194 Step 4. Review the Knowledge You Need to Score High
Free-Response Questions
First Free-Response Question
You have 20 minutes to answer the following questions. You may not use a calculator. You
may use the tables at the back of the book.Five beakers each containing 100.0 mL of an aqueous solution are placed on a lab
bench. The solutions are all at 25°C. Solution 1 contains 0.20 M KNO 3. Solution 2 con-
tains 0.10 M BaCl 2. Solution 3 contains 0.15 M C 2 H 4 (OH) 2. Solution 4 contains 0.20 M
(NH 4 ) 2 SO 4. Solution 5 contains 0.25 M KMnO 4.a. One of the solutions could oxidize two of the other solutions. Which solution is it?
Which solutions could it oxidize?
b. Which solution has the lowest pH? Explain.
c. Which pair of solutions would give a precipitate if they are mixed? What is the formula
for this precipitate?
d. Which solution would be the poorest conductor of electricity? Explain.
e. Rank the solutions in order of increasing boiling point. Explain.Second Free-Response Question
You have 20 minutes to answer the following questions. You may not use a calculator. You
may use the tables in the back of the book.Five beakers are placed in a row on a countertop. Each beaker is half filled with a
0.20 M aqueous solution. The solutes, in order, are: (1) potassium sulfate, (2) methyl alco-
hol, (3) sodium carbonate, (4) ammonium chromate, and (5) barium chloride. The solu-
tions are all at 25°C.Answer the following questions with respect to the five solutions listed above.a. Which solution will form a precipitate when ammonium chromate is added to it?
Give the formula of the precipitate.
b. Which solution is the most basic? Explain.
c. Which solution will exhibit the lowest boiling-point elevation? Explain.
d. Which solution is colored?
e. Which of the other solutions will not react with solution (5), barium chloride?Answers and Explanations
First Free-Response Question
a. 1 point for picking solution 5, and 1 point for picking solutions 2 and 3.
b. 1 point for picking solution 4, and 1 point for saying the ammonium ion (NH 4 +) is a
weak acid, or that it undergoes hydrolysis.
c. 1 point for picking solutions 2 and 4, and 1 point for BaSO 4.
d. 1 point for picking solution 3, and 1 point for saying it is a non-electrolyte or that it
does not ionize.
e. 1 point for the order: 3 < 2 < 1 < 5 < 4, and 1 point for the explanation. The explanation
must relate the order to the number (concentration) of solute particles in the solution.There is a total of 10 points possible.