg Molality = moles of solute / kg of solution 0.2777 mol / 0.0825 kg = 3.3661 mol/kg Answer: 3.37 m A solution is prepared by dissolving 15.0 g of NH3 in 250.0g of water. The density of the resulting solution is 0.974 g/mL. The molarity of the NH3 in the solution is ___________. - correct answers 1.) Find mass of NH3 solution 15.0g + 250g = 265.0g 2.) Find volume of NH3 solution Volume = mass / density (g/mL) 265.0g / 0.974g*mL-1 = 272.074 mL 3.) Find moles of NH3 Molecular Weight of NH3 = 17.031g/mol 15.0g / 17.031 g*mol-1 = 0.881 mol 4.) Find Molarity (M) of NH3 Solution Convert milliliters to liters. Milliliters to Liters = 272.074 mL x 1 L / 1000mL = 0.2721 L Molarity = moles of solute / Liters of solution (mol/L) 0.881 mol / 0.2721 L = 3.238 M (mol/L) Answer: 3.24 M A solution is prepared by dissolving 15.0 g of NH3 in 250.0g of water. The density of the resulting solution is 0.974 g/mL. The molality of the NH3 in the solution is ___________. - correct answers 1.) Find mass of NH3 solution 15.0g + 250g = 265.0g 2.) Find moles of NH3 Molecular Weight of NH3 = 17.031g/mol 15.0g / 17.031 g*mol-1 = 0.881 mol 3.) Find Molality (m) of NH3 Solution Convert grams to kilograms. Grams to Kilograms = 265.0g x 1 kg/1000g = 0.265 kg Molality = moles of solute / kilograms of solution (mol/kg) 0.881 mol / 0.265 kg = 3.325 mol/kg Answer: 3.33 m Raoult's Law Equation - correct answers Equation: Psolution = Xsolvent * Psolvent Keywords in Question: Pure Substance, Vapor Pressure Units: (atm or torr) = (nA / nA + Nb) * (atm or torr) Psolution = Vapor pressure of the solution Xsolvent = Mole fraction of the solvent - (mol solvent / mol solvent + mol solute) Psolvent = Vapor Pressure of the pure solvent The vapor pressure of pure ethanol at 60°C is 0.459 atm. Raoult's Law predicts that a solution prepared by dissolving 10.00 mmol naphthalene (nonvolatile) in 90.0 mmol ethanol will have a vapor pressure of ________ atm. - correct answers Equation: Psolution = Xsolvent * Psolvent 1.) Plug into Raoult's Law Equation Psolution = Xsolvent * Psolvent Psolution = (90.0 mmol / 90.0 mmol + 10.00mmol) * (0.459atm) 2.) Find Mole Fraction Xsolvent = mol solvent / mol solvent + mol solute Xsolvent = 90.0 mmol / 90.0 mmol + 10.00 mmol Xsolvent = 0.9 (Note: No need to convert mmol to mol since all the units will cancel out) 3.) Solve for Psolution