Question 1

A sample of chlorine gas contains two isotopes: 75% Cl-35 (atomic mass 34.97 u) and 25% Cl-37 (atomic mass 36.97 u). What is the relative atomic mass (A_r) of chlorine in this sample?
Correct answer: 35.50

Accepted Answer

35.50

Question 2

Which of the following best explains why sodium chloride conducts electricity when molten but not when solid?
Correct answer: Ions are free to move in the molten state but fixed in the solid state.

Accepted Answer

Ions are free to move in the molten state but fixed in the solid state.

Question 3

A student is asked to separate a mixture of sand and salt. Which sequence of experimental techniques should be used?
Correct answer: Dissolve in water, filter, evaporate the filtrate.

Accepted Answer

Dissolve in water, filter, evaporate the filtrate.

Question 4

Which statement best describes the difference between ionic and covalent bonding?
Correct answer: Ionic bonding involves transfer of electrons; covalent bonding involves sharing of electrons.

Accepted Answer

Ionic bonding involves transfer of electrons; covalent bonding involves sharing of electrons.

Question 5

Which of the following best explains why diamond has a high melting point and does not conduct electricity?
Correct answer: It has a giant covalent structure with no free electrons.

Accepted Answer

It has a giant covalent structure with no free electrons.

Question 6

A chemical plant releases sulfur dioxide (SO₂) into the atmosphere. Which environmental impact is most directly associated with this emission?
Correct answer: Acid rain formation

Accepted Answer

Acid rain formation

Question 7

A solution of hydrochloric acid (HCl) is titrated with sodium hydroxide (NaOH). Which indicator would be most appropriate for this reaction, and why?
Correct answer: Either phenolphthalein or methyl orange, because both change color sharply at the equivalence point.

Accepted Answer

Either phenolphthalein or methyl orange, because both change color sharply at the equivalence point.

Question 8

Which of the following best describes the process of electrolysis of molten lead(II) bromide (PbBr₂)?
Correct answer: Lead is deposited at the cathode and bromine is released at the anode.

Accepted Answer

Lead is deposited at the cathode and bromine is released at the anode.

Question 9

Which of the following is a correct statement about the trends in the Periodic Table?
Correct answer: Atomic radius decreases across a period from left to right.

Accepted Answer

Atomic radius decreases across a period from left to right.

Question 10

A student is asked to calculate the empirical formula of a compound containing 40% sulfur and 60% oxygen by mass. What is the empirical formula?
Correct answer: SO₃

Accepted Answer

SO₃

Question 11

Which of the following best explains why metals are malleable and conduct electricity?
Correct answer: Metals have a lattice of positive ions surrounded by a sea of delocalized electrons.

Accepted Answer

Metals have a lattice of positive ions surrounded by a sea of delocalized electrons.

Question 12

During a laboratory experiment, a student observes that a white solid forms when solutions of silver nitrate and sodium chloride are mixed. What type of reaction has occurred?
Correct answer: Precipitation

Accepted Answer

Precipitation

Question 13

Which of the following is a correct description of an exothermic reaction?
Correct answer: A reaction that releases heat to the surroundings, causing the temperature to rise.

Accepted Answer

A reaction that releases heat to the surroundings, causing the temperature to rise.

Question 14

A sample of gas is compressed at constant temperature. According to the kinetic particle theory, what happens to the pressure and why?
Correct answer: Pressure increases because particles collide more frequently with the walls.

Accepted Answer

Pressure increases because particles collide more frequently with the walls.

Question 15

Which of the following best describes the role of a catalyst in a chemical reaction?
Correct answer: It lowers the activation energy, increasing the rate of reaction without being consumed.

Accepted Answer

It lowers the activation energy, increasing the rate of reaction without being consumed.

Question 16

A student is asked to design an experiment to determine the effect of concentration on the rate of a reaction. Which variable should be kept constant to ensure a fair test?
Correct answer: Temperature

Accepted Answer

Temperature

Question 17

Which of the following is a correct statement about acids, bases, and salts?
Correct answer: A salt is formed when the hydrogen ion of an acid is replaced by a metal ion or ammonium ion.

Accepted Answer

A salt is formed when the hydrogen ion of an acid is replaced by a metal ion or ammonium ion.

Question 18

Which of the following best explains why carbon monoxide (CO) is dangerous to humans?
Correct answer: It binds to hemoglobin more strongly than oxygen, reducing oxygen transport in the blood.

Accepted Answer

It binds to hemoglobin more strongly than oxygen, reducing oxygen transport in the blood.

Question 19

Which of the following is the best method to obtain pure water from seawater?
Correct answer: Distillation

Accepted Answer

Distillation

Question 20

Which of the following statements about organic compounds is correct?
Correct answer: They contain carbon atoms covalently bonded to other elements.

Accepted Answer

They contain carbon atoms covalently bonded to other elements.

Overview of Cambridge IGCSE Chemistry 0620 Syllabus

Study Guide - Practice Questions

Study Guide - Flashcards