Net Ionic Reactions – Practice #3
1. (i) Gaseous hydrogen chloride is dissolved in water
HCl + H2O --> H3O+ + Cl- [Arrhenius version also accepted]
(ii) Why is the molecular compound hydrogen chloride able to dissolve in
water? HCl is very polar as is water and thus the two molecules are attracted to
one another
2. (i) A solution containing tin(II) ions is added to acidified potassium dichromate
solution.
3 Sn2+ + 14 H+ + Cr2O72- --> 3 Sn4+ + 2 Cr3+ + 7 H2O
(ii) There is a color change during this reaction; which atom is most likely
responsible? Explain --the chromium changes in oxidation state and is a
transition metal; most transition metal compounds are colored and the color
changes with oxidation state
3. (i) Magnesium turnings are added to a solution of iron(III) chloride
3 Mg + 2 Fe3+ --> 3 Mg2+ + 2 Fe (or Fe2+: Mg + 2 Fe3+  Mg2+ + 2 Fe2+)
(ii) Describe a color change that corresponds to the reaction you write
the chromium changes in oxidation state and is a transition metal; most
transition metal compounds are colored and the color changes with oxidation
state
4. (i) Solid aluminum sulfide is added to water
Al2S3 + 6 H2O --> 2 Al(OH)3 + 3 H2S
(ii) Describe the odor expected for the final reaction mixture the H2S should give
the solution the odor of rotten eggs
5. (i) Hydrogen gas is passed over hot iron(III) oxide
3 H2 + Fe2O3 -->2 Fe + 3 H2O
(ii) Which substance is reduced? the iron in the Fe2O3 is reduced to Fe
6. (i) Solid potassium chlorate is heated in the presence of a manganese(IV) oxide
catalyst.
2 KClO3 --> 2 KCl + 3 O2
(ii) What is the oxidation number of chlorine before and after the reaction? the
chlorine starts as +5 and ends as -1
7. (i) Acetic acid is burned in an excess of oxygen.
CH3COOH + 2 O2 --> 2 CO2 + 2 H2O
(ii) How many molecules of products are formed from the burning of 1 molecule
of acetic acid? 4 molecules (2 of each product)
8. (i) Hydrogen chloride gas is oxidized by oxygen gas.
4HCl (g) + O2 --> 2Cl2 + 2H2O
(ii) If three moles of hydrogen chloride gas and three moles of oxygen gas react
as possible, which reactant, if any, is present in excess? Justify your answer. O2
would be in excess because of the stoichiometry of the reaction; 4 moles of HCl
are consumed for 1 mole of O2. (It takes only 0.75 mole of O2 to react with 3
moles of HCl, leaving an excess of 2.25 moles of O2.) – check this math before
posting it
Note – The rest of these do not have a part (ii) question, but will on the AP Exam.
9. (i) Powdered iron is added to a solution of iron(III) sulfate.
Fe + Fe2(SO4)3 
10. (i) Solid barium carbonate is added to excess acetic acid.
BaCO3 + HC2H3O2  Ba(C2H3O2)2 + H2CO3
BaCO3 + HC2H3O2  Ba+2 + 2(C2H3O2)- + H2O + CO2
11. (i) Solutions of lead nitrate and magnesium sulfate are mixed.
Pb(NO3)2 + MgSO4 -> PbSO4 + Mg(NO3)2
Pb+2 + SO4-2  PbSO4