JAMB Chemistry Past Questions 2019

10 questions from the JAMB 2019 Chemistry paper, with answers and explanations. Tap "Show answer" under each one when you are ready.

JAMB 2019Question 1 · Acids, Bases, and Salts

_{2}

_{3}

+ 2HCl

\to

2NaCl + H

_{2}

O + CO

_{2}

The indicator most suitable for this reaction should have a pH equal to

Show answer

Answer: C. 3

Since excess $C O_{2}$ makes the solution slightly acidic near the endpoint of this carbonate-acid titration, an indicator changing colour around pH 3 (such as methyl orange) is most suitable.

JAMB 2019Question 2 · Atomic Structure and Chemical Bonding

Which of the following pairs cannot be represented with a chemical formula?

A.air and bronze
B.bronze and sodium chloride
C.copper and sodium chloride
D.caustic soda and washing soda

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Answer: A. air and bronze

Air (a gas mixture) and bronze (a metal alloy/mixture) are both mixtures of variable composition and cannot be represented by a single fixed chemical formula.

JAMB 2019Question 3 · Atomic Structure and Chemical Bonding

An element Z contains 80% of

_{8}^{16}

Z and 20% of

_{8}^{18}

Z. Its relative atomic mass is

A.16.2
B.17.6
C.16.0
D.16.4

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Answer: D. 16.4

Relative atomic mass = (0.80x16)+(0.20x18) = 12.8+3.6 = 16.4.

JAMB 2019Question 4 · Chemistry of Non-metals and Gases

Which two gases can be used for the demonstration of the fountain experiment?

A.SO $_{4}$ and NH $_{3}$
B.SO $_{3}$ and NH $_{3}$
C.HCl and NH $_{3}$
D.SO $_{2}$ and CO

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Answer: C. HCl and NH $_{3}$

HCl and $N H_{3}$ are both extremely soluble gases, making them classic choices for demonstrating the fountain experiment.

JAMB 2019Question 5 · Electrochemistry and Redox Reactions

What mass of magnesium would be obtained by passing a current of 2 amperes for 2 hours

30 min s

, through molten magnesium chloride? [1 faraday =

96500 C

, Mg = 24]

A. $1.12 g$
B. $4.48 g$
C. $1.80 g$
D. $2.24 g$

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Answer: D. $2.24 g$

Q = It = 2 x $9000 s$ = $18000 C$ . Moles electrons = $\frac{18000}{96500}$ = $0.1865 mol$ . $M g^{2 +}$ +2e- → Mg, so moles Mg = $0.0933 mol$ ; mass = 0.0933x24 = $2.24 g$ .

JAMB 2019Question 6 · Environmental and Industrial Chemistry

A radioactive nucleus has a half-life of 20 years, starting with 100,000 particles, how many particles will be left exactly at the end of 40 years

A.75,000 particles
B.35,000 particles
C.25,000 particles
D.50,000 particles

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Answer: C. 25,000 particles

After two half-lives (40 years / 20 years each), the amount remaining = 100,000 x $(1/2)^{2}$ = 25,000 particles.

JAMB 2019Question 7 · Organic Chemistry

2-methylprop-1-ene is an isomer of?

A.3-methyl but-1-ene
B.2-methyl but-1-ene
C.but-2-ene
D.pent-2-ene

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Answer: C. but-2-ene

2-methylprop-1-ene has formula $C_{4} H_{8}$ ; among the options, only but-2-ene shares this molecular formula (the others are $C_{5} H_{10}$ ).

JAMB 2019Question 8 · Organic Chemistry

X is a substance which liberates CO

_{2}

on treatment with concentrated H

_{2}

_{4}

. A warm solution of X can decolorize acidified KMnO

_{4}

. X is

A.HCOOH
B.NaHCO $_{3}$
C.FeCO $_{3}$
D.H $_{2}$ C $_{2}$ O $_{4}$

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Answer: D. H $_{2}$ C $_{2}$ O $_{4}$

Ethanedioic (oxalic) acid, $H_{2} C_{2} O_{4}$ , releases $C O_{2}$ (with CO) on treatment with concentrated $H_{2} S O_{4}$ , and its warm solution decolorizes acidified $KMn O_{4}$ by reducing it.

JAMB 2019Question 9 · Physical Chemistry

Which of the following statements about catalyst is false?

A.biological catalysts are called enzymes
B.catalyst do not appear in the balanced equation
C.catalyst reduce the activation energy for a reaction
D.catalysts do not alter the mechanism of the reaction and never appear in the rate low

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Answer: D. catalysts do not alter the mechanism of the reaction and never appear in the rate low

Catalysts actually do alter the reaction mechanism (providing an alternative lower-energy pathway) and can appear in the rate law of a catalyzed reaction, making this statement false.

JAMB 2019Question 10 · Quantitative Chemistry

A certain hydrocarbon on complete combustion at s.t.p produced

89.6 d m^{3}

of CO

_{2}

and

54 g

of water. The hydrocarbon should be?

A.C $_{6}$ H $_{6}$
B.C $_{4}$ H $_{10}$
C.C $_{5}$ H $_{10}$
D.C $_{4}$ H $_{6}$

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Answer: D. C $_{4}$ H $_{6}$

Moles $C O_{2}$ = $\frac{89.6}{22.4}$ = $4 mol$ (4 carbons). Moles $H_{2} O$ = $\frac{54}{18}$ = $3 mol$ , giving 6 hydrogens. Hydrocarbon formula: $C_{4} H_{6}$ .

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JAMB Chemistry Past Questions 2019

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