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Advanced Placement Chemistry, SCH4UAP
EXAMINATION
REVIEW
Equations
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4.2 - Precipitation Reactions
Question 1
Give the formulas to show the reactants and the products for each 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.
a) A solution of copper(II) sulfate is added to a solution of barium hydroxide.
exam]
b) Solutions of strontium nitrate and sodium sulphate are mixed.
[1991
[2001 exam]
c) A solution of copper(II) chloride is added to a solution of sodium sulphide [2000 exam]
d) Solutions of sodium iodide and lead nitrate are mixed
[1990 exam]
e) Solutions of tri-potassium phosphate and zinc nitrate are mixed.
[1993 exam]
f) Solutions of silver nitrate and lithium bromide are mixed. [1989 exam]
Answers to Question 1
a) Cu + OH- Æ Cu(OH)2
b) Sr2+ + SO42- Æ SrSO4
c) Cu2+ + S2- Æ CuS
d) Pb2+ + I- Æ PbI2
2+
e) Zn + PO43- Æ Zn3(PO4)2
f) Ag+ + Br- Æ AgBr
2+
Question 2
[AP, 1984]
The net ionic equation for the reaction between silver carbonate and hydrochloric acid is:
(A) Ag2CO3(s) + 2 H+ + 2 Cl¯ ---> 2 AgCl(s) + H2O + CO(g)
(B) 2 Ag+ + CO32¯ + 2 H+ + 2 Cl¯ ---> 2 AgCl(s) + H2O + CO2(g)
(C) CO32¯ + 2 H+ ---> H2O + CO2(g)
(D) Ag+ + Cl¯ ---> AgCl(s)
(E) Ag2CO3(s) + 2 H+ ---> 2Ag+ + H2CO3
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16.2 - Strong and Weak Acids and Bases
Strong and Weak Acids
A small percentage of all acids are considered to be strong acids, acids that are completely
ionized in aqueous solution.
All of the remaining common acids are weak acids, meaning that, when they are dissolved in
water, only a small percentage of the molecules dissociate into ions.
Strong acids are strong electrolytes; weak acids are weak electrolytes.
LEARN the “Big Six” Strong Acids
HClO4 (perchloric acid)
HNO3 (nitric acid)
HCl, HBr, HI
(hydrochloric, hydrobromic, and hydroiodic acids)
H2SO4
(sulphuric acid)
As far as the AP Chemistry course is concerned, these six are the only strong acids that you are
required to know. Since they completely ionize, they should always be written in ionic form in
an equation (either as reactants or as products).
It is safe to assume that any other acid that you come across in this course will be a weak (or
‘moderate’) acid and it should, therefore, be written in molecular, rather than ionic, form. Two
common examples of moderate acids that you should know are:
H3PO4 (phosphoric acid)
(COOH)2
(oxalic acid)
Page 11
By definition, the strong acids are 100% ionized in aqueous solution and should, therefore,
always be written in ionic, rather than molecular, form. In other words, strong acids should be
written as represented on the right hand side of the following equations:
(perchloric acid)
(nitric acid)
(hydrochloric acid)
(hydrobromic acid)
(hydroiodic acid)
(sulphuric acid)
HClO4(aq) + H2O(l) ---> H3O+(aq) + ClO4-(aq)
HNO3(aq) + H2O(l) ---> H3O+(aq) + NO3-(aq)
HCl(aq) + H2O(l) ---> H3O+(aq) + Cl-(aq)
HBr(aq) + H2O(l) ---> H3O+(aq) + Br-(aq)
HI(aq) + H2O(l) ---> H3O+(aq) + I-(aq)
H2SO4(aq) + 2 H2O(l) ---> 2 H3O+(aq) + SO42-(aq)
By definition, the weak acids are only slightly ionized in aqueous solution and should, therefore,
always be written in molecular, rather than ionic, form. In other words, they should be written as
represented on the left hand side of the following equations (note the double arrows!):
(hydrofluoric acid) HF(aq) + H2O(l) <--> H3O+(aq) + F-(aq)
(carbonic acid)
H2CO3(aq) + 2 H2O(l) <--> 2 H3O+(aq) + CO32-(aq)
(phosphoric acid)
H3PO4(aq) + 3 H2O(l) <--> 3 H3O+(aq) + PO43-(aq)
The majority of weak acids are organic (carboxylic) acids.
YOU WILL LEARN A LOT MORE ABOUT WEAK ACIDS LATER IN THIS UNIT!
It is worth remembering at this time that acidic solutions are also created by certain substances
that react with water to form H+(aq)ions.
You have already learned that non-metal oxides react with water to form acidic solutions. For
example:
SO2(g) + H2O(l) Æ SO32-(aq) + 2H+(aq)
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Strong and Weak Bases
Strong bases are bases that produce a high concentration of OH-(aq) ions in aqueous solution.
As with strong acids, there are also relatively few common strong bases.
Soluble hydroxides and soluble carbonates will produce strong bases.
Since most hydroxides have low solubilities, very few hydroxides form strong bases. The
hydroxides of the Group IA Alkali Metals have high solubilities and, therefore, produce
strong bases; Ba(OH)2 and Sr(OH)2 are moderately soluble hydroxides that produce
moderately strong bases.
Learn these five important Strong Bases:
LiOH, NaOH, KOH, Ba(OH)2, Sr(OH)2
Soluble carbonates (which, for all practical purposes, means the carbonates of the Group
IA Alkali metals also produce moderately strong bases when dissolved in water since the
carbonate ion reacts with water molecules according to the equation:
CO32-(aq) + H2O(l) ----> HCO3-(aq) + OH-(aq)
Strongly basic solutions are also created by certain substances that react with water to form OH–
(aq)ions. The most common of these contain the oxide ion. You have already learned that metal
oxides react with water to form basic solutions. For example:
K2O(s) + H2O(l) Æ 2 K+(aq) + 2 OH-(aq)
Ionic hydrides also react with H2O to form OH–. For example:
LiH + H2O ---> Li+ + OH- + H2
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AP Question
Give the formulas to show the reactants and the products for each 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.
1. Solid cesium oxide is added to water.
[2002, Form A]
2. Sulphur dioxide gas is bubbled into a beaker of water.
[2002, Form B]
3. Solid calcium hydride is added to distilled water.
[1995]
4. Phosphorous(V) oxide powder is sprinkled over distilled water.
5. Sulfur trioxide gas is added to excess water.
[1988]
6. Powdered strontium oxide is added to distilled water.
[2000]
7. Calcium oxide powder is added to distilled water.
[1999]
8. Solid sodium oxide is added to distilled water.
[1998]
9. Drops of liquid dinitrogen trioxide are added to distilled water.
10. Solid lithium hydride is added to water.
[1994]
[1996]
[1992]
11. Samples of boron trichloride gas and ammonia gas are mixed.
[1989]
Answers
1.
Cs2O + H2O Æ Cs+ + OH- (Note: Alkali metal hydroxides are soluble)
2.
SO2 + H2O Æ H2SO3 (Note: H2SO3 is a weak acid and is written in molecular, not ionic, form)
3.
CaH2 + H2O --> Ca(OH)2 + H2 (Note: Ca(OH)2 is only slightly soluble!)
4.
P4O10 + H2O ---> H3PO4 (Note: H3PO4 is a moderateacid and is written in molecular, not ionic, form)
5.
SrO + H2O Æ Sr2+ + OH- (or Sr(OH)2 since it is not very soluble!)
6.
CaO + H2O Æ Ca(OH)2 (Note: Ca(OH)2 is only slightly soluble!)
7.
Na2O + H2O Æ Na+ + OH- (Note: Alkali metal hydroxides are soluble)
8.
N2O3 + H2O ---> HNO2 (Note: HNO2 is a weak acid and is written in molecular, not ionic, form)
9.
LiH + H2O ---> Li+ + OH- + H2
10. BCl3 + NH3 ---> Cl3BNH3
11. SO3 + H2O Æ H+ + SO42- (Note: H2SO4 is a strong acid and is written in ionic, not molecular, form)
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Equations for Reactions Involving Metals
Reaction of Metals with Nonmetals
Such reactions are examples of Combination Reactions. They are also Redox Reactions
(later in the course!).
For example:
Zn + I2 Æ
Note:
When reactions occur between metals such as Fe, Cu, & Sn that can form multiple
ions (Fe2+ & Fe3+; Cu+ & Cu2+; Sn2+ & Sn4+, etc.) and reactive nonmetals, such as O2,
Cl2 & F2 , the metal will always be oxidised to the ion with the higher positive
charge.
For example:
Fe + Cl2 Æ
Reaction of Metals with Water (or Steam)
•
•
The metal atoms are oxidized to metal ions.
The water molecules are reduced (2H2O + 2e- ---> 2OH- + H2)
For example....
Na + H2O --->
Ca + H2O --->
+ OH- + H2
+ OH- + H2
Reaction of Metals with Dilute Acids
•
•
•
The metal atoms are oxidized to metal ions.
The hydrogen ions in the acid are reduced (2H+ + 2e- ---> H2)
The anions in the acid are spectator ions.
For example....
Na + H+ ---> Na+ + H2
Ca + H+ ---> Ca2+ + H2
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Reaction of Metals with Metal Salt Solutions (Single Displacement Reactions)
•
•
•
The metal atoms are oxidized to metal ions.
The metal ions are reduced to metal atoms.
The anions combined originally with the metallic cations are spectator ions.
For example....
Cu + Ag+ ---> Cu2+ + Ag
Al + Cu2+ ---> Al3+ + Cu
(Special) Reactions involving Fe2+ and Fe3+ ions
Fe(s) + 2 Fe3+(aq) ----> 3 Fe2+(aq)
Fe2+(aq) + Cl2(aq) ----> Fe3+(aq) + 2 Cl-(aq)
Page 26
Questions
Give the formulas to show the reactants and the products for the following chemical
equations. 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.
a) Pure solid phosphorus (white form) is burned in air.
b) Calcium metal is strongly heated in nitrogen gas.
c) A piece of aluminum metal is added to a solution of silver nitrate.
d) A small piece of calcium metal is added to hot distilled water (2000).
e) Zinc metal is added to a solution of copper(II) nitrate.
f) A mixture of powdered iron (III) oxide and powdered aluminum is heated
strongly (1999)
ANSWERS
a.
b.
c.
d.
e.
f.
P4 + O2 Æ P4O10
Ca + N2 ---> Ca3N2
Al + Ag+ ----> Al3+ + Ag
Ca + H2O Æ Ca2+ + H2 + OHZn + Cu2+ Æ Zn2+ + Cu
Fe2O3 + Ao Æ Fe + Al2O3
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Name: ___________________________________
AP Chemistry Chemical Equations Worksheet
Write the balanced chemical equation (excluding spectator ions) underneath each reaction description, and answer the question.
(a) A solution of ammonia is added to a dilute
solution of acetic acid.
Identify the conjugate acid–base pairs in this reaction.
(b) Solutions of sodium hydroxide and acetic acid are
mixed.
Acetic acid is a weak acid. If equal volumes of equal
molar solutions are mixed, will the solution pH be >7, 7,
or <7? Explain.
(c) Hydrogen sulfide gas is bubbled through excess
potassium hydroxide solution.
Write the successive ionization equations for H2S.
(d) Solid barium oxide is added to distilled water.
Is the resulting solution acidic, basic or neutral? Explain.
(e) Solid calcium oxide is exposed to a stream of
carbon dioxide gas.
What type of reaction has occurred?
(f) Solid dinitrogen pentoxide is added to water.
Is the final solution acidic, basic or neutral? Explain.
(g) Carbon disulfide vapor is burned in excess oxygen.
What is the oxidizing agent in this reaction?
–1–
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(h) Lithium metal is burned in air.
Besides combustion, what type of reaction could this be
classified as?
(i) A solution of diamminesilver(I) chloride is treated
with dilute nitric acid.
What is the driving force for this reaction?
(j) A concentrated solution of ammonia is added to a
suspension of zinc hydroxide.
What are the possible molecular geometries for the complex ion product?
(k) Excess concentrated sodium hydroxide solution is
added to solid aluminum hydroxide.
Name any complex ion formed in the reaction.
(l) Solid ammonium carbonate is heated.
Classify the type of reaction occurring.
(m) A solution of hydrogen peroxide is catalytically
decomposed.
Name the element being reduced and the element being
oxidized.
(n) A solution of potassium iodide is electrolyzed.
At which electrode would a gas be released?
(o) A solution of copper(II) sulfate is electrolyzed using
inert electrodes.
Is the final solution acidic, basic or neutral?
(p) A solution of ammonium sulfate is added to a saturated solution of barium hydroxide.
Identify any precipitate formed in the reaction.
(q) A solution of copper(II) chloride is added to a solution of sodium sulfide.
Name the spectator ions in this reaction.
(r) Solutions of manganese(II) sulfate and ammonium
sulfide are mixed.
List any precipitate that forms during the reaction.
–2–
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(s) Solutions of silver nitrate and sodium chromate are
mixed.
What is the oxidation number of chromium in the chromate ion?
(t) Glacial acetic acid is mixed with liquid methanol
(nonaqueous).
What type of organic reaction can this be
characterized as?
(u) Chlorine gas is bubbled into a cold, dilute solution of
potassium hydroxide.
What element is undergoing oxidation and what element
is undergoing reduction?
(v) A strip of copper is immersed in a concentrated
nitric acid solution.
List at least two observations that indicate a chemical
reaction is occurring.
(w) Hydrogen gas is passed over hot iron(II) oxide
powder.
What is the oxidation number of the hydrogen in hydrogen gas?
(x) Acidified potassium permanganate is added to a
solution of sodium nitrite.
Write and balance the oxidation half-reaction for mass
and charge.
(y) A solution of sodium bromide is added to an acidified solution of potassium bromate.
Write and balance the reduction half-reaction for mass
and charge.
(z) Aluminum metal is added to a solution of copper(II)
chloride.
List at least two observations that indicate a chemical
reaction is occurring.
(aa) Excess chlorine gas is passed over hot iron filings.
What type of reaction is occurring?
(bb) Magnesium metal is added to nitrogen gas.
What is the oxidation number of magnesium before and
after the reaction?
–3–
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(cc) Solid lithium hydride is added to distilled water.
Is the final solution acidic, basic or neutral? Explain.
(dd) Benzene is treated with bromine in the presence of a
catalyst.
Classify the type of organic reaction that takes place.
(ee) Solid lithium oxide is added to excess water.
Is the final solution acidic, basic or neutral? Explain.
(ff) Solid potassium chlorate is heated in the presence of
manganese dioxide as a catalyst.
How many moles of reaction products can be produced
from one mole of potassium chlorate?
(gg) Dilute hydrochloric acid is added to a solution of
potassium sulfite.
List all spectator ions.
(hh) A solution of sulfuric acid is added to a solution of
barium hydroxide until the same number of moles of
each compound has been added.
Is the final solution acidic, basic or neutral? Explain.
.
(ii) A mixture of solid calcium oxide and solid tetraphosphorus decaoxide is heated.
Is the product compound(s) soluble in water?
(jj) Sulfur dioxide gas is passed over solid calcium
oxide.
Name the product compound(s).
(kk) Solid zinc sulfide is heated in an excess of oxygen.
(ll) A solution of potassium iodide is added to an acidified solution of potassium dichromate.
What change in oxidation state does sulfur undergo in this
reaction?
What is the reducing agent in this reaction?
–4–
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AP Chemistry Chemical Equations Worksheet
Answer Key
Changes to the AP Chemistry Exam format for 2007 include modification to Question 4 in Section II. Previously, students
were asked to write chemical equations for any five of eight given sets of chemical reactions. The new format requires students
to write balanced chemical equations showing only the reacting substances (excluding spectator ions) for three different sets
of reactants and to answer a short question (requiring no calculator) about each reaction. The questions are intended to test the
students’ understanding of the meaning of the reactions.
The College Board has provided only a few examples of the types of questions that might be asked. (Visit the College
Board Web site at www.apcentral.collegeboard.com/apc/public/courses/150180.html?type=print for examples.) AP Chemistry
teachers have asked us if we have any products or worksheets to address this new format. The following list of practice
chemical equations is provided as a helpful tool to assist teachers. We have compiled these questions based on our interpretation of the questions on the College Board Web site. Flinn Scientific has no additional information or guidance other than that
provided by the College Board on its Web site.
In each of the 38 reactions listed below, a representative question about the reaction and the answer to the question are
included, along with the balanced chemical equation. We hope that you will find this worksheet helpful in preparing students
for the new AP Chemistry chemical equation section.
(a) A solution of ammonia is added to a dilute
solution of acetic acid.
NH3 + CH3COOH → NH4 + CH3
+
COO–
(b) Solutions of sodium hydroxide and acetic acid are
mixed.
OH– + CH3COOH → H2O + CH3COO–
(c) Hydrogen sulfide gas is bubbled through excess
potassium hydroxide solution.
H2S +
2OH–
→
S2–
+ 2H2O
(d) Solid barium oxide is added to distilled water.
BaO + H2O →
Ba2+
+
2OH–
(e) Solid calcium oxide is exposed to a stream of
carbon dioxide gas.
Identify the conjugate acid–base pairs in this reaction.
Answer: NH3 (base) and NH4+ (acid)
CH3COOH (acid) and CH3COO– (base)
Acetic acid is a weak acid. If equal volumes of equal
molar solutions are mixed, will the solution pH be >7, 7,
or <7? Explain.
Answer: >7. The salt of a weak acid (CH3COO–) is
basic in solution.
Write the successive ionization equations for H2S.
–
+
Answer: H2S + H2O ←
→ HS + H3O
2–
+
HS– + H O ←
→ S + HO
2
3
Is the resulting solution acidic, basic or neutral? Explain.
Answer: Basic. Metal oxides form basic compounds in
water.
What type of reaction has occurred?
Answer: A synthesis (or combination) reaction.
CaO + CO2 → CaCO3
(f) Solid dinitrogen pentoxide is added to water.
N2O5 + H2O → 2H+ + 2NO3–
(g) Carbon disulfide vapor is burned in excess oxygen.
CS2 + 3O2 → CO2 + 2SO2
Is the final solution acidic, basic or neutral? Explain.
Answer: Acidic. Nonmetal oxides form acidic compounds in water.
What is the oxidizing agent in this reaction?
Answer: Oxygen.
–5–
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(h) Lithium metal is burned in air.
Besides combustion, what type of reaction could this be
classified as?
4Li + O2 → 2Li2O
Answer: The reaction may be classified as both a synthesis and a redox reaction.
What is the driving force for this reaction?
(i) A solution of diamminesilver(I) chloride is treated
with dilute nitric acid.
Answer: Precipitation of silver chloride.
[Ag(NH3)2]+ + Cl– + 2H+ → AgCl + 2NH4+
(j) A concentrated solution of ammonia is added to a
suspension of zinc hydroxide.
What are the possible molecular geometries for the complex ion product?
4NH3 + Zn(OH)2 → [Zn(NH3)4]2+ + 2OH–
Answer: All [ML4]n+ complex ions have either a tetrahedral or square planar geometry.
(k) Excess concentrated sodium hydroxide solution is
added to solid aluminum hydroxide.
Name any complex ion formed in the reaction.
Answer: Tetrahydroxoaluminate.
OH– + Al(OH)3 → [Al(OH4]–
(l) Solid ammonium carbonate is heated.
Classify the type of reaction occurring.
(NH4 )2CO3 → 2NH3 + CO2 + H2O
Answer: This is a decomposition reaction.
(m) A solution of hydrogen peroxide is catalytically
decomposed.
Name the element being reduced and the element being
oxidized.
2H2O2 → 2H2O + O2
Answer: Oxygen is being both reduced and oxidized.
(n) A solution of potassium iodide is electrolyzed.
At which electrode would a gas be released?
2I– + 2H2O → I2 + H2 + 2OH–
Answer: Hydrogen gas is released at the cathode (the
negative electrode).
(o) A solution of copper(II) sulfate is electrolyzed using
inert electrodes.
Is the final solution acidic, basic, or neutral?
Answer: Acidic hydrogen ions (H+) are produced in the
reaction.
2Cu2+ + 2H2O → 2Cu + O2 + 4H+
(p) A solution of ammonium sulfate is added to a saturated solution of barium hydroxide.
Identify any precipitate formed in the reaction.
NH4+ + SO42– + Ba2+ + 2OH– →
BaSO4 + NH3 + 2H2O
(q) A solution of copper(II) chloride is added to a solution of sodium sulfide.
Cu2+
+
S2–
Answer: Barium sulfate, BaSO4.
Name the spectator ions in this reaction.
Answer: The chloride ion, Cl–, and the sodium ion, Na+.
→ CuS
(r) Solutions of manganese(II) sulfate and ammonium
sulfide are mixed.
List any precipitate that forms during the reaction.
Answer: Manganese(II) sulfide, MnS.
Mn2+ + S2– → MnS
–6–
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(s) Solutions of silver nitrate and sodium chromate are
mixed.
What is the oxidation number of chromium in the chromate ion?
2Ag+ + CrO42– → Ag2CrO4
Answer: +6.
What type of organic reaction can this be
characterized as?
(t) Glacial acetic acid is mixed with liquid methanol
(nonaqueous).
CH3COOH + CH3OH → CH3COOCH3 + H2O
Answer: An esterification reaction.
(u) Chlorine gas is bubbled into a cold, dilute solution of
potassium hydroxide.
Cl2 + 2OH– → ClO– + Cl– + H2O
Answer: Chlorine, Cl, is being reduced to –1 (Cl–) and
also being oxidized to +1 in ClO–.
(v) A strip of copper is immersed in a concentrated
nitric acid solution.
List at least two observations that indicate a chemical
reaction is occurring.
Cu + 4H+ + 2NO3– → Cu2+ + 2NO2 + 2H2O
Answer: Solution color changes from colorless to blue.
Bubbles of NO2 gas are observed at the copper
strip. The gas is brown.
What is the oxidation number of the hydrogen in hydrogen gas?
(w) Hydrogen gas is passed over hot iron(II) oxide
powder.
H2 + FeO → Fe + H2O
Answer: Zero—the oxidation number of an atom in its
elemental form is zero.
(x) Acidified potassium permanganate is added to a
solution of sodium nitrite.
Write and balance the oxidation half-reaction for mass
and charge.
2MnO4– + 6H+ + 5NO2– →
2Mn2+ + 3H2O + 5NO3–
(y) A solution of sodium bromide is added to an acidified solution of potassium bromate.
5Br – + 6H+ + BrO3– → 3Br2 + 3H2O
(z) Aluminum metal is added to a solution of copper(II)
chloride.
2Al + 3Cu2+ → 2Al3+ + 3Cu
(aa) Excess chlorine gas is passed over hot iron filings.
3Cl2 + 2Fe → 2FeCl3
(bb) Magnesium metal is added to nitrogen gas.
3Mg + N2 → Mg3N2
What element is undergoing oxidation and what element
is undergoing reduction?
Answer: H2O + NO2– → NO3– + 2H+ + 2e–
Write and balance the reduction half-reaction for mass
and charge.
Answer: 12H+ + 2BrO3– + 10e– → Br2 + 6H2O
List at least two observations that indicate a chemical
reaction is occurring.
Answer: The aluminum dissolves, a red solid precipitates, the blue color of the solution fades, and
the solution temperature increases.
What type of reaction is occurring?
Answer: A synthesis reaction (or a redox reaction).
What is the oxidation number of magnesium before and
after the reaction?
Answer: Magnesium goes from zero in Mg to +2 in
Mg3N2.
–7–
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(cc) Solid lithium hydride is added to distilled water.
LiH + H2O → Li+ + OH– + H2
(dd) Benzene is treated with bromine in the presence of a
catalyst.
Is the final solution acidic, basic or neutral? Explain.
Answer: Basic. Metallic hydrides react with water to
form metallic hydroxides.
Classify the type of organic reaction that takes place.
Answer: This is a substitution reaction.
Br2 + C6H6 → C6H5Br + HBr
(ee) Solid lithium oxide is added to excess water.
Li2O + H2O → 2Li+ + 2OH–
(ff) Solid potassium chlorate is heated in the presence of
manganese dioxide as a catalyst.
MnO2
2KClO3 ⎯⎯→
2KCl + 3O2
(gg) Dilute hydrochloric acid is added to a solution of
potassium sulfite.
Is the final solution acidic, basic or neutral? Explain.
Answer: Basic. Soluble metal oxides react in water to
form bases (metallic hydroxides).
How many moles of reaction products can be produced
from one mole of potassium chlorate?
Answer: 2½ moles.
List all spectator ions.
Answer: Potassium, K+, and chloride, Cl–.
2H+ + SO32– → H2O + SO2
(hh) A solution of sulfuric acid is added to a solution of
barium hydroxide until the same number of moles of
each compound has been added.
2H+ + SO42– + Ba2+ + 2OH– → BaSO4 + 2H2O
(ii) A mixture of solid calcium oxide and solid tetraphosphorus decaoxide is heated.
6CaO + P4O10 → 2Ca3(PO4)2
(jj) Sulfur dioxide gas is passed over solid calcium
oxide.
Is the final solution acidic, basic or neutral? Explain.
Answer: Neutral. The neutralization of a strong base
[Ba(OH)2] by a strong acid [H2SO4] yields a
neutral solution.
Is the product compound(s) soluble in water?
Answer: No. Phosphates other than those of group 1
elements and NH4+ are insoluble.
Name the product compound(s).
Answer: Calcium sulfite.
SO2 + CaO → CaSO3
(kk) Solid zinc sulfide is heated in an excess of oxygen.
2ZnS + 3O2 → 2ZnO + 2SO2
What change in oxidation state does sulfur undergo in this
reaction?
Answer: Sulfur starts out as –2 in ZnS and ends up as
+4 in SO2. The charge is +6.
(ll) A solution of potassium iodide is added to an acidified solution of potassium dichromate.
6I– + 14H+ + Cr2O72– → 3I2 + 2Cr 3+ + 7H2O
What is the reducing agent in this reaction?
Answer: The species that undergoes oxidation, in this
case iodide ion, I–, is the reducing agent.
–8–
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