AP chemistry chemical Equations worksheetAnswer Key

changes to the AP Chemistry Exam format for 2007 include modification to euestion 4 in Section II. previously, studentswere asked to write chemical equations for any five of eight given sets of chemical ieactions. The new format requires studentsto write balanced chemical equations showin! only the i"u"ting substances (excluding spectator ions) for three different setsofreactants and to answer a short question 1reluiring no calculior) about each reaction. The questions are intended to test thesrudents' understanding of the meaning ofthe rlacdons.

Board has provided only a few examples of the types of questions that might be asked. (visit the Collegeint for examples.) AP Chemistry

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:1"Tr"1^":::*::S-0t".-*0..u. u l"lof:l,-"1 to assisr reachers. we have compired these questions based o, or. irnterpreta-tion of the questions on the College Board web site. Flinn Scientin. r,uslo ;ffioii;;;il;;; ion or guidance other than thatprovided by the College Board on its Web site.

The CollegeBoard Web site at

In each of the 38 reactions listed below, a representative question about the reaction and the answer to the question areincluded' along with the balanced chemical "quutior.

we hope that you will irnd this worksheet helpful in preparing studentsfor the new AP Chemistry chemical equation section.

(a) A solution of ammonia is added to a dilutesolution of acetic acid.

NH, + CH3COOH -> NHo+ + CH.COO-

Identify the conjugate acid-base pairs in this reaction.

Answer: NH, (base) and NHo* (acid)

CH3COOH (acid) and CHTCOO- (base)

(b) Solutions ofsodium hydroxide and acetic acid aremixed.

OH- + CH3COOH + ILO + CHTCOO-

Acetic acid is a weak acid. If equal volumes of equalmolar solutions are mixed, will the solution pHbe >7,7,or <7? Explain.

Answer: >7. The salt of a weak acid (CH.COOJ isbasic in solution.

(c) Hydrogen sulfide gas is bubbled through excesspotassium hydroxide solution.

HrS + 2OH- -+ 32- + ZHrO

Write the successive ionization equations for HrS.

Answer: HrS + HzO S HS- + HrO+

HS-+HrOg52-+HrO+(d) Solid barium oxide is added to distilled water.

BaO + HrO -+ Ba2+ + 2OH-

Is the resulting solution acidic, basic or neutral? Explain.

Answer: Basic. Metal oxides form basic compounds inwater.

(e) Solid calcium oxide is exposed to a stream ofcarbon dioxide gas.

CaO + CO, -+ CaCO,

What type of reaction has occurred?

Answer: A synthesis (or combination) reaction.

(0 Solid dinitrogen pentoxide is added ro water.

NrO, + HrO - 2H+ + 2NO3-

Is the hnal solution acidic, basic or neutral? Explain.

Answer: Acidic. Nonmetal oxides form acidic com_pounds in water.

(g) Carbon disulfide vapor is burned in excess oxygen.

CS, + 3C., -+ CO, + 2SO,

What is the oxidizing agent in this reaction?

Answer: Oxygen.

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(h) Lithium metal is burned in air.

4Li + O, -+ 2LirO

Besides combustion, what type of reaction could this beclassified as?

Answer: The reaction may be classified as both a syn-thesis and a redox reaction.

(r) A solution of diamminesilver(I) chloride is treatedwith dilute nitric acid.

[Ag(NH3)2J* + Cl- + 2H+ --s AgCl + 2NH4+

What is the driving force for this reaction?

Answer: Precipitation of silver chloride.

0) A concentrated solution of ammonia is added to asuspension of zinc hydroxide.

4NH, + Zn(OH), -+ [Zn(NH.) oJ2* + zOH-

What are the possible molecular geometries for the com-plex ion product?

Answer: All [ML4]'+ complex ions have either a tetra-hedral or square planar geometry.

(k) Excess concentrated sodium hydroxide solution isadded to solid aluminum hydroxide.

OH- + AI(OH)3 -+ [Al(OHoJ-

Name any complex ion formed in the reaction.

Answer: Tetrahydroxoaluniinate.

0) Solid ammonium carbonate is heated.

(NH4)2CO3 -+ 2NH3 + CO, + HrO

Classify the type ofreaction occurring.

Answer: This is a decomposition reaction.

(m) A solution of hydrogen peroxide is catalyticallydecomposed.

2HzO2 -+ 2HrO + O,

Name the element being reduced and the element beingoxidized-

Answer: Oxygen is being both reduced and oxidized.

(n) A solution ofpotassium iodide is electrolyzed.

2I- + ZHrO -+ I, + H, + 2OH-

At which electrode would a gas be released?

Answer: Hydrogen gas is released at the cathode (thenegative electrode).

(o) A solution ofcopper(Il) sulfate is electrolyzed usinginert electrodes.

2Cu2* + 2\O --+ 2Cu + O, + 4H+

Is the final solution acidic, basic, or neutral?

Answer: Acidic hydrogen ions (H+) are produced in thereaction.

(p) A solution of ammonium sulfate is added to a saru-rated solution of barium hydroxide.

2NH4+ + SOo2- + Baz+ + 2OH- -+

BaSOo+2NHr+ZHrO

Identifu any precipitate formed in the reaction.

Answer: Barium sulfate, BaSOo.

(q) A solution ofcopper(Il) chloride is added ro a solu-tion of sodium sulfide.

Cu2* + 52- -+ CuS

Name the spectator ions in this reaction.

Answer: The chloride ion, Cl-, and the sodium ion, Na+

(r) Solutions of manganese(Il) sulfate and ammoniumsulfide are mixed.

Mn2* + S2- -+ MnS

List any precipitate that forms during the reaction.

Answer: Manganese(Il) sulfide, MnS.

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(s) Solutions of silver nitrate and sodium chromate aremixed.

2Ag++CrOo2-+AgrCrOo

What is the oxidation number of chromium in the chro-mate ion?

Answer: +6.

(t) Glacial acetic acid is mixed with liquid merhanol(nonaqueous).

CH3COOH + CH3OH -+ CHTCOOCH, + HrO

What type of organic reaction can this becharacterized as?

Answer: Anesterificationreaction.

(u) Chlorine gas is bubbled into a cold, dilute solution ofpotassium hydroxide.

Cl, + 2OH- -+ CIO- + Cl- + HrO

What element is undergoing oxidation and what elementis undergoing reduction?

Answer: Chlorine, Cl, is being reduced to -1 (Cl-) and

also being oxidized to +1 in CIO-.

(v) A strip of copper is immersed in a concentratednitric acid solution.

Cu + 4H+ + 2NO3- -+ Cu2* + 2NO, + 2HrO

List at least two observations that indicate a chemicalreaction is occurring.

Answer: Solution color changes from colorless to blue.Bubbles of NO, gas are observed at the copperstrip. The gas is brown.

(w) Hydrogen gas is passed over hot iron(Il) oxidepowder.

Hr+FeO+Fe+HrO

What is the oxidation number of the hydrogen in hydro-gen gas?

Answer: Zero--the oxidation number of an atom in itselemental form is zero.

(x) Acidified potassium permanganate is added to asolution of sodium nitrite.

2MnOl + 6H+ + 5NO; -+2Mn2*+3lLo+5Nor-

Write and balance the oxidation half-reaction for massand charge.

Answer: HrO + NO; -+ NOr- + 2H+ + 2e-

. (y) A solution of sodium bromide is added to an acidi-fied solution of potassium bromate.

5Br- + 6H+ + BrOr- -+ 3Br, + 3HrO

Write and balance the reduction half-reaction for massand charge.

Answer: 12H+ + 2BrOr- + l0e- -) Br2 + 6HrO

(z) Aluminum metal is added to a solution of copper(Il)chloride.

2Al+3Cu2+--)2Al3++3Cu

List at least two observations that indicate a chemicalreaction is occurring.

Answer: The aluminum dissolves, a red solid precipi-tates, the blue color ofthe solution fades, andthe solution temperature increases.

(aa) Excess chlorine gas is passed over hot iron filings.

3Cl, + ZFe -s 2FeCl,

What type of reaction is occurring?

Answer: A synthesis reaction (or a redox reaction).

(bb) Magnesium metal is added to nitrogen gas.

3Mg + N, -+ MgrN,

What is the oxidation number of magnesium before andafter the reaction?

Answer: Magnesium goes from zero in Mg to +2 inMgrNz.

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(cc) Solid lithium hydride is added to distilled water.

LiH + HrO -r Li+ + OH- + H,

Is the final solution acidic, basic or neuffal? Explain.

Answer: Basic. Metallic hydrides react with water toform metallic hydroxides.

(dd) Benzene is treated with bromine in the presence of a

catalyst.

Brr+CuHu+CuHrBr+HBr

Classify the type of organic reaction that takes place.

Answer: This is a substitution reaction.

(ee) Solid lithium oxide is added to excess water.

LirO + HrO -+ ZLi+ + 2OH-

Is the final solution acidic, basic or neutral? Explain.

Answer: Basic. Soluble metal oxides react in water toform bases (metallic hydroxides).

(fi| Solid potassium chlorate is heated in the presence ofmanganese dioxide as a catalyst.

MnO"

How many moles of reaction products can be producedfromone mole of potassium chlorate?

Answer: 2Vzmoles.

(gg) Dilute hydrochloric acid is added to a solution ofpotassium sulfite.

2H+ + SOr2- -+ HrO + SO,

List all spectator ions.

Answer: Potassium, K+, and chloride, Cl-

(hh) A solution of sulfuric acid is added to a solution ofbarium hydroxide until the same number of moles ofeach compound has been added.

2H+ + SOo2- + Ba2+ + 2OH- -+ BaSoo + zH2o

Is the final solution acidic, basic or neutral? Explain.

Answer: Neutral. The neutralization of a strong base

[Ba(OH)r] by a strong acid [HrSOoJ yields aneutral solution.

(ii) A mixture of solid calcium oxide and solid tetra-phosphorus decaoxide is heated.

6CaO + PoO,o -+ ZCa"(pO)2

Is the product compound(s) soluble in water?

Answer: No. Phosphates other than those of group 1

elements and NHo+ are insoluble.

Cj) Sulfur dioxide gas is passed over solid calciumoxide.

SO, + CaO -+ CaSO,

Name the product compound(s).

Answer: Calciumsulfite.

(kk) Solid zinc sulfide is heated in an excess of oxygen.

ZZ*S + 30, -+ ZZnO + 2SO,

What change in oxidation state does sulfur undergo in thisreaction?

Answer: Sulfur starts out as -2 in ZnS and ends up as

+4 in SOr. The charge is +6.

(11) A solution of potassium iodide is added to an acidi-fied solution of potassium dichromate.

6I- + 14H+ + CrrOr2- --> 311- + 2Cr3* + 7H2O

What is the reducing agent in this reaction?

Answer: The species that undergoes oxidation, in thiscase iodide ion, I-, is the reducing agent.

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