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Chemistry
WAEC / WASSCE 2017
Stoichiometry, Mole Concept & Volumetric Analysis
Solution
The number of atoms present in 2.5moles of a triatomic gas is equivalent to [1mole = \(6.02\times 10^{23}\)]
A
\(2.5\times 10^{23}\)
B
\(1.5\times 10^{23}\)
C
\(1.5\times 10^{24}\)
D
\(2.5\times 10^{24}\)
medium Difficulty
Verified Correct Answer: Option C
Chemical Principles & Mechanism
1 mole = \(6.02 \times 10^{23}\)
2.5 moles = \(6.02 \times 10^{23} \times 2.5\)
= \(15.05 \times 10^{23} = 1.505 \times 10^{24}\)
\(\approxeq 1.5 \times 10^{24}\)
Source: Myschool Past Questions Archive (Record #49274)
Chemistry
WAEC / WASSCE 2017
Chemical Energetics & Thermochemistry
Solution
When Magnesium reacts with oxygen, heat is
A
absorbed and the reaction is endothermic
B
evolved and the reaction is endothermic
C
evolved and the reaction is exothermic
D
absorbed and the reaction is exothermic
medium Difficulty
Verified Correct Answer: Option C
Chemical Principles & Mechanism
The Magnesium actually reacts with oxygen in the air, is burnt and produces a bright light. The bright light emits a lot of heat so the reaction is exothermic.
Source: Myschool Past Questions Archive (Record #49275)
Chemistry
WAEC / WASSCE 2017
Stoichiometry, Mole Concept & Volumetric Analysis
Solution
Which of the following gases is not acidic?
A
\(SO_{3}\)
B
\(NO_{2}\)
C
\(Co_{2}\)
D
CO
medium Difficulty
Verified Correct Answer: Option D
Chemical Principles & Mechanism
The compound CO is treated as a neutral oxide, though in truth, it is slightly acidic. Regardless of this, within the options supplied, CO is the best option available.
Source: Myschool Past Questions Archive (Record #49276)
Chemistry
WAEC / WASSCE 2017
Stoichiometry, Mole Concept & Volumetric Analysis
Solution
A hydrocarbon contained 14.3% hydrogen. The empirical formula for the hydrocarbon is [H= 1.0, C= 12.0]
A
\(CH\)
B
\(CH_{2}\)
C
\(CH_{3}\)
D
\(CH_{4}\)
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
The percentage of Carbon in the compound is (100 - 14.3)% = 85.7%
C : H
\(\frac{85.7}{12.0} : \frac{14.3}{1.0}\)
\( 7.14 : 14.3\)
\(\frac{7.14}{7.14} : \frac{14.3}{7.14}\)
\(\approxeq 1 : 2\)
Therefore, the empirical formula is \(CH_{2}\).
Source: Myschool Past Questions Archive (Record #49291)
Chemistry
WAEC / WASSCE 2017
Stoichiometry, Mole Concept & Volumetric Analysis
Solution
Which of the following statements is NOT a chemical property of an acid?
A
Evolution of ammonia when heated with ammonium salts
B
Evolution of carbon dioxide gas when added to a trioxocarbonate (IV) salt
C
Formation of salt and water with alkalis
D
Formation of salt and hydrogen gas with reactive metals
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
Ammonium salts react with bases to release ammonia and not with acids.
Source: Myschool Past Questions Archive (Record #49295)
Chemistry
WAEC / WASSCE 2017
Stoichiometry, Mole Concept & Volumetric Analysis
Solution
Halogens generally react with metals to form
A
alkalis
B
acids
C
bases
D
salts
medium Difficulty
Verified Correct Answer: Option D
Chemical Principles & Mechanism
The word "halogen" is a Greek word meaning salt former, because they form salts when they react with metals eg NaCl.
Source: Myschool Past Questions Archive (Record #49302)
Chemistry
WAEC / WASSCE 2017
Chemical Bonding & Intermolecular Forces
Solution
Potassium Chloride solid does not conduct electricity because
A
it is a covalent compound
B
strong cohesive forces make its ions immobile
C
strong cohesive force makes its molecule immobile
D
each of potassium and chlorine structures contain noble gas structure
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
For a substance to conduct electricity, it must have charge particles like electrons and ions within it that are able to move freely throughout it. In its solid state, potassium chloride (like many other ionic compounds) have fixed ions, hence, they are immobile and can't conduct electricity.
Source: Myschool Past Questions Archive (Record #49305)
Chemistry
WAEC / WASSCE 2017
Stoichiometry, Mole Concept & Volumetric Analysis
Solution
When water was added to a white anhydrous substance X, the colour changed to blue. X is
A
\(CuSO_{4}\)
B
\(FeSO_{4}\)
C
\(Na_{2}SO_{4}\)
D
\(PbSO_{4}\)
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
When water is added to white coloured anhydrous copper sulphate, its colour changes to blue, indicating that the blue coloured copper sulphate pentahydrate is regenerated.
Source: Myschool Past Questions Archive (Record #49311)
Chemistry
WAEC / WASSCE 2017
Water, Solutions & Solubility
Solubility curve can be used in the determination of the
A
amount of crystals formed
B
amount of solvent that can be recovered
C
amount of solid drugs in a given solution
D
temperature of the solution
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 #49312)
Chemistry
WAEC / WASSCE 2017
Water, Solutions & Solubility
Solution
If 0.2g of a salt is required to saturate 200\(cm^{3}\) of water at room temperature, what is the solubility of the salt?
A
0.2\(gdm^{-3}\)
B
1.0\(gdm^{-3}\)
C
2.0\(gdm^{-3}\)
D
5.0\(gdm^{-3}\)
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
Solubility in \(gdm^{-3}\) = \(\frac{mass of salt in gram}{volume of liquid in dm^{3}}\)
200\(cm^{3}\) = \(\frac{200}{1000} dm^{3} = 0.2dm^{3}\)
Solubility = \(\frac{0.2g}{0.2dm^{3}}\)
= 1.0\(gdm^{-3}\)
Source: Myschool Past Questions Archive (Record #49313)
Chemistry
WAEC / WASSCE 2017
Reaction Rates & Chemical Equilibrium
Solution
The property of a chemical reaction that is affected by the presence of a catalyst is
A
activation energy
B
free energy
C
equilibrium position
D
enthalpy change
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
The activation energy is the amount of energy that is required to form products in a reaction. The presence of a catalyst helps to speed up the reaction such that the energy needed for the reaction is reduced.
Source: Myschool Past Questions Archive (Record #49315)
Chemistry
WAEC / WASSCE 2017
Acids, Bases, pH & Salts
Solution
Soluble salts can be prepared by the following methods except
A
neutralization
B
reaction of an acid with trioxocarbonate(IV) salt
C
double decomposition
D
reaction of an acid with electropositive metals
medium Difficulty
Verified Correct Answer: Option C
Chemical Principles & Mechanism
Soluble salts cannot be produced by double decomposition( precipitation of an insoluble salt)
Source: Myschool Past Questions Archive (Record #49318)
Chemistry
WAEC / WASSCE 2017
Reaction Rates & Chemical Equilibrium
Solution
Chemical reactions occurs when the colliding reactants have energy that is
A
less than the activation energy
B
greater than the activation energy
C
greater than the energy of the product
D
less than the energy of effective collision
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
The energy of the reactants must be more than the activation energy in order for product to be formed.
Source: Myschool Past Questions Archive (Record #49320)
Chemistry
WAEC / WASSCE 2017
Electrolysis & Electrochemical Cells
Solution
The common feature of reactions at the anode is that
A
electrons are consumed
B
ions are reduced
C
oxidation is involved
D
the electrode dissolves
medium Difficulty
Verified Correct Answer: Option C
Chemical Principles & Mechanism
In both the electrochemical cell and the electrolytic cell, at the anode, oxidation is involved.
Source: Myschool Past Questions Archive (Record #49323)
Chemistry
WAEC / WASSCE 2017
Oxidation, Reduction & Redox Reactions
Solution
Consider the following reaction equation: \(2NO_{(g)} + O_{{2}{(g)}} \to 2NO_{{2}{(g)}}\). What is the change in the oxidation number of nitrogen?
A
+2 to 0
B
+2 to -2
C
+2 to +4
D
+4 to +2
medium Difficulty
Verified Correct Answer: Option C
Chemical Principles & Mechanism
In NO, the oxidation number for nitrogen is N - 2 = 0
⇒ N = +2
In \(NO_{2}\), we have N - (2x2) =0
N - 4 =0
N =+4
Source: Myschool Past Questions Archive (Record #49324)