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Concentration Units Molarity (M) (mol solute)/(L of solution) % by mass (g solute/g of solution) x 100 % Molality (m) (mol solute)/kg of solvent) mole fraction (X) (mol solute)/(total moles) 1. Calculate the percentage by mass of the solute in a solution of 5.50g of NaBr in 78.2 g of solution 2. Calculate the amount of water that must be added to 5.00g of urea (NH2)2CO to make a 16.2 percent by mass solution 3. Calculate the molality of a solution that contains 14.3 g of sucrose (C12H22O11) in 676 g of water. 4. Calculate the molality of a 1.22 M sucrose solution. The density of the solution is 1.12 g/mL. 5. What is the mole fraction of sugar in a 1.22 M solution of sucrose? (1.12g/mL) 6. The density of a solution containing 10.0 % ethanol (C2H5OH) by mass is 0.984 g/mL. What volume of this solution would contain 0.125 mol of ethanol? Colligative Properties PA=PA°XA Tb=Kbm =MRT P=PA°XB Tf=Kfm 7. The vapor pressure of a glucose(C6H12O6) solution is 17.01 torr at 20°C while that of pure water is 17.25 torr at the same T. What is the molality of the solution? 8. Ethylene glycol, CH2(OH)CH2(OH), is a common automolbile antifreeze. It is water soluble and faorly nonvolatile (b.p=197°). Calculate the freezing point of a solution containing 651 g of EG in 2505g of water. Would you keep this solution in your car in the summer? (Kb and Kf for water are 0.52°C/m and 1.86°C/m respectively.) 9. The average osmotic pressure of seawater is about 30.0 atm at 25°C. calculate the molar concentration of an aqueous solution of urea that is isotonic with seawater. 10. A 0.86 percent by mass solution of NaCl is called “physiological saline” because its osmotic pressure is equal to that of the solution in red blood cells. Calculate the osmotic pressure of this solution at normal body Temperature (37°C). The density of the saline solution is 1.005 g/mL. 11. A forensic chemist is given a white powder for analysis. She dissolves 0.50 g of the substance in 8.0 g of benzene (C6H6). The solution freezes at 3.9°C. Can she conclude that the substance is probably cocaine (C17H21NO4) ?(Pure benzene freezes at 5.5° C and Kf for benzene is 5.12°C/m).
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