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ESAT Mock Chemistry ESAT-CHEM-MOCK-1

27 questions27 marks40Updated July 2026

The ESAT Mock Chemistry ESAT-CHEM-MOCK-1 paper in full: all 27 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

Consider a neutral atom of

^{24}\text{Mg}

and the magnesium ion

^{24}\text{Mg}^{2+}

. The atomic number of magnesium is 12.

Which of the following quantities is/are the same for both the neutral atom and the ion?

1. The number of protons in the nucleus
2. The number of neutrons in the nucleus
3. The number of electrons orbiting the nucleus

2.1, 2 and 3
A.1 only
B.2 only
C.1 and 2 only
D.1 and 3 only

Answer: C

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Question 2

1 mark

Phosphorus has an atomic number of 15. Which of the following correctly describes the composition of a neutral atom of the isotope

^{31}\text{P}

?

A.15 protons, 16 neutrons, and an electron configuration of 2, 8, 5
B.15 protons, 31 neutrons, and an electron configuration of 2, 8, 5
C.16 protons, 15 neutrons, and an electron configuration of 2, 8, 6
D.15 protons, 16 neutrons, and an electron configuration of 2, 13
E.31 protons, 15 neutrons, and an electron configuration of 2, 8, 5

Answer: A

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Question 3

1 mark

An ion of a specific isotope is denoted as

Q^{2+}

. The ion has a nucleon number of 40 and contains 22 neutrons. What is the ratio of the total number of subatomic particles located in the nucleus to the total number of electrons in this ion?

A.2.00
B.2.22
C.2.50
D.1.82
E.2.11

Answer: C

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Question 4

1 mark

In a simplified model of an atom, the radius of the atom is approximately

10^5

times larger than the radius of its nucleus. Assuming the nucleus contains nearly all the mass of the atom, what is the approximate ratio of the average density of the nucleus to the average density of the whole atom?

A.10^{5}
B.10^{10}
C.10^{15}
D.10^{-15}
E.1

Answer: C

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Question 5

1 mark

An ion of element

X

is represented by the symbol

^{A}_{Z}X^{n+}

. The relationship between the atomic number, mass number, and number of electrons (

e

) for this ion is given by the equations below:

A = 2Z + 3

e = Z - 3

Which of the following statements about this ion is/are correct?

1. The value of the charge

n

is equal to 3.
2. The number of neutrons in the ion is

Z + 3

.
3. The total number of subatomic particles (protons, neutrons, and electrons) in the ion is equal to

3Z

.

A.1 only
B.2 only
C.1 and 2 only
D.2 and 3 only
E.1, 2 and 3

Answer: E

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Question 6

1 mark

An atom has the atomic number 19. Which of the following options correctly identifies the electron configuration, the Period, and the Group of this element in the Periodic Table?

0.Configuration: 2,8,7,2; Period: 4; Group: 2
A.Configuration: 2,8,9; Period: 3; Group: 9
B.Configuration: 2,8,8,1; Period: 3; Group: 1
C.Configuration: 2,8,8,1; Period: 4; Group: 1
D.Configuration: 2,8,8,1; Period: 4; Group: 19
E.Configuration: 2,8,7,2; Period: 4; Group: 2

Answer: C

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Question 7

1 mark

The relative formula mass of an anhydrous metal carbonate

M_2\text{CO}_3

is

138.2

. The metal ion

M^{+}

present in this compound is isoelectronic with a neutral atom of the noble gas Argon (

Z = 18

). Element

M

consists of two naturally occurring isotopes with mass numbers

39

and

41

. Given that the relative formula mass of the carbonate ion

\text{CO}_3^{2-}

is

60.0

, what is the percentage abundance of the heavier isotope of

M

in this sample?

A.5.0%
B.10.0%
C.50.0%
D.90.0%
E.95.0%

Answer: A

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Question 8

1 mark

A metal

X

has only one stable isotope,

^{121}X

. A halogen

Y

has two naturally occurring isotopes:

^{35}Y

(with an abundance of 75%) and

^{37}Y

(with an abundance of 25%). A sample of the compound

XY_2

is analyzed in a mass spectrometer. Focusing only on the molecular ion

XY_2^{+}

, how many peaks are observed in this region of the spectrum, and what is the ratio of the abundance of the peak with the lowest

m/z

value to the peak with the highest

m/z

value?

A.2 peaks; ratio 3:1
B.3 peaks; ratio 1:1
C.3 peaks; ratio 3:1
D.3 peaks; ratio 9:1
E.4 peaks; ratio 9:1

Answer: D

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Question 9

1 mark

Element

\text{X}

is located in Period 3 and Group 16 of the Periodic Table.

A specific sample of element

\text{X}

contains only two isotopes:

^{32}\text{X}

and

^{34}\text{X}

. In this sample, the ratio of the abundance of atoms of

^{32}\text{X}

to atoms of

^{34}\text{X}

is

9:1

.

What is the relative atomic mass (

A_r

) of

\text{X}

in this sample, and how many neutrons are present in the nucleus of the heavier isotope?

A. $A_r = 32.2$ ; neutrons = 18
B. $A_r = 32.2$ ; neutrons = 16
C. $A_r = 33.0$ ; neutrons = 18
D. $A_r = 33.8$ ; neutrons = 18
E. $A_r = 33.8$ ; neutrons = 16

Answer: A

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Question 10

1 mark

The element

M

is located in Period 3, Group 2 of the Periodic Table. The element

X

is located in Period 3, Group 17. Which of the following is correct regarding these elements and the compound they form?

A.Element $M$ is a non-metal and element $X$ is a metal.
B.They react to form an ionic compound with the formula $MX_2$ .
C.They react to form a covalent compound with the formula $MX_2$ .
D.Element $X$ has a larger atomic radius than element $M$ .
E.Element $M$ has a higher first ionisation energy than element $X$ .

Answer: B

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Question 11

1 mark

Consider the layout of the Periodic Table according to IUPAC conventions. What is the atomic number (

Z

) of the element located in Period 4 and Group 15?

A.15
B.31
C.33
D.35
E.51

Answer: C

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Question 12

1 mark

Elements

P, Q, R,

and

S

have consecutive atomic numbers

n, n+1, n+2,

and

n+3

respectively. Element

R

is a noble gas in Period 3. Which of the following statements about these elements is correct?

A.Element $P$ is a metal in Group 16.
B.Element $Q$ forms a stable ion with a $1+$ charge.
C.Element $S$ is an alkali metal in Group 1.
D.Element $P$ is in Period 2.
E.The oxide of element $S$ has an acidic character.

Answer: C

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Question 13

1 mark

The elements in the Periodic Table are arranged by increasing atomic number. Element

T

is located in Group 14 and Period 3. Which of the following statements is correct?

A.The element with atomic number $Z-1$ (where $Z$ is the atomic number of $T$ ) is a non-metal.
B.The element with atomic number $Z+1$ is in Group 15.
C.Element $T$ forms a stable ion with a $4+$ charge in aqueous solution.
D.The element directly above $T$ in the Periodic Table has an atomic number of 7.
E.Element $T$ is a gas at room temperature and pressure.

Answer: B

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Question 14

1 mark

The first five successive ionisation energies of an element

Y

are

738

,

1451

,

7733

,

10543

, and

13630\,\text{kJ}\,\text{mol}^{-1}

.

Y

is in Period 3 of the Periodic Table.

Which of the following statements about

Y

is/are correct?

1. It is an alkaline earth metal.
2. It reacts with oxygen to form a compound with the formula

Y_2O

.
3. It has a smaller atomic radius than the element in Period 3, Group 17.

A.1 only
B.2 only
C.3 only
D.1 and 2 only
E.1 and 3 only

Answer: A

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Question 15

1 mark

Three elements are identified by their positions in the Periodic Table:

- Element X: Period 4, Group 2
- Element Y: Period 3, Group 16
- Element Z: Period 2, Group 17

Which of the following lists these elements in order of increasing first ionisation energy?

A. $X < Y < Z$
B. $Y < X < Z$
C. $Z < Y < X$
D. $X < Z < Y$
E. $Y < Z < X$

Answer: A

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Question 16

1 mark

A student investigates the reactivity of three Group 1 metals by adding small, equal-sized pieces of lithium, sodium, and potassium to separate troughs of water. The following observations are recorded:
- Metal

M_1

: Fizzes steadily and moves slowly across the surface until it disappears.
- Metal

M_2

: Fizzes rapidly, melts into a shiny ball, and skims quickly across the surface.
- Metal

M_3

: Reacts violently, producing a lilac flame and a small explosion.
Which of the following correctly identifies the metals and provides the correct explanation for the trend in reactivity observed?

0. $M_1 = \text{Na}, M_2 = \text{Li}, M_3 = \text{K}$ ; reactivity increases down the group because atomic mass increases.
A. $M_1 = \text{Li}, M_2 = \text{Na}, M_3 = \text{K}$ ; reactivity increases down the group as the outermost electron is further from the nucleus.
B. $M_1 = \text{K}, M_2 = \text{Na}, M_3 = \text{Li}$ ; reactivity increases down the group as the outermost electron is further from the nucleus.
C. $M_1 = \text{Li}, M_2 = \text{Na}, M_3 = \text{K}$ ; reactivity decreases down the group as the nuclear charge increases.
E. $M_1 = \text{Li}, M_2 = \text{Na}, M_3 = \text{K}$ ; reactivity increases down the group because the first ionisation energy increases.

Answer: A

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Question 17

1 mark

The reactivity of Group 17 elements (the halogens) can be compared using displacement reactions. A student mixes aqueous solutions of halogens with aqueous solutions of sodium halides. In which of the following mixtures will a displacement reaction occur?
1.

\text{Cl}_2(aq) + 2\text{NaI}(aq)

2.

\text{I}_2(aq) + 2\text{NaBr}(aq)

3.

\text{Br}_2(aq) + 2\text{NaCl}(aq)

4.

\text{Br}_2(aq) + 2\text{NaI}(aq)

A.1 and 2 only
B.1 and 4 only
C.2 and 3 only
D.3 and 4 only
E.1, 3, and 4 only

Answer: B

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Question 18

1 mark

A sample of

1.30\,\text{g}

of pure

^{13}\text{C}

is completely burned in an excess of

^{16}\text{O}_2

to form

^{13}\text{C}^{16}\text{O}_2

. Given that the Avogadro constant

N_A = 6.0 \times 10^{23}\,\text{mol}^{-1}

and the atomic numbers (

Z

) of carbon and oxygen are

6

and

8

respectively, what is the total number of neutrons in the nuclei of the product molecules?

A. $4.2 \times 10^{23}$
B. $1.32 \times 10^{24}$
C. $1.38 \times 10^{24}$
D. $1.50 \times 10^{24}$
E. $2.70 \times 10^{24}$

Answer: C

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Question 19

1 mark

In the formation of the ionic compound magnesium fluoride from its elements (

2\text{Mg} + \text{F}_2 \rightarrow 2\text{MgF}_2

is incorrect, the stoichiometry is

\text{Mg} + \text{F}_2 \rightarrow \text{MgF}_2

), which of the following statements correctly describes the fundamental rearrangement of subatomic particles according to the principles of chemical reactions?

A.Each magnesium nucleus loses two valence electrons, which are then captured by the nuclei of two fluorine atoms.
B.The total number of protons and neutrons in the system remains constant, while the valence electrons of each magnesium atom are transferred to fluorine atoms.
C.The fluorine atoms undergo nuclear transmutation to achieve a stable noble-gas electron configuration.
D.The mass of the products is exactly equal to the mass of the reactants because the total number of atoms, electrons, and photons is conserved.
E.Electrons are transferred from the fluorine atoms to the magnesium atoms to establish a stable crystal lattice.

Answer: B

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Question 20

1 mark

Which one of the following rows correctly identifies the chemical formulae for the covalent molecules methane, ammonia, and sulfur dioxide?

A.methane: $CH_4$ ; ammonia: $NH_4$ ; sulfur dioxide: $SO_2$
B.methane: $CH_3$ ; ammonia: $NH_3$ ; sulfur dioxide: $SO_2$
C.methane: $CH_4$ ; ammonia: $NH_3$ ; sulfur dioxide: $SO_2$
D.methane: $CH_4$ ; ammonia: $NH_3$ ; sulfur dioxide: $SO_3$
E.methane: $C_2H_4$ ; ammonia: $NH_3$ ; sulfur dioxide: $SO_2$

Answer: C

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Question 21

1 mark

A student needs to calculate the relative formula mass (

M_r

) of sodium carbonate for a titration experiment.

Using the relative atomic masses:

Ar(Na) = 23.0

,

Ar(C) = 12.0

,

Ar(O) = 16.0

, what is the relative formula mass of sodium carbonate?

A.83.0
B.90.0
C.106.0
D.74.0
E.143.0

Answer: C

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Question 22

1 mark

Which one of the following chemical formulae is correctly matched to its compound name?

A.ammonium nitrate, $NH_4(NO_3)_2$
B.copper(II) chloride, $Cu_2Cl$
C.iron(III) hydroxide, $Fe(OH)_3$
D.potassium sulfate, $KSO_4$
E.silver chloride, $AgCl_2$

Answer: C

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Question 23

1 mark

An aqueous solution of barium hydroxide is reacted with an aqueous solution of sulfuric acid. This reaction produces a white precipitate of barium sulfate and liquid water. Which of the following is the correctly balanced chemical equation for this reaction, including all state symbols?

0. $\text{Ba(OH)}_2(\text{s}) + \text{H}_2\text{SO}_4(\text{aq}) \rightarrow \text{BaSO}_4(\text{s}) + 2\text{H}_2\text{O}(\text{l})$
A. $\text{Ba(OH)}_2(\text{aq}) + \text{H}_2\text{SO}_4(\text{aq}) \rightarrow \text{BaSO}_4(\text{aq}) + 2\text{H}_2\text{O}(\text{l})$
B. $\text{Ba(OH)}_2(\text{aq}) + \text{H}_2\text{SO}_4(\text{aq}) \rightarrow \text{BaSO}_4(\text{s}) + 2\text{H}_2\text{O}(\text{aq})$
C. $\text{Ba(OH)}_2(\text{aq}) + \text{H}_2\text{SO}_4(\text{aq}) \rightarrow \text{BaSO}_4(\text{s}) + 2\text{H}_2\text{O}(\text{l})$
E. $\text{BaOH}(\text{aq}) + \text{H}_2\text{SO}_4(\text{aq}) \rightarrow \text{BaSO}_4(\text{s}) + \text{H}_2\text{O}(\text{l})$

Answer: C

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Question 24

1 mark

Octane (

\text{C}_8\text{H}_{18}

) is a liquid fuel. Which of the following equations correctly represents the complete combustion of octane in excess oxygen at

25^\circ\text{C}

and

100\,\text{kPa}

including state symbols?

A. $2\text{C}_8\text{H}_{18}(\text{l}) + 25\text{O}_2(\text{g}) \rightarrow 16\text{CO}_2(\text{g}) + 18\text{H}_2\text{O}(\text{l})$
B. $2\text{C}_8\text{H}_{18}(\text{g}) + 25\text{O}_2(\text{g}) \rightarrow 16\text{CO}_2(\text{g}) + 18\text{H}_2\text{O}(\text{g})$
C. $2\text{C}_8\text{H}_{18}(\text{l}) + 25\text{O}_2(\text{g}) \rightarrow 16\text{CO}_2(\text{g}) + 18\text{H}_2\text{O}(\text{g})$
D. $\text{C}_8\text{H}_{18}(\text{l}) + 12\text{O}_2(\text{g}) \rightarrow 8\text{CO}_2(\text{g}) + 9\text{H}_2\text{O}(\text{l})$
E. $2\text{C}_8\text{H}_{18}(\text{l}) + 17\text{O}_2(\text{g}) \rightarrow 16\text{CO}(\text{g}) + 18\text{H}_2\text{O}(\text{l})$

Answer: A

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Question 25

1 mark

A piece of magnesium ribbon is placed into a beaker containing an aqueous solution of silver nitrate. A displacement reaction occurs, producing solid silver and aqueous magnesium nitrate. Which of the following represents the balanced net ionic equation for this reaction including state symbols?

A. $\text{Mg}(\text{s}) + 2\text{Ag}^+(\text{aq}) \rightarrow \text{Mg}^{2+}(\text{aq}) + 2\text{Ag}(\text{s})$
B. $\text{Mg}(\text{s}) + \text{Ag}^+(\text{aq}) \rightarrow \text{Mg}^{2+}(\text{aq}) + \text{Ag}(\text{s})$
C. $\text{Mg}(\text{s}) + 2\text{AgNO}_3(\text{aq}) \rightarrow \text{Mg(NO}_3)_2(\text{aq}) + 2\text{Ag}(\text{s})$
D. $\text{Mg}^{2+}(\text{aq}) + 2\text{Ag}(\text{s}) \rightarrow \text{Mg}(\text{s}) + 2\text{Ag}^+(\text{aq})$
E. $\text{Mg}(\text{aq}) + 2\text{Ag}^+(\text{s}) \rightarrow \text{Mg}^{2+}(\text{s}) + 2\text{Ag}(\text{aq})$

Answer: A

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Question 26

1 mark

The dichromate(VI) ion,

\text{Cr}_2\text{O}_7^{2-}

, reacts with iodide ions,

\text{I}^-

, in an acidic solution to produce chromium(III) ions,

\text{Cr}^{3+}

, iodine,

\text{I}_2

, and water.

A partially balanced equation for this reaction is:

\text{Cr}_2\text{O}_7^{2-} + a\text{I}^- + b\text{H}^+ \rightarrow 2\text{Cr}^{3+} + d\text{I}_2 + 7\text{H}_2\text{O}

What is the value of the sum

a + b + d

in the simplest balanced equation?

A.16
B.19
C.23
D.26
E.33

Answer: C

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Question 27

1 mark

Consider the following reversible gas-phase reaction at equilibrium in a closed container:

\text{PCl}_3(\text{g}) + \text{Cl}_2(\text{g}) \rightleftharpoons \text{PCl}_5(\text{g})

The forward reaction is exothermic (

\Delta H = -88\,\text{kJ}\,\text{mol}^{-1}

).

Which of the following changes, when applied independently and assuming all other conditions remain constant, will increase the equilibrium yield of

\text{PCl}_5(\text{g})

?

1. Increasing the temperature
2. Decreasing the volume of the container
3. Adding more

\text{Cl}_2(\text{g})

A.1 only
B.2 only
C.3 only
D.2 and 3 only
E.1, 2 and 3

Answer: D

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