ESAT Challenge Chemistry Esat-chem-challenge-2

10 questions10 marks20Updated August 2026

The ESAT Challenge Chemistry Esat-chem-challenge-2 paper in full: all 10 questions, each with its answer. ESAT is the Engineering and Science Admissions Test. Sit it cold under exam timing, mark it, then work back through anything you missed using the solutions below.

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Question 1

1 mark

A scrap dealer assays a batch of copper and zinc alloy. A

5.00\,\text{g}

turning is dropped into an excess of dilute hydrochloric acid; only the zinc reacts, and

1.20\,\text{dm}^3

of hydrogen is collected at room conditions. What percentage of the alloy, by mass, is copper? (

A_r

: Zn

=65

)

A. $35.0\%$
B. $26.0\%$
C. $40.0\%$
D. $55.0\%$
E. $65.0\%$

Answer: A

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Question 2

1 mark

Complete combustion of

0.150\,\text{g}

of a compound of carbon, hydrogen and oxygen only gives

0.220\,\text{g}

of carbon dioxide and

0.090\,\text{g}

of water. The relative molecular mass of the compound is

60

. What is its molecular formula? (

A_r

: C

=12

, H

=1

, O

=16

)

A. $\text{CH}_2\text{O}$
B. $\text{C}_3\text{H}_8\text{O}$
C. $\text{C}_2\text{H}_4\text{O}_2$
D. $\text{C}_2\text{H}_4\text{O}$
E. $\text{C}_3\text{H}_4\text{O}_2$

Answer: C

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Question 3

1 mark

An iron supplement tablet is dissolved in excess dilute sulfuric acid and the solution made up to

250\,\text{cm}^3

. A

25.0\,\text{cm}^3

portion is titrated against

0.0100\,\text{mol dm}^{-3}

potassium manganate(VII), of which

20.0\,\text{cm}^3

is required. All the iron is present as

\text{Fe}^{2+}

, and

\text{MnO}_4^-

is reduced to

\text{Mn}^{2+}

. What mass of iron does one tablet contain? (

A_r

: Fe

=56

)

A. $56\,\text{mg}$
B. $112\,\text{mg}$
C. $280\,\text{mg}$
D. $560\,\text{mg}$
E. $5.60\,\text{g}$

Answer: D

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Question 4

1 mark

1.00\,\text{mol}

of hydrogen and

1.00\,\text{mol}

of iodine vapour are sealed in a

1.00\,\text{dm}^3

vessel and left to reach equilibrium, at which point

1.60\,\text{mol}

of hydrogen iodide is present:

\text{H}_2(\text{g}) + \text{I}_2(\text{g}) \rightleftharpoons 2\text{HI}(\text{g})

. Calculate

K_c

A. $4$
B. $64$
C. $16$
D. $32$
E. $128$

Answer: B

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Question 5

1 mark

A rocket engine burns hydrazine with dinitrogen tetroxide:

2\text{N}_2\text{H}_4(\text{l}) + \text{N}_2\text{O}_4(\text{l}) \to 3\text{N}_2(\text{g}) + 4\text{H}_2\text{O}(\text{g})

. Standard enthalpies of formation, in

\text{kJ mol}^{-1}

, are

\text{N}_2\text{H}_4(\text{l})

+50.6

\text{N}_2\text{O}_4(\text{l})

-19.5

\text{H}_2\text{O}(\text{g})

-241.8

. Find

\Delta H

for the reaction as written.

A. $-885.5$
B. $-967.2$
C. $-1008.9$
D. $-1048.9$
E. $-1130.6$

Answer: D

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Question 6

1 mark

20\,\text{cm}^3

of a gaseous hydrocarbon is mixed with

150\,\text{cm}^3

of oxygen, an excess, and the mixture is sparked. After cooling to the original temperature and pressure the volume is

110\,\text{cm}^3

; after passing the residue through concentrated potassium hydroxide solution,

30\,\text{cm}^3

remains. All volumes are measured at the same temperature and pressure. What is the hydrocarbon?

A. $\text{C}_4\text{H}_6$
B. $\text{C}_4\text{H}_{10}$
C. $\text{C}_5\text{H}_{10}$
D. $\text{C}_3\text{H}_8$
E. $\text{C}_4\text{H}_8$

Answer: E

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Question 7

1 mark

25.0\,\text{cm}^3

0.100\,\text{mol dm}^{-3}

ethanoic acid (

K_a = 1.8\times10^{-5}\,\text{mol dm}^{-3}

) is titrated with

0.100\,\text{mol dm}^{-3}

sodium hydroxide. What is the pH after

12.5\,\text{cm}^3

of the alkali has been added? (Take

\log_{10} 1.8 \approx 0.26

A. $2.87$
B. $7.00$
C. $8.72$
D. $4.74$
E. $9.26$

Answer: D

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Question 8

1 mark

A bench-scale cell electrolyses molten aluminium oxide. A current of

0.500\,\text{A}

is passed for

32

minutes and

10

seconds. What mass of aluminium is deposited at the cathode? (

A_r

: Al

=27

)

A. $0.030\,\text{g}$
B. $0.270\,\text{g}$
C. $0.090\,\text{g}$
D. $0.900\,\text{g}$
E. $2.70\,\text{g}$

Answer: C

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Question 9

1 mark

2-methylbutane is treated with chlorine in ultraviolet light. How many different monochlorinated products are possible, ignoring stereoisomerism?

A. $3$
B. $5$
C. $6$
D. $4$
E. $8$

Answer: D

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Question 10

1 mark

10.0\,\text{g}

mixture of calcium carbonate and calcium oxide is heated strongly until there is no further change in mass, leaving

7.80\,\text{g}

of solid. What percentage of the original mixture, by mass, was calcium carbonate? (

A_r

: Ca

=40

, C

=12

, O

=16

)

A. $22.0\%$
B. $44.0\%$
C. $50.0\%$
D. $56.0\%$
E. $78.0\%$

Answer: C

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