Copyright 1988, 1990 by College Board
AP Free Response – 1988

4) Use appropriate ionic and molecular formulas to show the reactants and the products for the following, each of which occurs in aqueous solution except as indicated. Omit formulas for any ionic or molecular species that remain unchanged after the reaction. You need not balance. In all cases a reaction occurs.

(b) A solution of sodium hydroxide is added to a solution of ammonium chloride.
(c) A strip of magnesium is added to a solution of silver nitrate.
(d) Solid potassium chlorate is heated in the presence of manganese dioxide as a catalyst.
(e) Dilute hydrochloric acid is added to a solution of potassium carbonate.
(f) Sulfur trioxide gas is added to excess water.
(g) Dilute sulfuric acid is added to a solution of barium chloride.

AP Free Response – 1990

4) Give the formulas to show the reactants and the products for FIVE of the following chemical reactions. Each of the reactions occurs in aqueous solution unless otherwise indicated. Represent substances in solution as ions if the substance is extensively ionized. Omit formulas for any ions or molecules that are unchanged by the reaction. In all cases a reaction occurs. You need not balance.

Example: A strip of magnesium is added to a solution of silver nitrate.
Mg + Ag+ ---> Mg2+ + Ag

(a) Solutions of sodium iodide and lead nitrate are mixed.
(b) A solution of ammonia is added to a solution of ferric chloride.
(d) Solutions of silver nitrate and sodium chromate are mixed.
(e) Hydrogen sulfide gas is bubbled through a solution of potassium hydroxide.
(g) A piece of solid bismuth is heated
(h) A strip of copper metal is added to a concentrated solution of sulfuric acid.

1988 Answers
4) Average score = 5.66
3 points for each reaction; 1 pt. for reactants and 2 for products. Two points (of the three) for correct response in inappropriate form, i.e. molecular when ionic is correct. One point penalty for spurious product, e.g. redox product in an acid-base reaction. One point penalty for inclusion of spectator ions.

b) OH¯ + NH4+ ---> H2O + NH3 (or NH4OH)
c) Mg + Ag+ ---> Mg2+ + Ag
d) KClO3 ---> KCl + O2
(MnO2 is also shown over the reaction arrow in the original.)
e) H+ + CO32¯ ---> CO2 + H2O (or H2CO3 or HCO3¯)
f) SO3 + H2O ---> H+ + HSO4¯ (or H+ + SO42¯)
g) Ba2+ + SO42¯ ---> BaSO4
(or Ba2+ + HSO4¯ ---> BaSO4 + H+)

1990 Answers
4) 
a)* Pb2+ + 2I¯ -----> PbI2
b) Fe3+ + NH3 + H2O ----> Fe(OH)3 + NH4+ (NH4OH is OK in place of NH3 + H2O)
Fe2+ + others above-----> Fe(OH)2 + NH4+ (given two points)
d)* Ag+ + CrO42¯ -----> Ag2CrO4
e) H2S + OH¯ -----> S2¯ (or HS¯) + H2O
g) Bi + O2 -----> Bi2O3 (Bi2O5 = one point)
h) Cu + H+ + HSO4¯ (or SO42¯) -----> Cu2+ + SO2 + H2O (any two products is given one point; all three must be there for 3 points; omitting H+ and/or H2O is minus one point)
(*Correct equation but wrong charge on ion(s) = one point)