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Chemistry
WAEC / WASSCE 2002
Stoichiometry, Mole Concept & Volumetric Analysis
Solution
Equal amounts of marble chips are reacted separately with 100cm3 of hydrochloric acid of different concentrations. If all the marble chips reacted; which of the following remained the same in each case?
A
Average rate of evoluton of gas
B
Total mass of gas evolved during the reaction
C
Time taken for the reaction to reach completion
D
Initial reaction rates
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
The total mass of gas evolved during the reaction will remain the same in each case. This is because the amount of marble chips is the same in each case, and the reaction goes to completion. Therefore, the same amount of gas will be produced in each case, regardless of the concentration of the hydrochloric acid.
Source: Myschool Past Questions Archive (Record #40025)
Chemistry
WAEC / WASSCE 2002
Nature of Matter & Separation Techniques
CuSO45H2O can be obtained from an aqueous solution of copper (ll) tetraoxosulphate (VI) by
A
evaporation to dryness
B
using chromatography
C
precipitation
D
crystallization
medium Difficulty
Verified Correct Answer: Option D
Chemical Principles & Mechanism
No expanded working has been attached for this question yet. The verified answer is Option D.
Source: Myschool Past Questions Archive (Record #40026)
Chemistry
WAEC / WASSCE 2002
Nature of Matter & Separation Techniques
Which of the following compounds will leave a metal residue when heated?
A
Cu(NO3)2
B
AgNO3
C
K2CO3
D
CaCO3
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 #40027)
Chemistry
WAEC / WASSCE 2002
Stoichiometry, Mole Concept & Volumetric Analysis
A visible change is observed when a strip of iron is placed in an aqueous solution of
A
FeSO4
B
ZnSO4
C
CuSO4
D
MgSO4
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 #40032)
Chemistry
WAEC / WASSCE 2002
Oxidation, Reduction & Redox Reactions
Solution
Consider the following equation: Cr\(_2\)O\(_7\)\(^{2-}\)(aq) + 14H\(^+\)(aq) + 6e\(^-\) → 2Cr\(^{3+}\)(ag) + 7H\(_2\)O(1). The oxidation number of chromium changes from
A
-2 to + 3
B
-2 to + 6
C
+6 to +3
D
+7 to + 6
medium Difficulty
Verified Correct Answer: Option C
Chemical Principles & Mechanism
Cr\(_2\)O\(_7\)\(^{2-}\)(aq) + 14H\(^+\)(aq) + 6e\(^-\) → 2Cr\(^{3+}\)(ag) + 7H\(_2\)O(1).
All we need to do is to calculate the oxidation number of Cr on the reactant side (LHS) and compare with the one on the RHS.
Cr\(_2\)O\(_7\)\(^{2-}\) → Cr\(^{3+}\)
Cr\(_2\)O\(_7\) = - 2 → Cr = + 3
2Cr + 7(O) = - 2
2Cr + 7(- 2) = - 2
2Cr - 14 = - 2
2Cr = - 2 + 14
2Cr = + 12
Cr = \(\frac{12}{2}\)
Cr = + 6 → Cr = + 3
Therefore, the change in oxidation number of Cr changed from +6 to +3 - Option C
Source: Myschool Past Questions Archive (Record #40034)
Chemistry
WAEC / WASSCE 2002
Electrolysis & Electrochemical Cells
Solution
When concentrated sodium chloride solution is electrolysed using inert electrodes, the products are
A
oxygen and hydrogen
B
hydrogen and chlorine
C
sodium and oxygen
D
sodium and chlorine
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
When a concentrated solution of sodium chloride (also known as brine) is electrolyzed using inert electrodes (such as graphite or platinum), the ions present in the solution are Na\(^+\), Cl\(^-\), H\(^+\) and OH\(^-\). The products are determined by the preferential discharge of these ions:
At the Cathode (Negative Electrode): Both Na\(^+\) and H\(^+\) ions migrate to the cathode. H\(^+\) ions are lower in the electrochemical series (more easily reduced) than Na\(^+\) ,so hydrogen gas (H\(^+\)) is liberated.
At the Anode (Positive Electrode): Both OH\(^-\) and Cl\(^-\)ions migrate to the anode. Although OH\(^-\) is normally easier to discharge, the high concentration of chloride ions causes Cl\(^-\) to be preferentially discharged, resulting in the evolution of chlorine gas Cl\(_2\).
In Solution: The remaining Na\(^+\) and OH\(^-\) ions combine to form sodium hydroxide (NaOH).
Source: Myschool Past Questions Archive (Record #40037)
Chemistry
WAEC / WASSCE 2002
Stoichiometry, Mole Concept & Volumetric Analysis
When alkynes are hydrogenated completely they produce compounds with the general molecular formula
A
CnHn
B
CnH2n
C
CnH2n+2
D
CnH2n-2
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 #40040)
Chemistry
WAEC / WASSCE 2002
Organic Chemistry I: Hydrocarbons & Crude Oil
The reaction between ethene and chlorine to form 1, 2-dichloroethane is
A
oxidation
B
polymerization
C
addition
D
substitution
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 #40042)
Chemistry
WAEC / WASSCE 2002
Organic Chemistry II: Functional Groups, Polymers & Biomolecules
Solution
Which of the following types of alkanols undergo oxidation to produce alkanoic acids? I. Primary alkanols II. Secondary alkanols III. Tertiary alkanols
A
I,II and III
B
l and ll only
C
ll only
D
l only
medium Difficulty
Verified Correct Answer: Option D
Chemical Principles & Mechanism
Primary alkanols undergo oxidation to yield Alkanoic acid or Aldehyde depending on the conditions.
Secondary alkanols undergo oxidation to yield Ketones, while
Tertiary alkanols do not mostly undergo oxidation.
Source: Myschool Past Questions Archive (Record #40044)
Chemistry
WAEC / WASSCE 2002
Organic Chemistry II: Functional Groups, Polymers & Biomolecules
A suitable reagent for distinguishing between ethanoic acid ethanol is
A
bromine water
B
Fehling's solution
C
sodium hydrogentrioxocarbonate (IV)
D
ammoniacal silver trioxonitrate (V)
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 #40045)
Chemistry
WAEC / WASSCE 2002
Organic Chemistry II: Functional Groups, Polymers & Biomolecules
The reaction of sucrose with dilute HCI produces
A
an alkanoate
B
glucose and fructose
C
a black mass of carbon
D
a polysaccharide
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 #40046)
Chemistry
WAEC / WASSCE 2002
Stoichiometry, Mole Concept & Volumetric Analysis
Solution
The energy value of petrol can be determined by a
A
bomb calorimeter
B
catalytic cracker
C
fractionating column
D
thermometer
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
A bomb calorimeter is a specialized device used to measure the calorific value (energy content) of a substance, such as petrol. It works by burning a known mass of the fuel in a pressurized, oxygen-rich environment (the "bomb"). The heat released during this combustion is absorbed by a surrounding water bath, and the resulting temperature rise is used to calculate the total energy content of the fuel in Joules or calories.
Source: Myschool Past Questions Archive (Record #40047)
Chemistry
WAEC / WASSCE 2002
Metals, Transition Elements & Extraction
Iron is often galvanized in order to
A
make it more malleable
B
remove the impurities in it
C
protect it against corrosion
D
render it passive
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 #40048)
Chemistry
WAEC / WASSCE 2002
Stoichiometry, Mole Concept & Volumetric Analysis
One of the methods used for combating air pollution is
A
burning of solid waste
B
provision of sanitary land fills
C
legislation against some industrial practices
D
scavenging of refuse dumps
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 #40049)
Chemistry
WAEC / WASSCE 2002
Acids, Bases, pH & Salts
Solution
(a) Suggest how the following liquid reagents can be suitably stored in the laboratory
(i) X which fumes in moist air;
(ii) Y which is slowly decomposed by sunlight in ordinary reagent bottles.
(b) State what is observed when aqueous ammonia is added to:
(i) litmus paper;
(ii) Pb(NO\(_3\))\(_2\) solution in drops until in excess
(iii) freshly precipitated AgCI in excess.
(c) A salt sample was suspected to be either Na\(_2\)CO\(_2\) or NaHCO\(_3\). A student who was required to identify it tested a portion for solubility in water and then for effect on litmus paper.
(i) What was observed in each case?
(ii) Give the reason why the student's procedure was unsuitable
(iii) Describe briefly how you would have identified the salt.
A
burning of solid waste
B
provision of sanitary land fills
C
legislation against some industrial practices
D
scavenging of refuse dumps
medium Difficulty
Verified Correct Answer: Option C
Chemical Principles & Mechanism
(a)(i) X is better stored in fume cupboard/chamber
(ii) Y should be stored in coloured bottles or dark cupboard
(b)(i) it turns red litmus paper to blue, but no action on blue litmus paper.
(ii) A white gelatinous precipitate is formed and it will be insoluble in ammonium solution.
(iii) A white freshly precipitate of the freshly prepared of AgCl will dissolve.
(c)(i) Na\(_2\)CO\(_3\) is neutral to litmus but NaHCO\(_{3(aq)}\) Will turn blue litmus to red.
(ii) The procedure was not suitable because the two substances are soluble in water and hence they cannot be detected using solubility.
(iii) Na\(_2\)CO\(_3\) and NaHCO\(_3\) should be separately heated strongly. NaCO\(_3\) is stable under heat but NaHCO\(_3\) vill decompose given off H\(_2\)O and CO\(_2\) and leaving Na\(_2\)CO\(_3\). The water and CO\(_2\) can be tested to confirm which is which.
Source: Official Exam / Past Question Archive