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Chemistry
WAEC / WASSCE 2016
Oxidation, Reduction & Redox Reactions
The oxidation number of sulphur is +4 in
A
Na2S>2O3
B
H2SO3
C
H2SO4
D
SO3
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
No expanded working has been attached for this question yet. The verified answer is Option B.
Source: Myschool Past Questions Archive (Record #45210)
Chemistry
WAEC / WASSCE 2016
Oxidation, Reduction & Redox Reactions
Solution
Consider the following ionic equation:
Cr\(_2\)O\(_7\)\(^{2-}\) + 14H\(^+\) + ne- → 2Cr\(^{3+}\) + 7H\(_2\)O.
The value of n in the equation is_______?
A
7
B
6
C
3
D
2
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
Cr\(_2\)O\(_7\)\(^{2-}\) + 14H\(^+\) + ne- → 2Cr\(^{3+}\) + 7H\(_2\)O.
All you need to do is to balance the chemical equation, balancing the ionic/ number of moles of the electrons on both sides
Cr\(_2\)O\(_7\)\(^{2-}\) + 14H\(^+\) + ne- → 2Cr\(^{3+}\) + 7H\(_2\)O.
(1 x - 2) + (14 x +1) + n = ( 2 x +3)
- 2 + 14 + n = +6
12 + n = + 6
What do we need to the +12 on the left hand side to equate +6 on the right hand side
+12 - 6 = +6
Therefore, number of electrons is 6. i.e 6e\(^-\)
Source: Myschool Past Questions Archive (Record #45212)
Chemistry
WAEC / WASSCE 2016
Oxidation, Reduction & Redox Reactions
Solution
Consider the following half-cell reactions.
Al(s) \(\to\) Al3+(aq) + 3e-
Cu2+(aq) + 2e- \(\to\) Cu(s)
The overall equation for the reaction is
A
Al(s) + Cu2+(aq) \(\to\) Al3+(aq) + Cu(s)
B
2Al(s) + Cu2+(aq) \(\to\) 2Al(aq) + Cu(s)
C
2Al(s) + 3Cu2+(aq) \(\to\) 3Cu(s) + 2Al3+(aq)
D
3Al(s) + 2Cu2+(aq) \(\to\) Cu(s) + 3Al3+(aq)
medium Difficulty
Verified Correct Answer: Option C
Chemical Principles & Mechanism
Al(s) \(\to\) Al3+(aq) + 3e- ______(i)
Cu2+(aq) + 2e- \(\to\) Cu(s) ________(ii)
To balance the electrons, multiply equation (i) by 2 and equation (ii) by 3 and then add the resulting equations
2Al(s) \(\to\)2Al3+(aq) + 3e-
3cu2+(aq) + 6e- \(\to\)3Cu(s)
2Al(s) + 3Cu2+(aq) \(\to\) 3Cu(s) + 2Al3+(aq)
Source: Myschool Past Questions Archive (Record #45216)
Chemistry
WAEC / WASSCE 2016
Organic Chemistry II: Functional Groups, Polymers & Biomolecules
Amino acids are obtained from proteins by
A
Hydrolysis
B
Oxidation
C
Polymerization
D
Reduction
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
No expanded working has been attached for this question yet. The verified answer is Option A.
Source: Myschool Past Questions Archive (Record #45278)
Chemistry
WAEC / WASSCE 2016
Organic Chemistry I: Hydrocarbons & Crude Oil
Solution
When a compound X is heated with concentrated tetraoxosulphate(VI)acid, it produces an alkene. X is an
A
Alkane
B
Alkanol
C
Alkanoate
D
Alkyne
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
When alcohol reacts with concentrated sulphuric acid, H\(_2\)SO\(_4\), it undergoes a dehydration reaction that removes water molecules. The reaction can produce alkenes or ethers, depending on the conditions.
Concentrated sulfuric acid is a strong oxidizing agent that absorbs water. It removes the hydroxyl (OH) group from the alcohol carbon atom and a hydrogen atom from an adjacent carbon atom.
Alkenes: The reaction can produce alkenes, such as ethene, C\(_2\)H\(_4\), when the alcohol loses water molecules.
Ethers: The reaction can produce Ethers, such as diethyl ether, when two alcohol molecules are dehydrated.
Source: Myschool Past Questions Archive (Record #45281)
Chemistry
WAEC / WASSCE 2016
Organic Chemistry I: Hydrocarbons & Crude Oil
Ripening of fruits is hastened by using
A
Ethanol
B
Ethane
C
Ethene
D
Ethyne
medium Difficulty
Verified Correct Answer: Option C
Chemical Principles & Mechanism
No expanded working has been attached for this question yet. The verified answer is Option C.
Source: Myschool Past Questions Archive (Record #45282)
Chemistry
WAEC / WASSCE 2016
Organic Chemistry II: Functional Groups, Polymers & Biomolecules
Solution
The compound that makes palm wine taste sour after exposure to the air for few days is
A
Ethanol
B
Ethanoic acid
C
Methanol
D
Methanoic acid
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
The ethanol (alcohol content) of the wine, is oxidized, by the oxygen in the air into ethanoic acid.
Source: Myschool Past Questions Archive (Record #45284)
Chemistry
WAEC / WASSCE 2016
Organic Chemistry II: Functional Groups, Polymers & Biomolecules
Which of the following compounds is/are secondary alkanols?
i) CH3CH(CH3)CH3OH
ii) CH3CH2CH(OH)CH3
iii) CH3C(OH)(CH3)CH3
A
I only
B
II only
C
I and III only
D
II and III only
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
No expanded working has been attached for this question yet. The verified answer is Option B.
Source: Myschool Past Questions Archive (Record #45287)
Chemistry
WAEC / WASSCE 2016
Organic Chemistry I: Hydrocarbons & Crude Oil
Solution
Consider the following reaction equation
C2H4(g) + 3O2(g) \(\to\) 2CO2(g) + 2H2O(l).
The volume of oxygen at s.t.p that will be required to burn 14g of ethene is
[C2H4 = 28; Molar volume of gas at s.t.p = 22.4dm3
A
64.2dm3
B
33.6dm3
C
11.2dm3
D
3.73dm3
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
C2H4(g) + 3O2(g) \(\to\) 2CO2(g) + 2H2O(l)
1 mole of ethene required 3 moles of O2
28g of ethene required 3 x 22.4dm3 of O2
14g will require \(\frac{14 \times 3 \times 22.4dm^3}{28}\)
= 33.6dm3
Source: Myschool Past Questions Archive (Record #45290)
Chemistry
WAEC / WASSCE 2016
Organic Chemistry I: Hydrocarbons & Crude Oil
Which of the following sources of energy contributes to green-house effect?
A
Natural gas
B
Nuclear
C
Wind
D
Solar
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
No expanded working has been attached for this question yet. The verified answer is Option A.
Source: Myschool Past Questions Archive (Record #45292)
Chemistry
WAEC / WASSCE 2016
Air & Environmental Chemistry
Solution
A consequences of global warming is
A
Air pollution
B
Flooding
C
Increased humidity
D
Water pollution
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
Global warming is a gradual increase in the earth’s temperature generally due to the greenhouse effect caused by increased levels of carbon dioxide, CFCs, and other pollutants., consequences of global warming include: Seasonal/climate change, Rising oceans, Increase in flooding occurrences. Melting ice caps or polar ice. Increase in the average temperature of the world.
Source: Myschool Past Questions Archive (Record #45293)
Chemistry
WAEC / WASSCE 2016
Metals, Transition Elements & Extraction
Which of the following metals is common to both brass and bronze?
A
Aluminium
B
Copper
C
Lead
D
Iron
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
No expanded working has been attached for this question yet. The verified answer is Option B.
Source: Myschool Past Questions Archive (Record #45295)
Chemistry
WAEC / WASSCE 2016
Organic Chemistry II: Functional Groups, Polymers & Biomolecules
The alkanol obtained from the production of soap is
A
Dihydric Alkanol
B
Tertiary Alkanol
C
Trihydric Alkanol
D
Monohydric Alkanol
medium Difficulty
Verified Correct Answer: Option C
Chemical Principles & Mechanism
No expanded working has been attached for this question yet. The verified answer is Option C.
Source: Myschool Past Questions Archive (Record #45297)
Chemistry
WAEC / WASSCE 2016
Nature of Matter & Separation Techniques
Solution
(a) What are nucleons?
(b) State Graham's law of diffusion.
(c) Explain briefly why aluminium does not corrode easily.
(d) State three examples of periodic properties.
(e) State two reasons why real gases deviate from ideal gas behaviour.
(f) List three uses of fractional distillation in industry.
(g) What factors determine the selective discharge of ions at the electrodes during electrolysis?
(h) State the type of reaction represented by each of the following equations:
(i) C\(_2\)H\(_6\) + Br\(_2\) ---> C\(_2\)H\(_5\)Br + HBr;
(ii) C\(_2\)H\(_4\) + .Br\(_2\) ---> CH\(_4\)Br\(_2\)
(i) Name the products formed when butane burns in limited supply of air.
(j) List three methods of separating a solid from a liquid.
medium Difficulty
Verified Correct Answer: Option
Chemical Principles & Mechanism
(a) Nucleons refer to the protons and neutrons that are found in the nucleus OR Nucleons are nuclear particles which are protons and neutrons.
(b) Graham's law of diffusion states that, at constant temperature and pressure, the rate of diffussion of a gas is inversely proportional to the square root of its density or molar mass or vapour density
(c) Aluminum oxide layer forms on the surface of the metal. The oxide layer forms a potective coating layer which does not flake off.
(d) — atomic radius, Ionic radius, ionization energy. —redox potentials, electronegativity, electron affinity. — melting point, boiling point, electrical conductivity.
(e) — Molecules of real gases have significant attractive forces between them.
— The volume of the molecules of real gases is not negligible.
--- Collision between the molecules are not perfectly elastic.
(f) — Separation of crude oil into its components / petroleurn refining. —Purification of ethanol. —Separation of liquefied air
(g) —Position of the ions in the electrochemical series —Concentration of the ions in the electrolyte —Nature of the electrodes used.
(h)(i) Substitution reaction. (ii) Addition reaction.
(i) — Carbon or soot, Carbon two oxide (carbon II oxide), Water.
(j) Filtration, Crystallisation, Evaporation, decantation, centrifugation
Source: Myschool Past Questions Archive (Record #51005)
Chemistry
WAEC / WASSCE 2016
Metals, Transition Elements & Extraction
Solution
(a) Consider the following atoms: \(^R_T\)X; \(^S_T\)X.
(i) State the phenomenon exhibited by the two atoms.
(ii) What is the difference between the atoms?
(iii) Give two examples of elements that exhibit the phenomenon stated in (ai)
(iv) lf T is 17, write the electron configuration of the element
(b)(i) State two differences between metals and-non-metals with respect to their:
I. physical properties;
2. chemical properties.
(ii) Give one example of each for the following compounds:
I. an amphoteric oxide;
II. a hydride which evolves hydrogen when reacted with water;
Ill. a trioxocarbonate (IV) salt which is readily decomposed on heating;
IV. a chloride salt which is readily hydrolyzed in water.
(c)(i) State three characteristic properties of transition metals.
(ii) Write the electron configuration of \(_{30}Zn\)
(iii.) Explain briefly why zinc is not considered as a typical transition element.
(d) Consider the reaction represented by the following equation:- Na\(_2\)CO\(_{3(aq)}\) + MgCl\(_{2(aq)}\) ----> 2NaCl\(_{(aq)}\) + MgCO\(_{3(aq)}\). Calculate the mass of sodium trioxocarbonate (IV) needed to produce 3.36 of magnesium trioxocarbonate (IV). [C = 12.0, O = 16.0, Na = 23.0, Mg = 24:0 ]
medium Difficulty
Verified Correct Answer: Option
Chemical Principles & Mechanism
(a)(i) Isotopy
(ii) They have different mass numbers or number of neutrons.
(iii) —Hydrogen, —Chlorine. —Carbon, —Oxygen.
(iv) 1 S\(^2\)2S\(^2\)2P\(^62\)3S\(^2\)3P\(^5\)
(b)(i) 1. DIFFERENCES IN PHYSICAL PROPERTIES
METALS
NON — METALS
Good conductors of heat and electricity
Poor conductors of heat and electricity
Malleable - can be beaten into thin sheets
Not malleable / brittle
Ductile — can be stretched into wire
Non ductile / biittle
Possess metallic luster
Do not possess metallic luster
Are sonorous
Not sonorous
Solid at room temperature except mercury / high melting point
Solids, liquids or gases at room temperature / low melting point
2. DIFFERENCES IN CHEMICAL PROPERTIES
METALS NON
METALS
Lose their valence electrons easily / ionize by electron loss
Gain or share valence electrons easily / ionize by electron gain
Form oxides that are basic / amphoteric
Form oxides that are acidic / neutral
Are good reducing agents
Are good oxidizing agents
Have lower electro negativities
Have higher electro negativities
Have low ionization energy
Have high ionization energy
(Some reactive metals) react with dilute acids to give off hydrogen
Do not react with dilute acids to give off hydrogen.
(ii) (l) BeO, Al\(_2\)O\(_3\), ZnO, SnO\(_2\), PbO, PbO\(_2\)
(II) LiH, NaH, KH, CaCO\(_3\) MgH\(_2\)
(III) Li\(_2\)CO\(_3\), BeCO\(_3\), MgCO\(_3\), CaCO\(_3\), ZnCO\(_3\), PbCO\(_3\)
(IV) AlCl\(_3\), MgCl\(_2\), PCl\(_3\), SiCl\(_4\), NH\(_4\)Cl
(c)(i) - form coloured compounds / ions, - exhibit variable oxidation states. - form complex compounds / ion. - have magnetic properties (paramagnetism). - have catalytic properties.
(ii) —> 1s\(^2\)2s\(^2\)2p\(^6\)3s\(^2\)3p\(^6\)3d\(^{10}\)4s\(^2\) are fully filled
(d) Mr(MgCO\(_3\)) = 24 + 12 + (16 x 3) 84
Mr(Na\(_2\)CO\(_3\)) = (23 x 2) +12 + (3 x 16) = 106
moles of MgCO\(_3\) = \(\frac{3.36}{84}\) = 0.04
moles of Na\(_2\)CO\(_3\) = moles of MgCO\(_3\) = 0.04
mass of NaCO\(_3\) = 0.04 x106 = 4.24g
OR
Mr(MgCO\(_3\)) = 24 + 12 + (1 6 x 3) 84
Mr(Na\(_2\)CO\(_3\)) = (23 x 2) +12 + (3 x 16) = 106
84g of MgCO\(_3\) produced from 10\(^6\)g Na\(_2\)CO\(_3\)
3.36g of MgCO\(_3\) will be produced
From 106 x \(\frac{3.36}{84}\) = 4.24g
Source: Myschool Past Questions Archive (Record #51011)