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Chemistry
WAEC / WASSCE 2018
Stoichiometry, Mole Concept & Volumetric Analysis
Solution
Which of the following CANNOT be an empirical formula?
A
\(CH\)
B
\(CH_{2}\)
C
\(P_{2}O_{5}\)
D
\(N_{2}O_{4}\)
medium Difficulty
Verified Correct Answer: Option D
Chemical Principles & Mechanism
The empirical formula is always in the ratio of the smallest positive integer, hence, \(N_{2}O_{4}\) has an empirical formula \(NO_{2}\).
Source: Myschool Past Questions Archive (Record #49079)
Chemistry
WAEC / WASSCE 2018
Organic Chemistry I: Hydrocarbons & Crude Oil
Solution
One of the criteria for confirming the purity of benzene is to determine its
A
heat capacity
B
boiling point
C
mass
D
colour
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
Any pure substance will have a specific melting and boiling point. The presence of impurities alters the boiling point of benzene.
Source: Myschool Past Questions Archive (Record #49081)
Chemistry
WAEC / WASSCE 2018
Acids, Bases, pH & Salts
Solution
When chlorine is passed through a sample of water, the pH of the water sample would be
A
< 7
B
> 7
C
= 7
D
0
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
\(Cl_{2} + H_{2}O \to HCl + HOCl\)
The two compounds in the product end are acidic and hence, their mixture is acidic. Hence, the pH is < 7
Source: Myschool Past Questions Archive (Record #49082)
Chemistry
WAEC / WASSCE 2018
Stoichiometry, Mole Concept & Volumetric Analysis
Solution
How many atoms are contained in 0.2moles of nitrogen? \([N_{A} = 6.02 \times 10^{23}]\)
A
\(1.20 \times 10^{23}\)
B
\(2.41 \times 10^{23}\)
C
\(3.62 \times 10^{23}\)
D
\(4.82 \times 10^{23}\)
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
\(1 mole = 6.02 \times 10^{23} atoms\)
\(0.2 moles = 6.02 \times 10^{23} \times 0.2\) atoms
= \(1.204 \times 10^{23}\)
\(\approxeq 1.2 \times 10^{23}\)
Source: Myschool Past Questions Archive (Record #49083)
Chemistry
WAEC / WASSCE 2018
Chemical Bonding & Intermolecular Forces
Solution
The strength of metallic bonds depends on the
A
charge density of the atoms
B
ductility of the metal
C
number of valence electrons
D
total number of electrons in the atom
medium Difficulty
Verified Correct Answer: Option C
Chemical Principles & Mechanism
It is determined by the difference in the electron structures of the atoms. These primarily are: The number of outer electrons, i.e the number of valence shell electrons released during a metallic bond.
Source: Myschool Past Questions Archive (Record #49085)
Chemistry
WAEC / WASSCE 2018
Oxidation, Reduction & Redox Reactions
Solution
When zinc is added to AgN\(O_3\) solution, crystals of silver forms on the zinc surface. This indicates that zinc is
A
oxidised
B
reduced
C
decomposed
D
dissociated
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
Reaction: \(2AgNO_{3} + Zn \to Zn(NO_{3})_{2} + 2Ag\)
The oxidation number of Zn in the reactant is 0, and in the product is +2. Therefor, it is oxidized.
Source: Myschool Past Questions Archive (Record #49087)
Chemistry
WAEC / WASSCE 2018
Stoichiometry, Mole Concept & Volumetric Analysis
Solution
The empirical formula of a compound containing 0.067mol Cu and 0.066mol O is [Cu = 63.5, O = 16]
A
\(Cu_{2}O\)
B
\(CuO\)
C
\(CuO_{2}\)
D
\(CuO_{4}\)
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
Cu : O
0.067 : 0.066
mole ratio \(\frac{0.067}{0.066}\) : \(\frac{0.066}{0.066}\)
= 1 : 1
= CuO
Source: Myschool Past Questions Archive (Record #49090)
Chemistry
WAEC / WASSCE 2018
Oxidation, Reduction & Redox Reactions
Solution
The change in the oxidation state of iron in the reaction represented by the equation: \(2FeCl_{3} + H_{2}S \to 2FeCl_{2} + 2HCl + S\) is
A
+2 to +3
B
0 to +2
C
+3 to +2
D
+3 to 0
medium Difficulty
Verified Correct Answer: Option C
Chemical Principles & Mechanism
The oxidation number of Iron in \(FeCl_{3}\) = +3. The oxidation number in \(FeCl_{2}\) = +2.
Source: Myschool Past Questions Archive (Record #49095)
Chemistry
WAEC / WASSCE 2018
Nature of Matter & Separation Techniques
Which of the following methods can be used to seperate blood cells from plasma?
A
Centrifugation
B
Filtration
C
Chromatography
D
Distillation
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 #49101)
Chemistry
WAEC / WASSCE 2018
Periodic Table & Periodicity
Which of the following statements is true about ionic radius? Ionic radius
A
increases as nuclear charge increases
B
decreases as nuclear charge increases
C
decreases as nuclear charge decreases
D
remains constant as nuclear charge increases
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 #49108)
Chemistry
WAEC / WASSCE 2018
Stoichiometry, Mole Concept & Volumetric Analysis
Solution
Analysis of a hydrocarbon shows that it contains 0.93g of Carbon per gram of the compound. The mole ratio of carbon to hydrogen in the compound is [H = 1.0, C=12.0]
A
1:1
B
1:2
C
2:1
D
2:3
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
1g of Hydrocarbon = 0.93g of Carbon, therefore, Hydrogen = (1 - 0.93)g = 0.07g
C : H
0.93 : 0.07
\(\frac{0.93}{12}\) : \(\frac{0.07}{1}\)
0.078 : 0.07
\(\frac{0.078}{0.07} : \frac{0.07}{0.07}\)
\(\approxeq 1:1\)
Source: Myschool Past Questions Archive (Record #49115)
Chemistry
WAEC / WASSCE 2018
Particulate Nature of Matter, Laws & Formulae
Solution
The law of definite proportions states that
A
pure samples of the same compound contain the same elements combined in the same proportion by mass
B
pure samples of substances are in the same proportion by mass
C
chemical compounds are pure because they contain the same elements
D
matter can neither be created nor destroyed.
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
The Law of Definite Proportions states that all pure samples of a particular chemical compound contain similar elements combined in the same proportion by mass.
Source: Myschool Past Questions Archive (Record #49117)
Chemistry
WAEC / WASSCE 2018
Stoichiometry, Mole Concept & Volumetric Analysis
Solution
What is the relative molecular mass of a compound which has empirical formula \(CH_{2}O\)? [C= 12, H= 1, O= 16]
A
42
B
45
C
126
D
180
medium Difficulty
Verified Correct Answer: Option D
Chemical Principles & Mechanism
Molecular formula = (empirical formula x n)
where n= (1,2,3,...)
\(CH_{2}O = 12 + (2\times 1) + 16 = 30\)
Relative molecular mass = (30 x n)
From the options, only 180 is a multiple of 30, when n=6.
Source: Myschool Past Questions Archive (Record #49121)
Chemistry
WAEC / WASSCE 2018
Atomic Structure, Orbitals & Nuclear Chemistry
Solution
Atoms are electrically neutral because they
A
do not conduct electricity
B
contain equal number of protons and electrons
C
are composed of neutrons and electrons
D
cannot be attracted by electromagnetic field.
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
Atoms are electrically neutral because they contain equal amount of positive and negative charge. This is because they have equal number of protons and electrons.
Source: Myschool Past Questions Archive (Record #49124)
Chemistry
WAEC / WASSCE 2018
Water, Solutions & Solubility
Common Salt (NaCl) is used to preserve foods. Which of the following properties can be used to determine its purity before use?
A
Solubility in water
B
Melting point
C
Relative density
D
Crystalline nature
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 #49127)