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Chemistry
WAEC / WASSCE 2025
Acids, Bases, and Salts
Solution
Biotechnology is applied in the following processes except
A
baking of bread
B
production of wine
C
production of antibiotics
D
manufacturing of soap
medium Difficulty
Verified Correct Answer: Option D
Chemical Principles & Mechanism
Biotechnology is defined as the use of living organisms or their components to create products or services.
Soap is traditionally made through a purely chemical process called saponification, which involves reacting fats or oils with a strong base (like sodium hydroxide). This process does not typically require the use of living cells or biological systems.
Source: Myschool Past Questions Archive (Record #77146)
Chemistry
WAEC / WASSCE 2025
Stoichiometry & Mole Concept
Solution
The percentage by mass of water in Na\(_2\)CO\(_3\).10H\(_2\)O is [ Na\(_2\)CO\(_3\).10H\(_2\)O = 286, H\(_2\)O = 18 ]
A
68.4%
B
62.9%
C
9.7%
D
6.3%
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
Given:
mass of water = 18 ; but there are 10 moles of H\(_2\)O = 10 x 18 = 180
mass of Na\(_2\)CO\(_3\).10H\(_2\)O= 286
.: Percentage by mass of water = \(\frac{mass of water}{mass of Na{_2}CO{_3}.10H{_2}O}\) x 100
= \(\frac{180}{286}\) X 100
= 62.9%
Source: Myschool Past Questions Archive (Record #77147)
Chemistry
WAEC / WASSCE 2025
Acids, Bases, and Salts
Solution
Which of the following conditions are necessary for the preparation of alkanoates from alkanols and alkanoic acids?
A
Water and NaOH
B
Conc. H\(_2\)SO\(_4\) and heat
C
NaOH and heat
D
Water and aqueous HCl
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
The chemical reaction illustrated in the question above is an esterification reaction. Esterification reaction is the reaction between an alkanol (alcohol) and an alkanoic acid (carboxylic acid) in the presence of an acid catalyst forms an ester (alkanoate) and water. To produce alkanoates (esters) from alkanols and alkanoic acids, you need to perform esterification, which requires a concentrated acid catalyst (like H\(_2\)SO\(_4\)) and heat.
Source: Myschool Past Questions Archive (Record #77148)
Chemistry
WAEC / WASSCE 2025
Atomic Structure and Periodic Table
Solution
All the following compounds are covalent except
A
NO\(_2\)
B
SO\(_3\)
C
SO\(_2\)
D
KNO\(_3\)
medium Difficulty
Verified Correct Answer: Option D
Chemical Principles & Mechanism
KNO\(_3\) (Potassium Nitrate) is primarily an ionic compound. It consists of a metal cation (K\(^+\)) and a polyatomic non-metal anion (NO\(_3\)). While covalent bonds exist within the nitrate ion itself (NO\(_3\)\(^-\)), the overall structure is held together by ionic bonds.
Source: Myschool Past Questions Archive (Record #77149)
Chemistry
WAEC / WASSCE 2025
Acids, Bases, and Salts
Solution
A salt that could be prepared by double decomposition is
A
sodium trioxocarbonate (IV)
B
barium trioxonitrate (V)
C
lead (II) trioxonitrate (V)
D
silver chloride
medium Difficulty
Verified Correct Answer: Option D
Chemical Principles & Mechanism
Double decomposition (also known as a precipitation reaction) is the standard laboratory method for preparing insoluble salts. In this process, two soluble salts are mixed in aqueous solution; their ions exchange partners to form one soluble product and one insoluble solid (precipitate).
Silver chloride (AgCl) is a highly insoluble salt. It is typically prepared by reacting two soluble solutions, such as silver nitrate (AgNO\(_3\)) and sodium chloride (NaCl).
AgNO\(_3\) + NaCl → AgCl + NaNO\(_3\)
Source: Myschool Past Questions Archive (Record #77150)
Chemistry
WAEC / WASSCE 2025
Matter & Separation Techniques
Solution
The IUPAC name of the compound CH\(_3\)CHClCH\(_2\)OH is
A
chloropropanol
B
1-chloropropan-1-ol
C
2-chloropropan-3-ol
D
2-chloropropan-1-ol
medium Difficulty
Verified Correct Answer: Option D
Chemical Principles & Mechanism
The longest carbon chain containing the principal functional group (the hydroxyl group, -OH) has three carbon atoms, giving the parent name propanol.
The chain is numbered starting from the end closest to the principal functional group (-OH) to give it the lowest possible locant. Therefore, the carbon attached to the -OH group is C1. With the -OH group at position 1, the chlorine atom (-Cl) is attached to the second carbon atom (C2).
Combining the substituent (2-chloro) with the parent chain (propan-1-ol) results in 2-chloropropan-1-ol.
Source: Myschool Past Questions Archive (Record #77151)
Chemistry
WAEC / WASSCE 2025
Atomic Structure and Periodic Table
Solution
Neutral atom of Neon with atomic number 10 is isoelectronic with
A
K\(^+\)
B
Mg\(^{2+}\)
C
Ca\(^{2+}\)
D
Li\(^+\)
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
The atomic number of Neon (Z) is 10. In a neutral atom, the number of electrons is equal to the atomic number. Therefore, Neon has 10 electrons.
Isoelectronic species are atoms or ions that have the same number of electrons. To find the correct match, calculate the number of electrons for each given ion:
K\(^+\) = A +1 charge means it has lost 1 electron. Electrons = 19 - 1 = 18 electrons
Mg\(^{2+}\) = A +2 charge means it has lost 2 electrons. Electrons = 12 - 2 = 10 electrons
Ca\(^{2+}\) = A +2 charge means it has lost 2 electrons. Electrons = 20 - 2 = 18 electrons
Li\(^+\) = A +1 charge means it has lost 1 electron. Electrons = 3 - 1 = 2 electrons
Neon has 10 electrons. Among the choices, only Mg\(^{2+}\) has 10 electrons. Hence, they are isoelectronic.
Source: Myschool Past Questions Archive (Record #77152)
Chemistry
WAEC / WASSCE 2025
Atomic Structure and Periodic Table
Solution
Which of the following species is the most powerful reducing agent?
A
Bromine atom
B
Chlorine atom
C
Fluoride atom
D
Iodine atom
medium Difficulty
Verified Correct Answer: Option D
Chemical Principles & Mechanism
A reducing agent is a species that donates electrons to another substance and is itself oxidized in the process. The strength of a reducing agent among halogens is determined by how easily it loses an electron, which depends on its atomic size (as you move down Group VII (from fluorine to iodine), the atomic radius increases), electronegativity( Iodine has the lowest electronegativity among the common halogens (F, Cl, Br, I), meaning it has the weakest pull on its outer electrons) and ionization energy( because the outer electrons in iodine are furthest from the nucleus and more shielded, it has the lowest ionization energy in this group, making it the most willing to donate an electron).
Source: Myschool Past Questions Archive (Record #77153)
Chemistry
WAEC / WASSCE 2025
Atomic Structure and Periodic Table
Solution
The electron configuration of element Y is 1S\(^2\)2S\(^2\)2P\(^6\)3S\(^2\)3P\(^4\). Y, therefore,
A
has mass number of 16
B
has three unpaired electron
C
belongs to period 4
D
belongs to group VI
medium Difficulty
Verified Correct Answer: Option D
Chemical Principles & Mechanism
The atomic number (Z) is equal to the total number of electrons in a neutral atom. By summing the exponents in the electron configuration: 2+2+6+2+4 = 16
An atomic number of 16 identifies the element as Sulphur (S). Element Y belongs to group VI because it has six electrons in its outermost shell.
Source: Myschool Past Questions Archive (Record #77154)
Chemistry
WAEC / WASSCE 2025
Atomic Structure and Periodic Table
Solution
Which of the following alkanols is tertiary?
A
2-methylpentan-2-ol
B
2-methylpentan-1-ol
C
pentan-3-ol
D
pentan-2-ol
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
A tertiary alcohol (or alkanol) is one in which the hydroxyl (-OH) group is attached to a carbon atom that is directly bonded to three other carbon atoms.
In the case of 2-methylpentan-2-ol:
The parent chain is pentane (5 carbons), the hydroxyl group is on carbon-2, a methyl branch is also on carbon-2.
Consequently, the second carbon atom is bonded to:
Carbon-1 (from the main chain)
Carbon-3 (from the main chain)
The carbon of the methyl group. However, because this central carbon is bonded to three other carbons, it is a tertiary carbon, making the molecule a tertiary alcohol.
Source: Myschool Past Questions Archive (Record #77155)
Chemistry
WAEC / WASSCE 2025
Acids, Bases, and Salts
Solution
Which of the following elements is commercially obtained by the electrolysis of its fused salt?
A
Silver
B
Copper
C
Helium
D
Sodium
medium Difficulty
Verified Correct Answer: Option D
Chemical Principles & Mechanism
Sodium is a highly reactive metal positioned high in the reactivity series. Because it is more reactive than hydrogen, it cannot be obtained by the electrolysis of its aqueous solution (brine), as water would be reduced at the cathode instead.
Commercially, sodium is produced through the Downs process, which involves the electrolysis of its fused (molten) salt, sodium chloride (NaCl).
Source: Myschool Past Questions Archive (Record #77156)
Chemistry
WAEC / WASSCE 2025
Atomic Structure and Periodic Table
Solution
The lustre of a metal is due to its
A
high density
B
refractive density
C
chemical inertness
D
free electrons
medium Difficulty
Verified Correct Answer: Option D
Chemical Principles & Mechanism
The characteristic shine or lustre of a metal is primarily caused by the presence of free (delocalized) electrons on its surface.
Light Interaction: When light strikes a metal, these mobile electrons absorb the light energy.
Reflection: The electrons oscillate and immediately re-emit the energy as light, resulting in specular reflection that gives metals their shiny appearance.
Visibility: Because metals are opaque, light cannot pass through them; it is instead reflected by this "sea of electrons" back to our eyes.
Source: Myschool Past Questions Archive (Record #77157)
Chemistry
WAEC / WASSCE 2025
Atomic Structure and Periodic Table
Solution
Exothermic reactions take place when energy given out in making bonds is
A
less than energy in for breaking bonds
B
more than energy taken in for breaking bonds
C
equal to the energy taken in for breaking bonds
D
remains the same as the energy taken in
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
Breaking chemical bonds is an endothermic process because it requires energy to be absorbed from the surroundings to overcome the attractive forces between atoms.
Bond Making (Energy Out): Forming new chemical bonds is an exothermic process because energy is released when atoms settle into a more stable, lower-energy state.
Net Result: A reaction is classified as exothermic overall if the energy released during the formation of new bonds (products) is greater than the energy required to break the original bonds (reactants). This excess energy is released to the surroundings, typically as heat.
Source: Myschool Past Questions Archive (Record #77158)
Chemistry
WAEC / WASSCE 2025
Acids, Bases, and Salts
Solution
Which of the following metals would not release hydrogen when reacted with dilute HCl?
A
Calcium
B
Silver
C
Iron
D
Zinc
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
Silver (Ag) is located below hydrogen in the reactivity series. For a metal to release hydrogen gas when reacted with a dilute acid like HCl, it must be more reactive than hydrogen to displace it from the acid. Because silver is less reactive, it cannot displace hydrogen ions (H\(^+\)) to form hydrogen gas (H\(_2\)), and thus no reaction occurs.
Source: Myschool Past Questions Archive (Record #77159)
Chemistry
WAEC / WASSCE 2025
Atomic Structure and Periodic Table
Solution
Five d-orbitals have the same energy level in an isolated transition metal are described as
A
degenerate
B
non-degenerate
C
high level orbital
D
low-level orbital
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
In gaseous ion (one not bonded to any ligands) or an isolated transition metal atom, all five d-orbitals (d\(_{xy}\), d\(_{yz}\), d\(_{xz}\),...) possess the exact same energy level. In quantum chemistry, orbitals that share the same energy are formally defined as degenerate. This symmetry exists because there is no external electric or magnetic field (such as that from approaching ligands) to distinguish the orbitals' orientations relative to one another.
Source: Myschool Past Questions Archive (Record #77160)