2025 WAEC GCE FIRST Series Chemistry Questions and Answers

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 2025 WAEC GCE 1st Series Chemistry Theory Questions and Answers Expo Runz

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(1a)
(1) Al(NO₃)₃: Aluminum nitrate
(2) HClO₃: Chloric acid

(1b)
Given:
– Mass of Na₃PO₄ = 355 g
– Volume of solution = 3.5 dm³
– Molar mass of Na₃PO₄ = (23.0 × 3) + 31.0 + (16.0 × 4) = 69 + 31 + 64 = 164 g/mol

Number of moles of Na₃PO₄ = Mass / Molar mass = 355 / 164 = 2.16 mol

Concentration (mol/dm³) = Moles / Volume = 2.16 / 3.5 = 0.617 mol/dm³

(1c)
Ionization energy is the minimum energy required to remove the most loosely bound electron from an isolated gaseous atom in its ground state.

(1d)
Ionization energy generally increases across a period in the periodic table. This is because the nuclear charge increases, pulling the electrons closer to the nucleus and making it harder to remove an electron.

(1e)
(1) H⁻, H, H⁺: H⁻ > H > H⁺ (H⁻ has the largest radius due to extra electrons, while H⁺ has the smallest due to loss of an electron).
(2) Si, Cl, P: Cl < P < Si (Atomic radius decreases across a period, so Si has the largest radius).

(1f)
(1) 2-fluoro-3-methylpent-2-ene:
F
|
CH₃-C=C-CH₂-CH₃
|
CH₃

(2) 2,2-dimethylbutane:
CH₃
|
CH₃-C-CH₂-CH₃
|
CH₃

(1g)
1. Melting Point: A pure substance has a sharp and constant melting point.
2. Boiling Point: A pure substance has a sharp and constant boiling point.

(1h)
1. Concentration of Reactants: Higher concentration increases the rate of reaction.
2. Temperature: Increasing temperature increases the rate of reaction.

(1i)
Faraday’s second law states that the mass of a substance deposited or liberated during electrolysis is directly proportional to its chemical equivalent weight (molar mass divided by the number of electrons involved in the reaction).

(1f)
(i)

F
|
CH₃-C=C-CH₂-CH₃
|
CH₃

(ii)

CH₃
|
CH₃-C-CH₂-CH₃
|
CH₃

(2ai)
-The volume of gas molecules is negligible compared to the volume of the container.

-Collisions between gas molecules are perfectly elastic (no energy loss).

(2aii)
Mass of gas = 0.8 g
Volume = 560 cm³ = 0.560 dm³
Temperature (T) = 0 °C = 273 K
Pressure (P) = 1 atm = 101325 N/m²
Gas constant (R) = 8.31 J K⁻¹ mol⁻¹

Using the ideal gas equation:
PV = nRT
n = PV / RT
n = (101325 N/m² × 0.560 × 10⁻³ m³) / (8.31 J K⁻¹ mol⁻¹ × 273 K)
n = 56.742 / 2268.63 = 0.025 mol

Molar mass = Mass / Moles = 0.8 g / 0.025 mol = 32 g/mol

(2b)
(i) Ionization energy increases across a period.
(ii) Oxygen has a lower ionization energy than nitrogen because oxygen has four electrons in the 2p orbital, while nitrogen has three. The extra electron in oxygen causes repulsion, making it easier to remove. Nitrogen has a half-filled 2p orbital, which is more stable and requires more energy to remove an electron.

(2c)
(i) HOCl is acidic: It can donate a proton (H⁺) in solution, forming OCl⁻. The presence of the electronegative chlorine atom makes the O-H bond more polar, facilitating proton donation.
(ii) NaOH is basic: It dissociates in water to form Na⁺ and OH⁻ ions. The OH⁻ ions make the solution basic by accepting protons (H⁺)

*WAEC GCE CHEMISTRY THEORY*

(4a)
(i) Diamond, Graphite.

(ii) In diamond, each carbon atom is bonded to four others in a tetrahedral structure. All electrons are tightly bound, so there are no free electrons to conduct electricity.

(iii)
• In solid NaCl, the ions (Na⁺ and Cl⁻) are held in a fixed lattice structure and cannot move, so there is no flow of charge.
• When NaCl dissolves in water, the ions (Na⁺ and Cl⁻) are free to move, allowing the solution to conduct electricity.

(4b)
(i) Carbon (IV) oxide (CO₂) is a greenhouse gas: It traps heat in the Earth’s atmosphere by absorbing and re-emitting infrared radiation, contributing to global warming.

(ii)
• CaCO₃ —-> CaO + CO₂
• Calcium oxide, Carbon dioxide

(iii)
• Used as a building material and in the production of cement.
• Used to neutralize acidic soils.

(4c)
(i) A mixture of two or more elements, where at least one is a metal, to enhance properties like strength, hardness, or resistance to corrosion.

(ii)
• Brass: Copper (Cu) and Zinc (Zn)
• Duralumin: Aluminum (Al), Copper (Cu), Magnesium (Mg), and Manganese (Mn)
• Bronze: Copper (Cu) and Tin (Sn)

(4d)
(i) It is widely used as a disinfectant for water purification, swimming pools, and household cleaning. It is also used as a bleach for whitening clothes and removing stains

(ii) Used as table salt for seasoning and preserving food.

Used in the production of chemicals like chlorine and sodium hydroxide