Bronx University Process Exothermic or Endothermic Discussion

Overview

1. Indicate the principal type of solute–solvent interaction in each of the following solutions, and rank the solutions from weakest to strongest solute–solvent interaction:
   1. KCl in water,
   2. CH2Cl2 in benzene (C6H6),
   3. methanol (CH3OH) in water.
2. When ammonium chloride dissolves in water, the solution becomes colder.
   1. Is the solution process exothermic or endothermic?
   2. Why does the solution form?
3. The solubility of MnSO4 H2O in water at 20o C is 70 g per 100 mL of water.
   1. Is a 1.22 M solution of MnSO4 H2O in water at 20o C saturated, supersaturated, or unsaturated?
   2. Given a solution of MnSO4 H2O of unknown concentration, what experiment could you perform to determine whether the new solution is saturated, supersaturated, or unsaturated?
      
      
4. Assume that a portable reverse-osmosis apparatus operates on seawater, whose effective concentration (the concentration of dissolved ions) is 1.12 M, and that the desalinated water output has an effective molarity of about 0.02 M. What minimum pressure must be applied by hand pumping at 297 K to cause reverse osmosis to occur?
   
   
   
5. You make a solution of a nonvolatile solute with a liquid solvent. Indicate whether each of the following statements is true or false.
   1. The freezing point of the solution is higher than that of the pure solvent.
   2. The freezing point of the solution is lower than that of the pure solvent.
   3. The boiling point of the solution is higher than that of the pure solvent.
   4. The boiling point of the solution is lower than that of the pure solvent.
6. At 63.5o C, the vapor pressure of H2O is 175 torr, and that of ethanol (C2H5OH) is 400 torr. A solution is made by mixing equal masses of H2O and C2H5OH.
   1. What is the mole fraction of ethanol in the solution?
   2. Assuming ideal-solution behavior, what is the vapor pressure of the solution at 63.5oC?
   3. What is the mole fraction of ethanol in the vapor above the solution?
      
      
7. a. What boiling point would you predict for an aqueous sodium hydroxide solution that is 10 mole percent NaOH, assuming no ion pairing in solution?
   b. If the boiling point is measured to be 105.0o C, what is the true value of the van’t Hoff factor for this solution?

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