5 Steps to a 5 AP Chemistry

 Answers and Explanations

First Free-Response Question

a. 4 OH−+Al^3 +→Al(OH) 4 −

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.

b. 5 Fe^2 ++8 H++MnO 4 −→5 Fe^3 ++Mn^2 ++4 H 2 O

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.

c. Cl 2 O 7 +H 2 O →2 H++2 ClO 4 −

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.

Second Free-Response Question

a. Sr +2 H 2 O →Sr^2 ++2 OH−+H 2

The resulting solution is basic owing to the presence of the hydroxide ion. The

phenolphthalein indicator is pink in basic solutions, so the solution would be pink.

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.

b. MnO 2 +4 H++2 Cl−→Mn^2 ++Cl 2 +2 H 2 O

Chlorine is being oxidized from −1 in the chloride ion to 0 in diatomic chlorine gas.

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.

c. Pb^2 ++SO 42 −→PbSO 4

The spectator ions are the nitrate ions (NO 3 −) and the ammonium ions (NH 4 +).

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.

Reactions and Periodicity  85