JAMB Chemistry Past Questions 2025

10 questions from the JAMB 2025 Chemistry paper, with answers, and explanations for 9 of them. Tap "Show answer" under each one when you are ready.

JAMB 2025Question 1 · Chemistry of Non-metals and Gases

The expression

\frac{P _{1} V _{1}}{T _{1}} = \frac{P _{2} V _{2}}{T _{2}}

represents

A.Avogadro's law
B.Boyle's law
C.General gas law
D.Charles' law

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Answer: C. General gas law

This expression combines Boyle's law and Charles' law into the general (combined) gas law, relating pressure, volume and temperature of a fixed mass of gas.

JAMB 2025Question 2 · Electrochemistry and Redox Reactions

The time required to deposit

4.5 g

of copper from

C u S O_{4}

solution by passing a current of 2.5 Amperes is (Cu =

64 g

; 1F =

96500 C mo l^{- 1}

)

A.2714 sec
B.2527 sec
C.5428 sec
D.6785 sec

Show answer

Answer: C. 5428 sec

$Q = I t$ ; mass $4.5 g \times \frac{2 \times 96500}{64} = 13570.3 C$ ; $t = \frac{13570.3}{2.5} \approx 5428$ sec.

JAMB 2025Question 3 · Electrochemistry and Redox Reactions

In the electrolysis of molten sodium chloride, sodium ions are discharged at the cathode (

N a^{+} + e^{-} \to N a

) while chlorine gas is liberated at the anode. This industrial method of producing sodium metal is known as the

A.Bessemer process
B.Chlor-alkali process
C.Downs process
D.Bosch process

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Answer: C. Downs process

The Downs process is the industrial electrolysis of molten sodium chloride used to extract sodium metal and chlorine gas.

JAMB 2025Question 4 · Organic Chemistry

Consider the reaction:

C H_{4} + C l_{2} UV light C H_{3} C l + H C l

. This reaction is best classified as

A.neutralization
B.substitution
C.polymerization
D.oxidation

Show answer

Answer: B. substitution

A hydrogen atom in methane is replaced (substituted) by a chlorine atom, so this is a substitution reaction, typical of alkanes reacting with halogens under UV light.

JAMB 2025Question 5 · Organic Chemistry

What is the IUPAC name of the ester with structural formula

C H_{3} C H_{2} C O O C_{2} H_{5}

A.propyl ethanoate
B.ethyl ethanoate
C.ethyl propanoate
D.propyl methanoate

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Answer: C. ethyl propanoate

The acid part ( $C H_{3} C H_{2} C O O -$ ) comes from propanoic acid, giving 'propanoate', and the alcohol part ( $- C_{2} H_{5}$ ) comes from ethanol, giving 'ethyl' — hence ethyl propanoate.

JAMB 2025Question 6 · Organic Chemistry

The compound with structural formula

C H_{3} - C O - N H_{2}

belongs to which class of organic compounds?

A.alkylamine
B.alkanone
C.alkanamide
D.amino acid

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Answer: C. alkanamide

$C H_{3} C O N H_{2}$ (ethanamide) contains the $- C O N H_{2}$ functional group, characteristic of an alkanamide (amide).

JAMB 2025Question 7 · Physical Chemistry

For the reversible reaction

X_{2} + 3 Y_{2} ⇌ 2 X Y_{3}

, the expression for the equilibrium constant,

K_{c}

, is

A. $\frac{[ 2 X Y _{3} ]}{[ X _{2} ] [ 3 Y _{2} ]}$
B. $\frac{[ X _{2} ] [ 3 Y _{2} ]}{[ 2 X Y _{3} ]}$
C. $\frac{[ X Y _{3} ] ^{2}}{[ X _{2} ] [ Y _{2} ]}$
D. $\frac{[ X Y _{3} ] ^{2}}{[ X _{2} ] [ Y _{2} ] ^{3}}$

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Answer: D. $\frac{[ X Y _{3} ] ^{2}}{[ X _{2} ] [ Y _{2} ] ^{3}}$

$K_{c}$ is written as the concentration of products over reactants, each raised to the power of its stoichiometric coefficient: $K_{c} = \frac{[ X Y _{3} ] ^{2}}{[ X _{2} ] [ Y _{2} ] ^{3}}$ .

JAMB 2025Question 8 · Quantitative Chemistry

What is the molecular mass of an alkanoic acid, if 0.5 mole of the acid weighs

44 g

A.72
B.88
C.60
D.46

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Answer: B. 88

Molar mass $= \frac{44 g}{0.5 m o l} = 88 g / m o l$ .

JAMB 2025Question 9 · Quantitative Chemistry

On heating

12.5 g

of saturated solution to dryness at

6 0^{\circ} C

2 g

of anhydrous salt was recovered, calculate its solubility in grams per

100 g

of water.

A.16.0
B.4.0
C.2.0
D.20.0

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Answer: D. 20.0

Solvent $= 12.5 g - 2 g = 10.5 g$ ; solubility $= \frac{2}{10.5} \times 100 \approx 19.05$ , rounded to nearest option, $20.0 g$ per $100 g$ water.

JAMB 2025Question 10 · Acids, Bases, and Salts

Calculate the pH of 0.001M

K O H

solution.

A.11
B.14
C.12
D.3

Show answer

Answer: A. 11

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