84 STEP 4. Review the Knowledge You Need to Score High
Free-Response Questions
First Free-Response Question
You have 10 minutes. You may not use a calculator.Answer all three of the following questions. Each question will have two parts—writing the
balanced chemical equation and answering a question about the reaction. Coefficients in
the balanced chemical equation must be in the lowest whole-number ratio. Do not include
formulas for substances that remain unchanged during the reaction. Unless otherwise
noted, assume all the reactions occur in aqueous solution. If a substance is extensively
ionized and therefore is present as ions in solution, write its formula as ions.
Example: Hydrochloric acid is added to a lead(II) nitrate solution.a. Excess sodium hydroxide is added to an aluminum sulfate solution.
Which species behaves as a Lewis acid in the reaction? Explain.b. An acidified iron(II) sulfate solution is added to a potassium permanganate solution.
Describe the color change occurring as the reaction proceeds.c. Dichlorine heptaoxide is mixed with water.
What is the oxidation number of the chlorine in the product?Second Free-Response Question
You have 10 minutes. You may not use a calculator.Answer all three of the following questions. Each question will have two parts—writing the
balanced chemical equation and answering a question about the reaction. Coefficients in
the balanced chemical equation must be in the lowest whole-number ratio. Do not include
formulas for substances that remain unchanged during the reaction. Unless otherwise
noted, assume all the reactions occur in aqueous solution. If a substance is extensively
ionized and therefore is present as ions in solution, write its formula as ions.
Example: Hydrochloric acid is added to a lead(II) nitrate solution.Pb^2 ++2 Cl−→PbCl 2a. Metallic strontium is added to warm water.
If phenolphthalein indicator was added to the resulting solution, what would be the
color of the solution? Explain.b. Solid manganese(IV) oxide is added to concentrated hydrochloric acid.
What is the oxidation number of the species being oxidized before and
after the reaction takes place?c. A lead(II) nitrate solution is mixed with an ammonium sulfate solution.
Which ions, if any, are spectator ions in this reaction?Pb^2 +−+→ 2 Cl PbCl 2