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Reactions and Periodicity: Free-Response Questions for AP Chemistry

By — McGraw-Hill Professional
Updated on Feb 1, 2011

Review the following concepts if necessary:

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.
    Pb2+ + 2Cl → PbCl2
  1. Excess sodium hydroxide is added to an aluminum sulfate solution.
  2. Which species behaves as a Lewis acid in the reaction? Explain.

  3. An acidified iron(II) sulfate solution is added to a potassium permanganate solution.
  4. Describe the color change occurring as the reaction proceeds.

  5. Dichlorine heptaoxide is mixed with water.
  6. 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.
    Pb2+ + 2Cl → PbCl2
  1. Metallic strontium is added to warm water.
  2. If phenolphthalein indicator was added to the resulting solution, what would be the color of the solution? Explain.

  3. Solid manganese(IV) oxide is added to concentrated hydrochloric acid.
  4. What is the oxidation number of the species being oxidized before and after the reaction takes place?

  5. A lead(II) nitrate solution is mixed with an ammonium sulfate solution.
  6. Which ions, if any, are spectator ions in this reaction?

Answers and Explanations

First Free-Response Question

  1. 4 OH + Al3+ → Al(OH)4
  2. The aluminum ion behaves as the Lewis acid, because it is accepting electron pairs from the hydroxide anion.

    You get 1 point for the correct formulas for the reactants and products and 1 point for the correct coefficients in the balanced equation. Answering the associated question correctly is worth 1 point.

  3. 5 Fe2+ + 8 H+ + MnO4 → 5 Fe3+ + Mn2+ + 4 H2O
  4. The purple color of the permanganate ion slowly disappears as the reaction proceeds.

    You get 1 point for the correct formulas for the reactants and products and 1 point for the correct coefficients in the balanced equation. Answering the associated question correctly is worth 1 point.

  5. Cl2O7 + H2O → 2 H+ + 2 ClO4
  6. The oxidation number of the chlorine in the perchlorate ion is +7.

    You get 1 point for the correct formulas for the reactants and products and 1 point for the correct coefficients in the balanced equation. Answering the associated question correctly is worth 1 point.

    There is a maximum of 9 points possible.

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