Download Writing and Predicting Chemical Reactions


_________________________________
Reaction Types
Metathesis
Double
Displacement
Neutralization
Redox
Precipitation
Ion Exchange
Ions are combined to form new compounds
Synthesis
Decomposition
Single
Displacement
Combustion
Electron Transfer
Electrons are lost from one atom, or group of atoms, and gained by
another atom, or group of atoms, resulting in new atomic interactions
forming new compounds
Statement of AP Equations
Reactions presented in this reference are unbalanced molecular and net ionic equations. If only one equation is
shown, the molecular and net ionic equations are identical. We commonly use molecular equations, full ionic equations and
net ionic equations in class and lab to compare the amounts of reactants and products. This reference is not intended to
focus on stoichiometric relationships but is intended to help you begin to understand patterns in chemical reactivity. Below
are the directions for writing net ionic equations as you will be writing them in the equation section on the AP Exam. Even
though you will be writing equations in this form in the Chemical Equations section on all of my unit exams from now on as
well as on the national AP exam, you should recognize the importance of writing balanced molecular and balanced net ionic
equations for quantitative chemistry.
For each of the following three reactions, in part (i) write a balanced equation for the reaction and in part (ii) answer the question
about the reaction. In part (i), coefficients should be in terms of lowest whole numbers. Assume that solutions are aqueous unless
otherwise indicated. Represent substance in solutions as ions if the substances are extensively ionized. Omit formulas for any ions or
molecules that are unchanged by the reaction. You may use any empty space for scratch work, but only the equations and answers that are
written in the spaces provided will be graded.
Example:
A strip of magnesium metal is added to a solution of sliver (I) nitrate.
(i) Balanced Equation:
(ii) Which substance is oxidized in the reaction?
Metathesis Reactions
(AX + BY → AY +BX)
Formally known only as double displacement
These problems involve mixing two solutions. Each solution is a water solution of an ionic compound or ionized
molecule such as an acid or base. From the mixture of the two solutions, at least one insoluble precipitate, molecular solid,
molecular liquid or molecular gas will form. Any ions present as reactants and products are soluble and called spectator
ions; they are not included in the net ionic equation. You must know your solubility rules to do these problems.
I. Precipitation Reactions
AX(aq) + BY(aq) → AY(?) + BX(?)
1. A solution of silver nitrate is added to a solution of hydrochloric acid:
Molecular AgNO3 + HCl → AgCl + HNO3
Net Ionic ►Ag+ + Cl- → AgCl
(All chlorides are soluble except those containing silver, lead, and mercury.)
2. Barium nitrate is added to a solution of potassium chromate:
Ba(NO3)2 + K2CrO4 → BaCrO4 + KNO3
►Ba2+ + CrO42- → BaCrO4 (Most chromates will be insoluble except those of most group I and group II metals)
3. Lead chlorate is added to a solution of ammonium carbonate:
Pb(ClO3)2 + (NH4)2CO3 → PbCO3 + NH4ClO3
►Pb2+ + CO32- → PbCO3 (All carbonates are insoluble except group I metals)
4. Iron(III) nitrate is added to a strong sodium hydroxide solution:
Fe(NO3)3 + NaOH → Fe(OH)3 + NaNO3
►Fe3+ + OH- → Fe(OH)3 (Most hydroxides are insoluble except those of group I metals and ammonium)
5. Strontium chloride is added to a solution of sodium sulfate:
SrCl2 + Na2SO4 → SrSO4 + NaCl
►Sr2+ + SO42- → SrSO4
(All sulfates are soluble except those containing strontium, barium, calcium, lead,
and silver)
mercury
II. Acid / Base Neutralization
Acid + Base → Salt + Water
*These reactions only apply to strong acid/strong base combinations. For other acid/base reactions, see sec tion below.
1. Hydrochloric acid is added to potassium hydroxide:
Molecular HCl + KOH → H2O + KCl
Net Ionic ►H+ + OH- → H2O
2. Hot nitric acid is added to solid sodium hydroxide:
HNO3 + NaOH → NaNO3 + H2O
►H+ + OH- → H2O
3. Equal volumes of 0.5 M Sulfuric acid and 0.5 M sodium hydroxide are mixed:
H2SO4 + NaOH → NaHSO4 + H2O
►H2SO4 + OH- → HSO4- + H2O
Or
NaHSO4 + NaOH → Na2SO4 + H2O
►H+ + OH- → H2O
III. Double Displacement
Metallic Oxide + Acid → Salt + H2O
1. Ferric oxide is added to hydrochloric acid:
Molecular Fe2O3 + HCl → FeCl3 + H2O
Net Ionic ►Fe2O3 + H+ → Fe3+ + H2O
2. Copper(II) oxide is added to nitric acid:
CuO + HNO3 → Cu(NO3)2 + H2O
►CuO + H+ → Cu2+ + H2O
Nonmetallic Oxide + Base → Salt + H2O
1. Carbon dioxide gas is bubbled through a solution of sodium hydroxide:
Molecular CO2 + NaOH → Na2CO3 + H2O
Net Ionic ►CO2 + OH- → CO32- + H2O
2. Sulfur dioxide gas is bubbled through a solution of lithium hydroxide:
SO2 + LiOH → LiSO2 + H2O
►SO2 + OH- → SO32- + H2O
Acid + Non-hydroxide base → Salt + Molecular gas
1. Hydrochloric acid is added to aqueous sodium sulfide:
Molecular HCl + Na2S → NaCl + H2S
Net Ionic
►H+ + S2- → H2S
2. Solid sodium bicarbonate is added to hydrochloric acid:
H2CO3 → H2O + CO2
Redox Reactions
These problems involve the combination of two or more reactants in which there is a change in the oxidation state of
one or more atoms as the reactants are converted to products. Any species that exist as ions on both sides of the reaction are
omitted from the reaction. Be careful not to omit a non ion from the equation. Activity Series and Reduction Potential
Series can be used to make predictions about oxidation state changes. In this packet, the unbalanced half reactions are listed
before the net ionic equation.
IV. Synthesis Reactions A.K.A. Combination
A + B → AB
Reactions of Alkali Metals and Alkaline Earth Metals
Metal + Nonmetal → Salt* (Metal Ion+ + Nonmetal Ion-)
Group IA
Metal (M)
All
All
Li
Li
Na
K, Rb, Cs
+
Combining
Substance
→
Hydrogen & Halogen
Sulfur
Nitrogen
Oxygen
Oxygen
Oxygen
Group IIA
Metal (M)
+
All
Ca, Sr, Ba
Mg, Ca, Sr, Ba
Mg, Ca, Sr, Ba
Be, Mg, Ca, Sr, Ba
Combining
Substance
Halogens
Hydrogen
Nitrogen
Sulfur
Oxygen
→
Reaction
2 M(s) + X2(g) –> 2 MX(s)
2 M(s) + S(g) –> M2S(s)
6 Li(s) + N2(g) –> 2 Li3N(s)
4 Li(s) + O2(g) –> 2 Li2O(s)
2 Na(s) + O2(g) –> Na2O2(s)
M(s) + O2(g) –> M O2(s)
Reaction
M(s) + X2 –> MX2(s)
M(s) + H2(g) –> MH2(s)
3 M(s) + N2(g) –> M3N2(s)
M(s) + S(s) –> MS(s)
2 M(s) + O2(g) –> 2MO(s)
M = symbol for the metal, X = any halogen
1. Boron trichloride gas and ammonia gas are mixed:
BCl3 + NH3 → BCl3NH3
 If this compound is not familiar, try drawing a Lewis diagram to see how it is put together.
 This reaction is also an example of a Lewis Acid/Base reaction.
2. Calcium metal is heated in the presence of nitrogen gas:
Ca + N2 → Ca2N2
3. Solid Potassium is added to a flask of oxygen gas:
K + O2 → KO2
 This reaction is also true for rubidium and cesium. (Note: These are superoxides.)
4. A piece of solid magnesium is added to water:
Half Reactions o: Mg → Mg2+
r: H2O → H2
Net Ionic
►Mg + H2O → MgO + H2
V. Decomposition
AB → A + B
1. A sample of calcium carbonate is heated:
Half Reactions o: Ca2+ → CaO
r: CO32- → CO2
Net Ionic
CaCO3 → CaO + CO2
2. Hydrogen peroxide is gently warmed:
o: H2O2 → O2
r: H2O2 → H2O
H2O2 → H2O + O2
3. Manganese dioxide (acting as a catalyst) is added to a solid sample of potassium chlorate and the
mixture is then heated:
MnO2
KClO3 → KCl + O2
4. Solid aluminum hydroxide is heated:
Al(OH)3 →Al2O3 + H2O
VI. Single Displacement
A + BC → AC + B
Metal Displacement
Metal + Metal ion → Metal + Metal ion
1. A strip of zinc metal is added to a solution of copper(II) nitrate:
Molecular
Zn + CuNO3 → ZnNO3 → Cu
Half Reactions o: Zn → Zn2+
r: Cu2+ → Cu
Net Ionic
►Zn + Cu2+ → Zn2+ + Cu (notice this is a single replacement rxn)
2. A piece of aluminum is dropped into a solution of lead chloride:
Al + PbCl2 → Pb + AlCl3
o: Al → Al3+
r: Pb2+ → Pb
►Al + Pb2+ → Pb + Al3+
Some Common Departures
3. A piece of sodium metal is added to water:
2M(s) + 2H2O → 2M+(aq) + 2OH-(aq) + H2(g) (common pattern for all Group I)
Molecular 2 Na(s) + 2 H2O → 2 NaOH(aq) + H2(g)
Half Reactions
o: Na → Na+
r: H2O → H2
Net Ionic ►2 Na(s) + 2 H2O → 2 Na+(aq) + 2 OH-(aq) + H2(g)
4. A piece of calcium is added to a beaker of distilled water.
M(s) + H2O → M2+(aq) + 2OH-(aq) + H2(g) (common pattern for all Group II except Mg)
Ca(s) + 2H2O → Ca(OH)2(aq) + H2(g)
o: Ca → Ca2+
r: H2O → H2
►Ca(s) + 2H2O → Ca2+(aq) + 2OH-(aq) + H2(g)
5. A piece of magnesium is added to a beaker of water.
Mg(s) + H2O → MgO(s) + H2(g) (special, single replacement)
o: Mg → MgO
r: H2O → H2
►Mg(s) + H2O → MgO(s) + H2(g)
Halogen Displacement
Halogen + Halogen ion → Halogen + Halogen ion
1. Chlorine gas is bubbled through a solution of sodium iodide:
Molecular
Cl2 + NaI → NaCl + I
Half Reactions o: I-→ I2
r: Cl2 → ClNet Ionic
►Cl2 + I- → I2 + Cl2. Chlorine gas is bubbled through a strong solution of potassium bromide:
Cl2 + KBr → KCl + Br2
o: Br- → Br2
r: Cl2 → Cl►Cl2 + Br- → Cl- + Br2
3. Bromine gas is bubbled through a solution of sodium fluoride
Br2 + NaF → NaBr + F2
o: F- → F2
r: Br2 → Br(Or other halide.)
► Br2 + F- → Br- + F2
Hydrogen Displacement
Acid + Metal → Salt + Hydrogen
1. Sulfuric acid is added to a solid strip of zinc:
Molecular
Half Reactions
Net Ionic
H2SO4 + Zn → ZnSO4 + H2
o: H- → H2
r: Zn →Zn2+
► H+ + Zn → H2 + Zn2+
2. A piece of magnesium is dropped into a beaker of 6 M hydrochloric acid:
Mg + HCl → MgCl + H2
o: H- → H2
r: Mg → Mg2► Mg + H+ → Mg2+ + H2
3. Calcium metal is added to a solution of 4 M HCl:
Ca + HCl → CaCl + H2
o: Ca → Ca2+
r: H- → H2
► Ca + H+ → Ca2+ + H2
4. Strontium turnings are added to a 4M sulfuric acid solution:
Sr + H2SO4 → SrSO4 + H2
o: Sr→ Sr2+
r: H+ → H2
► Sr + H+ + SO42- → SrSO4 + H2
5. Silver is added to a solution of hydrochloric acid:
Ag + HCl → AgCl + H2
o: Ag → Ag+
r: H- → H2
►Ag + H+ + Cl- → AgCl + H2
Some Common Departures
6. Lead shot is dropped into hot, concentrated sulfuric acid:
Molecular
Pb + H2SO4 → PbSO4 + SO2 + H2O
Half Reactions
o: Pb → Pb2+
r: SO42- → SO2
Net Ionic
►Pb + H+ + SO42- → PbSO4 + SO2 + H2O
Note the departure from the general guideline.
7. Solid copper shavings are added to a concentrated nitric acid solution. (This reaction is well known and is covered quite
extensively in textbooks, note how it departs from the guidelines.)
o: Cu → Cu2+
r: NO3- → NO2
►Cu + H+ + NO3- → Cu2+ + H2O + NO2
w/ Dilute nitric acid
o: Cu → Cu2+
r: NO3- → NO
►Cu + H+ + NO3- → Cu2+ + H2O + NO
VII. Combustion
Substance + Oxygen Gas → Oxide of Element
The usual products are the oxides of the elements present in the original substance in their higher valence states. When N, Cl, Br, and I are
present in the original compound, they are usually released as free elements, not as the oxides.
1. Solid copper(II) sulfide is heated strongly in oxygen gas*:
CuS + O2 → CuO + SO2
or
→ Cu2O + SO2
2. Carbon disulfide gas is burned in excess oxygen gas*:
CS2 + O2 → CO2 + SO2
3. Methanol is burned completely in air*:
CH3OH + O2 → CO2 + H2O
 All alcohols, hydrocarbons and carbohydrates burn in oxygen gas to produce CO2 and H2O.
4. Silicate is combusted in a stream of oxygen gas*:
SiO4 + O2 → SiO2 + H2O
5. Hydrogen gas is mixed with oxygen gas and the mixture is sparked:
H2 + O2 → H2O
o: H2 → H2O
r: O2 → H2O
► H2 + O2 → H2O
*Half reactions cannot be written for combustion of ionic solids
(Common Oxidation State Changes for Oxidizing and Reducing Agents)
1. NO2- → NO3-
10. Na2O2 → NaOH
2. HNO3 → NO2
(concentrated)
11. H2O2 → H2O + O2
3. HNO3 → NO
(dilute)
12. HClO4 → Cl-
4. Sn2+ → Sn4+
13. Cl2 –dilute basic sol’n→ ClO-
5. MnO4- → Mn2+
(in acid solution)
14. Cl2 –conc. basic sol’n→ ClO2-
6. MnO2 → Mn2+
(in acid solution)
15. Cr2O72- → Cr3+
7. MnO4- → MnO2
(in neutral or basic solution)
16. S2O32- → SO2
8. H2SO4 → SO2
(hot, concentrated)
17. NH3 → NH4+
9. SO32- or SO2(aq) → SO42-
(In acid)
18. C2O4 → CO2
Exceptions (Non-Redox)
VIII. Oxide Reactions
Metallic Oxide + H2O → Base (Metallic Hydroxide)
Synthesis
1. Lithium oxide is added to water:
Molecular Li2O + H2O → LiOH
Net Ionic ►Li2O + H2O → Li+ + OH2. A solid piece of potassium oxide is dropped into cold water:
K2O + H2O → KOH
►K2O + H2O → K+ + OH-
Nonmetallic Oxide + H2O → Acid
1. Dinitrogen pentoxide is added to water:
Molecular N2O5 + H2O → HNO3
Net Ionic ►N2O5 + H2O → H+ + NO32. Carbon Dioxide gas is bubbled through water:
CO2 + H2O → H2CO3 (Carbonic acid)
or
→ H+ + HCO3- (weak acid)
Synthesis
3. Sulfur trioxide gas is bubbled through water:
SO3 + H2O → H2SO4
►SO3 + H2O → H+ + SO424. Phosphorus(V) oxytrichloride is added to water:
POCl3 + H2O → H3PO4 + H+ + Clor
→ H+ + H2PO4- + Clor
→ H+ + HPO42- + Cl-
One Exception
5. Nitrogen dioxide added to water
NO2 + H2O → HNO3 + NO
NO2 → NO + NO3H2O → H+
►NO2 + H2O → H+ + NO3- + NO (Is Redox)
Metallic Oxide + Nonmetallic Oxide → Salt
1. Solid calcium oxide is added to silicon dioxide and the mixture is heated strongly:
CaO + SiO2 → CaSiO3
2. Magnesium oxide is heated strongly in carbon dioxide gas:
MgO + CO2 → MgCO3
3. Calcium oxide is heated in an environment of sulfur trioxide gas:
CaO + SO3 → CaSO4
Organic Reactions
X. Substitution
Halogenation of an Alkane
1. Chlorine gas is added to a flask of methane gas and heated:
CH4 +Cl2 → CH3Cl + HCL
or
→ CH2Cl2 + HCL
or
→ CHCl3 + HCL
or
→ CCl4 + HCL
Synthesis
Preparation of an Amine
2. Chloromethane is bubbled through a solution of warm ammonia:
CH3Cl + NH3 → CH3NH2 + HCl
or
→ [CH3NH3]+Clor
→ [CH3NH3]+ + Cl-
XI. Organic Addition
Hydration of an Alkene
1. Hot steam is mixed with propene gas:
C3H6 + H2O → C3H7OH
Halogenation of an Alkene
2. Ethene gas is heated in the presence of chlorine gas:
C2H4 + Cl2 → C2H4Cl2
XII. Organic Elimination
Dehydration of an Alcohol
1. Ethanol is heated in the presence of sulfuric acid:
H2SO4
C2H5OH → C2H4 + H2O
Dehyrdohalogenation of a Haloalkane
2. Chloroethane is heated:
C2H5Cl → C2H4 + HCL
XIII. Organic Condensation
Esterification of an Alcohol
1. Methanol is mixed with acetic acid and then gently warmed:
esterification
CH3OH + CH3COOH --------> CH3COOCH3 + H2O
Dehydration Synthesis of an Alcohol
2. Methyl alcohol is mixed with a small amount of sulfuric acid and then warmed gently:
CH3OH + HOCH3 →CH3OCH3 +H2O
Saponification of an Ester
3. Methyl benzoate is mixed with sodium hydroxide and then gently warmed.
C6H5 COOCH3 + NaOH → C6H5 COO- + CH3OH
The remaining reactions will not be seen until third trimester.
More Acid/Base Reactions
Base + Amphoteric Metal → Salt + Hydrogen Gas
Amphoteric metals (such as Al, Zn, Pb, and Hg) have properties that may be intermediate between those of metals
and those of nonmetals. They will react with a base to form a complex ion with oxygen. This is a rare problem.
1. A piece of solid aluminum is added to a 6 M solution of sodium hydroxide:
Molecular Al + NaOH → Na3AlO3 + H2
o: Al → AlO33r: OH- → H2
Net Ionic ►Al + OH- → AlO33- + H2
2. A solid piece of zinc is added to a 6 M solution of potassium hydroxide:
Zn + KOH → K2ZnO2 + H2
o: Zn→ ZnO22r: OH- → H2
►Zn + OH- → ZnO22- + H2
Strong Acid + Salt of Weak Acid → Salt of Strong Acid + Weak Acid
1. Hydrochloric acid is added to potassium acetate:
Molecular HCl + KAc → HAc + KCl
Net Ionic ►H+ + Ac- → HAc
(Do not dissociate a weak acid.)
2. A 9 M nitric acid solution is added to a solution of potassium carbonate:
HNO3 + K2CO3 → H2CO3 + KNO3
►H+ + CO32- → H2CO3
Weak Acid + Weak Base → Conjugate Base + Conjugate Acid
1. A solution of ammonia is mixed with an equimolar solution of hydrofluoric acid:
NH3 + HF → NH4+ + F2. Acetic acid is added to a solution of ammonia:
HC2H3O2 + NH3 → C2H3O2- + NH4+
Weak Acid + Strong Base → Water + Conjugate Base
1. Hydrofluoric acid is added to a solution of sodium hydroxide:
Molecular HF + NaOH → NaF + H2O
Net Ionic ►HF + OH- → H2O + F2. A solution of vinegar (acetic acid) is titrated with lye (sodium hydroxide):
HC2H3O2 + NaOH → NaC2H3O2
►HC2H3O2 + OH- → H2O + C2H3O23. Nitrous acid is added to sodium hydroxide:
HNO2 + NaOH → NaNO2 + H2O
►HNO2 + OH- → H2O + NO2-
Strong Acid + Weak Base → Conjugate Acid (Weak Acid)
1. Hydrochloric acid is added to a solution of ammonia:
Molecular HCl + NH3 → NH4+ + ClNet Ionic ►H+ + NH3 → NH4+
2. Sulfuric acid is added to a solution of sodium fluoride:
H2SO4 + NaF → Na2SO4 + HF
►H+ + F- → HF
3. Hydrochloric acid is added to sodium carbonate:
HCl+ Na2CO3 → NaCl + HCO3►H+ + CO32- → HCO3Or
HCl+ Na2CO3 → NaCl + H2CO3
►H+ + CO32- → H2CO3
Or
HCl+ Na2CO3 → NaCl + CO2 + H2O
►H+ + CO32- → CO2 + H2O
4. Sodium acetate is added to a weak solution of nitric acid:
NaC2H3O2 + HNO3 → NaNO3 + HC2H3O2
►C2H3O2- + H+ → HC2H3O2
IX. Complex Ions1
Lewis Acid/Base Reactions
1. A concentrated solution of ammonia is added to a solution of zinc nitrate:
Molecular Zn(NO3)2 + NH3 → Zn(NH3)42+ + NO3Net Ionic ►Zn2+ + NH3 → Zn(NH3)42+
or
2+
Zn + NH3 + H2O → Zn(OH)2 + NH4+
2. A solution of iron(III) iodide is added to a solution of ammonium thiocyanate:
Common Ligands:
H2O, NH3, CN-, OH-, Cl-,
SCN-, N-, Br-, CO32-, C2O42-,
C5H5N, SCN-
FeI3 + NH4SCN → Fe(SCN)63- + NH4+
►Fe3+ + SCN- → Fe(SCN)633. A solution of copper(II) nitrate is added to a strong solution of ammonia:
Cu(NO3)2 + NH3 → Cu(NH3)42+ + NO3►Cu2+ + NH3 → Cu(NH3)42+
4. A concentrated potassium hydroxide solution is added to solid aluminum hydroxide:
KOH + Al(OH)3 → Al(OH)4- + K+
►OH- + Al(OH)3 → Al(OH)4-
1
Ligands are generally electron pair donors (Lewis bases). Ligands bond to a central atom that is usually the positive ion of a transition metal, forming complex
ions and coordination compounds. On the AP exam, the number of ligands attached to a central metal ion is often twice the oxidation number of the central metal ion.