writing reaction equations for the a.p. chemistry exam
TRANSCRIPT
Writing Reaction Equations for the
A.P. Chemistry Exam
Common Chemicals List:
•NH3 – ammonia (window cleaner)
•HC2H3O2 – acetic acid or ethanoic acid (vinegar)
•C6H12O6 – glucose (blood sugar; simple sugar)
•C12H22O11 – sucrose (table sugar)
•C2H4(OH)2 – ethylene glycol (antifreeze)
•I2 in alcohol – tincture of iodine (alcohol solution of iodine found in small bottles in medicine cabinet)
•H2O2 – hydrogen peroxide (peroxide…3% solution found in brown bottles in medicine cabinet)
•NaClO – sodium hypochlorite (laundry bleach)
•O3 – triatomic oxygen (ozone)
Common Chemicals List:
•NaHCO3 – sodium bicarbonate (baking soda)
•Na2CO3 – sodium carbonate (washing soda)
•CH3OH – methanol (wood alcohol)
•C2H5OH – ethanol (grain alcohol)
•H3C6H5O6 – ascorbic acid (vitamin C)
•CaO – calcium oxide (lime)
•C10H8 – napthalene (moth balls…two fused benzene rings)
•C6H4Cl2 – paradichlorobenzene (also moth balls)
•SiO2 – silicon dioxide (amorphous-glass; crystalline- quartz; aka sand)
•C6H5CH3 – toluene, methylbenzene or phenylmethane (paint thinner, mineral spirits)
Three Letter Compounds:•TBA tertiary butyl alcohol•MEK methyl ethyl ketone•TTE trichloro trifluoro ethane•KHP potassium hydrogen phthalate
Putting together two solutions
1. PPT’s – Be familiar with the general solubility rules
2. Complex Ion Formation – Go over complexes formed in Qual. Labs.
Writing Reaction Equations for the A.P. Chemistry Exam
3. Bronsted-Lowrey Acid/Base - Be familiar with strong and weak acids and bases
Decompositions
3. Chlorates - When chlorates decompose they break down into metal chlorides and oxygen.
Writing Reaction Equations for the A.P. Chemistry Exam
1. Carbonates - When carbonates decompose they break down into metal oxides and carbon dioxide
5. Binary Compounds - Break down into their elements except for...6. Peroxides - Break down into the metal oxide and oxygen.
If you see what would be the products in a decomposition reaction as the reactants in a synthesis reaction, then view the reaction as a “reverse” decomposition
4. Hydroxides - When hydroxides decompose they break down into metal oxides and water.
2. Bicarbonates - When bicarbonates decompose they break down into metal carbonates, carbon dioxide water
Acidic or Basic Anhydrides in water1. Acidic - Covalently bonded oxides (nonmetals with oxygen) combine with water to make acids.
2. Basic - Ionically bonded oxides (metals with oxygen) combine with water to make bases.
Writing Reaction Equations for the A.P. Chemistry Exam
REDOX reactions1. MnO4
- and Cr2O72- are typically used as
oxidizers. (MnO4- typically is reduced
to Mn2+, Cr2O7
2- is typically reduced to Cr3+).2. Identify the half reactions…go through the steps of balancing to identify all species present (i.e. H+, OH-, H2O).
Writing Reaction Equations for the A.P. Chemistry Exam
3. Other substances to know about: CO (strong reducing agent); O2
2- (strong oxidizing agent); HNO3 and H2SO4 are oxidizing acids
Remember the reaction categories from the Honors Chem. course1. Synthesis - one product (look for reverse decompositions)
2. Single Replacement…remember activities
Writing Reaction Equations for the A.P. Chemistry Exam
3. Double Replacement
4. Combustion - hydrocarbon fuels react with oxygen to make carbon dioxide and water.
5. A Carbonate plus an Acid - always makes a salt, carbon dioxide and water
Make sure, after you are done, that you have considered:1. The major speciesmajor species present (i.e. weak acids should be shown as molecules whereas strong acids should be shown as ions).2. Only net ionic equationsnet ionic equations should be shown… don’t include spectator ions.
Writing Reaction Equations for the A.P. Chemistry Exam
3. Don’t worry about showing phases…you don’t need to show them. 4. Assume solutions are aqueous unless otherwise noted
5. Balance all equations w/ the smallest whole #’s
1.) Solutions of sodium iodide and lead nitrate are mixed.
Practice I
2NaI(aq) + Pb(NO3)2(aq) --> 2NaNO3(aq) + PbI2(s)
2I- + Pb2+ --> PbI2
PPT
2Na+ + 2I- + Pb2+ + 2NO3- --> 2Na+ + 2NO3
- + PbI2
The reverse reaction would likely be favored as raising the temperature generally increases the solubility of solids in liquids.
2.) A solution of hydrogen peroxide is heated.
2H2O2 --> 2H2O + O2
peroxide decomposition
The oxidation number of the oxygen in the reactants is -1; the oxidation number of the oxygen in the products is -2 and 0. This is a disproportionation reaction.
Practice I
3.) Hydrogen sulfide gas is bubbled through a solution of potassium hydroxide.
H2S + OH- --> H2O + HS-
B-L acid/base…also D.R. H2S(g) + KOH(aq) --> H2O(l) + KHS(aq)
H2S + K+ + OH- --> H2O + K+ +HS-
The color of the litmus would be blue. The product bisulfide, HS-, is a base stronger than water. Litmus is blue in the presence of a base.
Practice I
4.) Solid dinitrogen pentoxide is added to water
N2O5 + H2O -->2HNO3
acid anhydride
N2O5 + H2O --> 2H+ + 2NO3-
Less than 7. Dinitrogen pentoxide is an acid anhydride producing hydrogen ions in water decreasing the pH.
Practice I
5.) A piece of solid aluminum is heated strongly in oxygen.
4Al + 3O2 --> 2Al2O3
synthesis, redox
The aluminum would be the limiting reactant. One mole of aluminum would require 0.75 moles of oxygen. If equal numbers of moles of reactants were added, there would be extra oxygen.
Practice I
6.) A strip of copper metal is added to a concentrated solution of sulfuric acid
redox
Cu + 3H+ + HSO4- --> Cu2+ + 2H2O + SO2
The reddish brown copper metal would get used up and eventually go away. The solution would become more and more blue as the Cu2+ ion concentration increases.
Practice I
1.) Calcium oxide powder is added to distilled water.
CaO + H2O --> Ca(OH)2
basic anhydride
CaO + H2O --> Ca2+ + 2OH-
or
Practice II
This solution could be used to test for the gas carbon dioxide. The name of this solution is limewater
2.) Liquid bromine is shaken with a 0.5 M sodium iodide solution.
Br2(l) + 2NaI(aq) --> 2NaBr (aq) + I2(aq)
S.R. / redox
Br2 + 2I- --> 2Br- + I2
Br2 + 2Na+ +2 I- --> 2Na+ + 2Br- + I2
Practice II
The reducing agent in this reaction is the sodium iodide solution (or just the iodide ion). The iodide is being oxidized from a state of -1 to 0. It is providing electrons for the bromine to aid aiding in its reduction.
3.) Solid lead (II) carbonate is added to a 0.5 M solution of sulfuric acid.
PbCO3(s) + H2SO4(aq) --> PbSO4(s) + H2O(l) + CO2(g)
carbonate plus an acid
PbCO3 + H+ + HSO4
- --> PbSO4 + H2O + CO2
Practice II
The mass of the material in the test tube in which this reaction may occur would be less than before the reaction as the gas produced would escape and not be accounted for.
1.) A mixture of powdered iron (III) oxide and powdered aluminum metal is heated strongly S.R. (thermite reaction!!)
Fe2O3 + 2Al --> Al2O3 + 2Fe
Practice III
A negative value for the change in enthalpy means that the reaction is exothermic and energy is released as the reaction occurs. Therefore the energy needed to break the bonds of the reactants must be less than the energy released as the bonds in the product are made.
2.) Methylamine gas is bubbled into distilled water.
CH3NH2 + H2O --> OH- + CH3NH3+
B-L weak acid/base
Practice III
Phenolphthalein is pink is the presence of a base. Methylamine produces hydroxide ions in solution as it reacts with water and behaves like a base. Therefore, a drop of phenolphthalein into this sol’n would turn pink.
3.) Carbon dioxide gas is passed over hot, sodium oxide.
CO2 + Na2O --> Na2CO3
(synthesis, seen as a reverse decomp.)
Practice III
The sign on S° would be negative because the reactants contain a gas and a solid while the products contain only a solid. Gases are more entropic than solids and so the entropy of the system in decreasing.
1.) A small piece of calcium metal is added to hot distilled water.
Practice IV
Ca + 2H2O --> Ca(OH)2 + H2
2.) Butanol is burned in air.
C4H9OH + 6O2 --> 5H2O + 4CO2
S.R., redox
combustion
Ca + 2H2O --> Ca2+ + 2OH- + H2
or
3.) Excess concentrated ammonia solution is added to a solution of nickel (II) sulfate.
4NH3(aq) + NiSO4(aq) --> Ni(NH3)42+
(aq) + SO42-
(aq)
4.) A solution of copper (II) chloride is added to a solution of sodium sulfide. CuCl2(aq)
+ Na2S(aq) --> CuS(s) + 2NaCl(aq)
complex ion formation
PPT
4NH3 + Ni2+ --> Ni(NH3)42+
Cu2+ + 2Cl- + 2Na+ + S2- --> CuS + 2Na+ + 2Cl-
Cu2+ + S2- --> CuS
4NH3 + Ni2+ + SO42- --> Ni(NH3)4
2+ + SO42-
Practice IV
5.) A solution of tin (II) nitrate is added to a solution of silver nitrate. redox
Sn2+ + 2Ag+ --> Sn4+ + 2Ag
Practice IV
redox6.) Carbon monoxide gas is passed over hot iron (III) oxide.
3CO + Fe2O3 --> 3CO2 + 2Fe
Calcium chloride is heated strongly in the presence of oxygen.
Bonus #1
synthesis…(can be seen a reverse decomposition)
CaCl2 + 3O2 --> Ca(ClO3)2
Acetic acid solution is combined with a sodium hydroxide solution
Bonus#2
acid/base
HC2H3O2 + OH- --> H2O + C2H3O2-
A solution of aluminum nitrate in an excess of sodium hydroxide
Bonus#3
complex ion formation
Al3+ + 4OH- --> Al(OH)4
-
A solution of silver nitrate and a solution of magnesium chloride are combined
Bonus#4
PPT
Ag+ + Cl- --> AgCl
Magnesium oxide is combined with water
Bonus#5
basic anhydride
MgO + H2O -->Mg2+ + 2OH-
or
MgO + H2O --> Mg(OH)2
Strontium hydroxide is heated over a flame.
Bonus#6
decomposition
Sr(OH)2 --> SrO + H2O
Bonus#7
A solution of sodium dichromate is added to an acidified solution of nickel (II) nitrate
14H+ + Cr2O7
2- + 6Ni2+ -->
6Ni3+ + 2Cr3+ + 7H2O
Redox (in acid environment)
A solution of silver nitrate is poured over a coil of copper wire.
Bonus#8
S.R. or redox
2Ag+ + Cu --> Cu2+ + 2Ag
Excess concentrated ammonia solution is added to a solution of cobalt (II) nitrate
Bonus#9
Complex ion formation
4NH3 + Co2+ --> Co(NH3)42+
Phosphorous (V) oxide is placed in water.
Bonus#10
acidic anhydride
P2O5 + 3H2O --> 2H3PO4
A solution of potassium permanganate is added to an acidic solution of ferrous nitrate
Bonus#11
redox in acid environment
8H+ + MnO4- + 5Fe2+ -->
5Fe3+ + Mn2+ + 4H2O
A dilute solution of sodium hydroxide is added to a dilute solution of hydrogen phosphate.
Bonus#12
acid / base
OH- + H3PO4 --> H2O + H2PO4
-
Propanone is burned in airBonus#13
combustion
C3H6O + 4O2 --> 3CO2 + 3H2O
CH3COCH3 + 4O2 --> 3CO2 + 3H2O
or
Solid zinc carbonate is added to 1.0 M sulfuric acid
Bonus #14
carbonate and an acid
ZnCO3+ H+ + HSO4- -->
Zn2+ + SO42- + CO2 + H2O
Calcium is burned in airBonus#15
Synthesis or combustion (but not a hydrocarbon fuel)
2Ca + O2 --> 2CaO
Hydrogen iodide solution reacts with a solution of lithium hydroxide.
Bonus#16
strong acid/strong base
H+ + OH- --> H2O