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Chemistry
WAEC / WASSCE 2023
Acids, Bases, and Salts
Solution
Which of the elements in the table below would react more readily with chlorine?
Element
Ionization energy (KJ \(mol^{-1} \times 10^{-3}\))
W
12.0
X
21.0
Y
106.0
Z
200.0
A
Y and Z only
B
X and Z only
C
W and X only
D
W and Z only
medium Difficulty
Verified Correct Answer: Option C
Chemical Principles & Mechanism
Among the given elements, W has the lowest ionization energy (\(12.0 KJ mol^{-1} x 10^{-3})\), indicating that it would be more likely to react with chlorine. X has a higher ionization energy \((21.0 KJ mol^{-1} x 10^{-3})\), so it would be less reactive with chlorine compared to W.
Based on ionization energy values, the elements that would react more readily with chlorine are W and X.
Source: Myschool Past Questions Archive (Record #69501)
Chemistry
UTME / JAMB 2023
Matter & Separation Techniques
Solution
Which of the following statements is true for strong electrolytes?
A
They do not conduct electricity in the molten state
B
They completely dissociate into ions in solution
C
They are non-polar substances
D
They partially dissociate into ions in solution
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
They completely dissociate into ions in solution. Strong electrolytes are substances that fully dissociate into ions when dissolved in water or melted. As a result, they produce a high concentration of ions in the solution, allowing for efficient electrical conductivity.
Source: Myschool Past Questions Archive (Record #67540)
Chemistry
UTME / JAMB 2023
Atomic Structure and Periodic Table
Solution
What is the maximum number of electrons that can occupy the second energy level (n=2)?
A
2 electrons
B
18 electrons
C
8 electrons
D
32 electrons
medium Difficulty
Verified Correct Answer: Option C
Chemical Principles & Mechanism
The correct answer is (b). The second energy level (n=2) can hold a maximum of 8 electrons. It consists of two subshells, 2s and 2p, which can hold 2 and 6 electrons, respectively.
Source: Myschool Past Questions Archive (Record #67542)
Chemistry
UTME / JAMB 2023
Acids, Bases, and Salts
Solution
Which of the following is a common laboratory indicator for bases?
A
Methyl orange
B
Phenolphthalein
C
Bromothymol blue
D
Litmus
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
Phenolphthalein is a common laboratory indicator used to detect the presence of bases in a solution. In its basic form (pH > 8.3), it turns pink or purple, indicating the presence of a base.
Source: Myschool Past Questions Archive (Record #67544)
Chemistry
WAEC / WASSCE 2023
Stoichiometry & Mole Concept
Solution
The vapour density of an organic compound with the molecular formula \(C_2H_4O_2\), is
[H=1.0, C=12.0, O= 16.0]
A
40
B
120
C
65
D
30
medium Difficulty
Verified Correct Answer: Option D
Chemical Principles & Mechanism
Molar mass of \(C_2H_4O_2\),= (12 \times 2) + (1 \times 4) + (16 \times 2)= 60 g/mol
Vapour density = RMM/2
=60/2=30
Source: Myschool Past Questions Archive (Record #69495)
Chemistry
WAEC / WASSCE 2023
Stoichiometry & Mole Concept
Solution
The following statements are correct except
A
energy is released when liquids change to solids.
B
carbon atoms in gaseous methane are further apart than those in solid diamond.
C
there is large decrease in the volume of a solid metal when pressure is applied to it.
D
particles move faster in the gaseous state than in the liquid state.
medium Difficulty
Verified Correct Answer: Option C
Chemical Principles & Mechanism
In general, solids are relatively incompressible compared to liquids and gases. When pressure is applied to a solid, there is typically only a small change in volume. Solids have tightly packed particles with strong intermolecular forces, making them less responsive to changes in pressure. Liquids and gases, on the other hand, can undergo larger volume changes in response to pressure.
Source: Myschool Past Questions Archive (Record #69496)
Chemistry
WAEC / WASSCE 2023
Atomic Structure and Periodic Table
Solution
Which of the following properties does not give evidence of the kinetic theory of matter?
A
Diffusion
B
Melting
C
Polymerization
D
Evaporation
medium Difficulty
Verified Correct Answer: Option C
Chemical Principles & Mechanism
Polymerization is a process in which small molecules combine to form larger molecules. This process is not consistent with the kinetic theory of matter because it does not involve the movement of particles. The particles in a polymer are not moving randomly. They are bonded together in a fixed structure.
Therefore, the property that does not give evidence of the kinetic theory of matter is polymerization.
Source: Myschool Past Questions Archive (Record #69502)
Chemistry
WAEC / WASSCE 2023
Atomic Structure and Periodic Table
Solution
Dilute trioxonitrate (V) acid does not produce hydrogen when it reacts with metals because
A
it reacts with the product.
B
it is highly corrosive.
C
there is no visible reaction.
D
it is a strong oxidizing agent.
medium Difficulty
Verified Correct Answer: Option D
Chemical Principles & Mechanism
Dilute trioxonitrate (V) acid does not produce hydrogen when it reacts with metals because it is a strong oxidizing agent.
Trioxonitrate (V) acid, also known as nitric acid, is a strong oxidizing agent. This means that it can easily oxidize metals, which means that it can remove electrons from metals. When nitric acid oxidizes a metal, it forms salt and water. The salt does not contain hydrogen, so no hydrogen gas is produced
Source: Myschool Past Questions Archive (Record #69503)
Chemistry
WAEC / WASSCE 2023
Organic Chemistry
Solution
Which of the following statements is correct?
A
Addition reactions occur between alkanes and chlorine.
B
Butane has a lower boiling point than propane.
C
Pentane has five isomers.
D
An alkane with 49 carbon atoms contains 100 hydrogen atoms
medium Difficulty
Verified Correct Answer: Option D
Chemical Principles & Mechanism
The general formula for alkanes is \(C_nH_{2n}+2\). For an alkane with 49 carbon atoms (n = 49), the number of hydrogen atoms can be calculated as follows:
Number of hydrogen atoms (H) = 2n + 2
Number of hydrogen atoms (H) = 2 * 49 + 2
Number of hydrogen atoms (H) = 98 + 2
Number of hydrogen atoms (H) = 100
So, an alkane with 49 carbon atoms contains 100 hydrogen atoms.
Source: Myschool Past Questions Archive (Record #69504)
Chemistry
WAEC / WASSCE 2023
Matter & Separation Techniques
Solution
A mixture containing two salts of different solubility can be separated by
A
chromatography.
B
crystallization.
C
distillation.
D
evaporation.
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
Crystallization is a separation technique that exploits differences in the solubilities of components in a solution. When a solution is allowed to cool or evaporate under controlled conditions, one of the salts may begin to crystallize out of the solution before the other due to its lower solubility. This process can be used to separate the salts based on their differing solubilities and crystal formation.
Source: Myschool Past Questions Archive (Record #69505)
Chemistry
WAEC / WASSCE 2023
Matter & Separation Techniques
Solution
Species that occur in a reaction pathway but not in the overall reaction are known as
A
Reactants
B
Inhibitors
C
Products
D
Intermediates
medium Difficulty
Verified Correct Answer: Option D
Chemical Principles & Mechanism
In a chemical reaction, intermediates are the chemical species that are formed during the reaction but are subsequently consumed in further steps, leading to the final products. They are transient species that exist momentarily during the reaction process and are not present in the initial reactants or the final products of the overall reaction.
Source: Myschool Past Questions Archive (Record #69506)
Chemistry
WAEC / WASSCE 2023
Stoichiometry & Mole Concept
Solution
How many moles are there in 3.0 g of \(O_2\)? [O = 16.0]
A
0.0093 moles.
B
0.0930 moles.
C
0.0625 moles.
D
0.6250 moles.
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
Number of moles = Mass / Molar mass
Given that the molar mass of oxygen \(O_2\) is 32.0 g/mol (2 \times 16.0 g/mol), you can calculate the number of moles:
Number of moles = 3.0 g / 32.0 g/mol = 0.09375 moles
Rounded to four significant figures, the number of moles in 3.0 g of O2 is approximately 0.0938 moles.
Therefore, the closest answer choice is:
0.0930 moles.
Source: Myschool Past Questions Archive (Record #69507)
Chemistry
WAEC / WASSCE 2023
Stoichiometry & Mole Concept
Solution
Which of the following equimolar solutions has the highest conductivity?
A
\(H_2SO{_4(aq)}\)
B
\(NaOH{_(aq)}\)
C
\(H_2CO{_3(aq)}\)
D
\(CH_3COOH{_4(aq)}\)
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
\(H_2SO_4\)(aq) is a strong acid that dissociates into two hydrogen ions (H+) and one sulfate ion \(SO4^{2-}\) when dissolved in water. This leads to a higher concentration of ions in the solution, resulting in higher conductivity.
Source: Myschool Past Questions Archive (Record #69508)
Chemistry
WAEC / WASSCE 2023
Organic Chemistry
Solution
The pair of compounds that belongs to the same homologous series is
A
\(C_2H_6\) and \(C_4H_{10}\)
B
\(C_3H_8\) and \(C_3H_6\)
C
\(C_2H_4\) and \(C_4H_{10}\)
D
\(C_4H_{10}\) and \(C_5H_{10}\)
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
In the given options, \(C_2H_6\) (ethane) and \(C_4H_{10}\) (butane) both belong to the same homologous series, as they have the same alkane functional group \(C_nH_{2n}+2\) and differ by a \(CH_2\) group:
\(C_2H_6\): Ethane
\(C_4H_{10}\): Butane
Both of these compounds are members of the alkane homologous series.
Source: Myschool Past Questions Archive (Record #69509)
Chemistry
WAEC / WASSCE 2023
Matter & Separation Techniques
Solution
Which of the following equations does not illustrate correctly one of the reactions of chlorine?
A
\(Ca(OH)_2 + Cl_2 → CaOCl_2 + H_2O\)
B
\(Cl_2 + 2NaF → 2NaCl + F_2\)
C
\(Cl_2 + 2NaOH → NaCl + NaClO + H_2O\)
D
\(H_2S + Cl_2 → 2HCl + S\)
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
The equation \(Cl_2 + 2NaF → 2NaCl + F_2\) does not illustrate correctly one of the reactions of chlorine.
In this reaction, chlorine reacts with sodium fluoride to form sodium chloride and fluorine gas. However, this reaction is not possible because fluorine is a much more reactive element than chlorine. When chlorine and fluorine react, they form a compound called chlorine trifluoride (\(ClF_3)\), which is a very powerful oxidizing agent.
Source: Myschool Past Questions Archive (Record #69510)