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ESAT Chemistry practice questions

27 questions on moles, bonding, energetics, rates, equilibrium, redox, acids and organic chemistry. Same number of questions and time limit as the real ESAT Chemistry.

All questions are written by Keiko Study in the official format; they are not official ESAT papers.

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Question 1

Atomic structure: ions

How many protons, neutrons and electrons are there in one $_{16}^{34} S^{2 -}$ ion?

16 protons, 18 neutrons, 16 electrons16 protons, 18 neutrons, 18 electrons16 protons, 18 neutrons, 14 electrons18 protons, 16 neutrons, 18 electrons16 protons, 34 neutrons, 18 electrons18 protons, 18 neutrons, 16 electrons

Question 2

Isotopes and relative atomic mass

Element Q has only two naturally occurring isotopes, $^{69} Q$ and $^{71} Q$ . The relative atomic mass of Q is 69.8.

What percentage of the atoms in a natural sample of Q are $^{69} Q$ ?

Question 3

Electron configuration and the Periodic Table

An ion of element Z has the formula $Z^{3 -}$ and the electron configuration 2,8,8.

In which Group and Period of the Periodic Table is element Z?

Question 4

Structure, bonding and properties

The table gives some properties of six substances, P to U.

Which substance is made of simple molecules held together by the strongest intermolecular forces?

Substance	Melting point / °C	Boiling point / °C	Conductivity of solid	Conductivity of liquid
P	−95	69	poor	poor
Q	114	184	poor	poor
R	801	1413	poor	good
S	−7	59	poor	poor
T	1710	2230	poor	poor
U	98	883	good	good

Question 5

Balancing redox equations

Copper reacts with dilute nitric acid to form copper(II) nitrate, nitrogen monoxide and water:

$C u + H N O_{3} \to C u (N O_{3})_{2} + N O + H_{2} O$

When this equation is balanced using the smallest possible whole numbers, what number appears in front of $H N O_{3}$ ?

Question 6

Moles and the Avogadro constant

How many oxygen atoms are there in 4.9 g of sulfuric acid, $H_{2} S O_{4}$ ?

(Relative atomic masses: H = 1, O = 16, S = 32. Avogadro constant = $6.0 \times 10^{23}$ mol⁻¹)

Question 7

Formula of a hydrated salt

A sample of hydrated magnesium sulfate, $M g S O_{4} \cdot x H_{2} O$ , has a mass of 4.92 g. It is heated until all the water of crystallisation has been driven off, leaving 2.40 g of anhydrous magnesium sulfate.

What is the value of $x$ ?

(Relative atomic masses: H = 1, O = 16, Mg = 24, S = 32)

Question 8

Limiting reactant and percentage yield

Aluminium reacts with chlorine:

$2 A l + 3 C l_{2} \to 2 A l C l_{3}$

In an experiment, 8.1 g of aluminium was heated with 21.3 g of chlorine, and 21.36 g of aluminium chloride was collected.

What was the percentage yield, to the nearest whole number?

(Relative atomic masses: Al = 27, Cl = 35.5)

Question 9

Formulae from gas volumes

10 cm³ of a gaseous hydrocarbon was burned completely in excess oxygen. The reaction used 45 cm³ of oxygen and produced 30 cm³ of carbon dioxide. All volumes were measured at the same temperature and pressure.

What is the molecular formula of the hydrocarbon?

Question 10

Titration calculations

25.0 cm³ of sodium hydroxide solution was exactly neutralised by 20.0 cm³ of 0.150 mol dm⁻³ sulfuric acid.

What was the concentration of the sodium hydroxide solution, in g dm⁻³?

(Relative atomic masses: H = 1, O = 16, Na = 23)

Question 11

Oxidation states

In which pair does sulfur have the same oxidation state in both species?

Question 12

Disproportionation

Which of the following reactions is/are disproportionation reactions?

1. $C l_{2} + 2 N a O H \to N a C l + N a C l O + H_{2} O$

2. $N H_{4} N O_{3} \to N_{2} O + 2 H_{2} O$

3. $2 H_{2} O_{2} \to 2 H_{2} O + O_{2}$

Question 13

Group 1 and Group 17 trends

Astatine, At, is the element below iodine in Group 17.

Which of the following statements is/are correct?

1. Chlorine water reacts with aqueous potassium iodide to form iodine.

2. Bromine would be expected to oxidise astatide ions, $A t^{-}$ , to astatine.

3. Lithium reacts more vigorously with water than sodium does.

Question 14

Reactivity series: displacement

Four metals, W, X, Y and Z, were tested with solutions of each other's sulfates. Only the four results in the table were recorded.

Which one of the following conclusions must be correct?

Metal added	Solution	Result
W	sulfate of Z	a coating of Z forms on W
X	sulfate of W	no reaction
Y	sulfate of X	a coating of X forms on Y
Y	sulfate of W	no reaction

W is the most reactive of the four metals.X is the least reactive of the four metals.Y is more reactive than Z.Z would displace X from a solution of the sulfate of X.Y would displace Z from a solution of the sulfate of Z.The order of reactivity, most reactive first, is W, Y, X, Z.

Question 15

Chromatography and Rf values

A food colouring was analysed by paper chromatography. When the paper was removed, the solvent front was 12.0 cm above the baseline. The colouring gave two spots, with centres 3.0 cm and 7.2 cm above the baseline.

The table gives the Rf values of six permitted dyes in the same solvent.

Which two dyes are most likely to be in the colouring?

Dye	Rf value
J	0.20
K	0.25
L	0.30
M	0.60
N	0.72
P	0.84

Question 16

pH and dilution

A solution of hydrochloric acid has a pH of 1.0. A student wants to make a solution with a pH of 3.0 by adding pure water to 10 cm³ of this acid.

What volume of water must be added?

Question 17

Tests for ions

A solution of a salt, S, was tested.

Adding aqueous sodium hydroxide gave a green precipitate.

Adding dilute hydrochloric acid and then aqueous barium chloride gave a white precipitate.

What is S?

Question 18

Rates of reaction

In an experiment, 1.00 g of calcium carbonate lumps was added to 50 cm³ of 1.0 mol dm⁻³ hydrochloric acid at 20 °C. The volume of carbon dioxide was measured until the reaction stopped.

$C a C O_{3} + 2 H C l \to C a C l_{2} + H_{2} O + C O_{2}$

Which of the following changes, each made on its own, would increase the initial rate of reaction without changing the final volume of carbon dioxide?

1. Using 2.00 g of the same calcium carbonate lumps

2. Using 1.00 g of powdered calcium carbonate

3. Using 25 cm³ of 2.0 mol dm⁻³ hydrochloric acid

(Relative formula mass: $C a C O_{3}$ = 100)

Question 19

Activation energy and catalysts

The table describes the energy profile of a reaction with and without a catalyst. All values are enthalpies in kJ mol⁻¹, measured from the same reference level.

What is the activation energy of the reverse reaction when the catalyst is present?

Point on the energy profile	Enthalpy / kJ mol⁻¹
Reactants	+50
Products	−30
Highest point, no catalyst	+120
Highest point, with catalyst	+80

Question 20

Bond enthalpy calculations

Hydrazine, $N_{2} H_{4}$ , burns in oxygen. In a hydrazine molecule the two nitrogen atoms are joined by a single bond, and each nitrogen atom is also bonded to two hydrogen atoms.

$N_{2} H_{4} (g) + O_{2} (g) \to N_{2} (g) + 2 H_{2} O (g)$

Use the mean bond enthalpies in the table to estimate the enthalpy change of this reaction.

Bond	Mean bond enthalpy / kJ mol⁻¹
N–N	158
N–H	391
O=O	498
N≡N	945
O–H	464

Question 21

Calorimetry

40.0 cm³ of 1.00 mol dm⁻³ hydrochloric acid was mixed with 60.0 cm³ of 1.00 mol dm⁻³ sodium hydroxide solution in an insulated cup. The temperature rose by 5.0 °C.

Assume the mixture has a density of 1.00 g cm⁻³ and a specific heat capacity of 4.2 J g⁻¹ °C⁻¹, and that no heat is lost.

What is the enthalpy change of neutralisation, in kJ per mole of water formed?

Question 22

Equilibrium position

Hydrogen can be made by reacting carbon monoxide with steam:

$C O (g) + H_{2} O (g) ⇌ C O_{2} (g) + H_{2} (g) Δ H = - 41 {kJ mol}^{- 1}$

The mixture is at equilibrium in a closed system. Which of the following changes, each made on its own, would increase the equilibrium yield of hydrogen?

1. Increasing the temperature

2. Increasing the total pressure

3. Adding more steam

Question 23

Electrolysis calculations

Aqueous copper(II) sulfate is electrolysed using inert electrodes. Copper is deposited at the cathode and oxygen is given off at the anode.

By the time 0.32 g of copper has been deposited, what volume of oxygen, measured at room temperature and pressure, has been given off?

(Relative atomic mass: Cu = 64. One mole of any gas occupies 24 dm³ at room temperature and pressure.)

Question 24

Alkenes, isomers and cracking

Which of the following statements about but-1-ene, $C H_{2} = C H C H_{2} C H_{3}$ , is/are correct?

1. It is a structural isomer of 2-methylpropene, $(C H_{3})_{2} C = C H_{2}$ .

2. It reacts with bromine, $B r_{2}$ , to form 1,2-dibromobutane.

3. It can be formed, together with ethane, when hexane is cracked.

Question 25

Carboxylic acids and their salts

Propanoic acid, $C H_{3} C H_{2} C O O H$ , reacts with calcium carbonate to form a salt, carbon dioxide and water.

Which option gives the formula of the salt and the number of moles of propanoic acid that react with one mole of calcium carbonate?

Question 26

Condensation polymers

A polyamide is made by condensation polymerisation of hexane-1,6-diamine, $H_{2} N (C H_{2})_{6} N H_{2}$ , with hexanedioic acid, $H O O C (C H_{2})_{4} C O O H$ . The repeating unit of the polymer contains one unit from each monomer.

What is the relative formula mass of the repeating unit?

(Relative formula masses: hexane-1,6-diamine = 116, hexanedioic acid = 146, water = 18)

Question 27

Air, pollution and water treatment

Which of the following statements is/are correct?

1. Fluoride ions are added to drinking water to kill harmful microorganisms.

2. Nitrogen oxides form in petrol engines when nitrogen and oxygen from the air react at high temperature.

3. Argon makes up about 1% of dry air by volume.

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