Q4 Exam Questions

Question 1

Define (i) atomic number, (ii) mass number

Answer 1

Atomic number = number of protons in the nucleus of an atom.
Mass number = number of protons and neutrons in the nucleus of an atom.

Question 2

Taking the valency of gallium (Ga) as 3, write the formula for the simplest compound formed from (i) gallium and nitrogen, (ii) gallium and oxygen.

Answer 2

Gallium and nitrogen = GaN
Gallium and oxygen = Ga2O3

Question 3

Predict the two possible shapes of a molecule AB, where n = 2

Answer 3

V-shape

Question 4

Identify the energy change associated with the following balanced equation: X+ (g) —> X2+ (g) + e-

Answer 4

Second ionisation energy

Question 5

What is diffusion?

Answer 5

The spreading of molecules from an area of high concentration to low concentration.

Question 6

Stage 2 and 4 of mass spectrometry

Answer 6

2 = ionisation
4 = separation

Question 7

A laboratory technician diluted 25.0 cm^3 of a 0.12 M solution to 30.0 cm^3 by adding deionised water. Find the new concentration of the solution in moles per litre.

Answer 7

25x0.12/30 = 0.1M

Question 8

What is an enzyme?

Answer 8

A biological catalyst that alters the rate of a reaction.

Question 9

Draw a structure of propane-1,2,3-triol (glycerol) to show al of its atoms and al of its bonds.

Answer 9

| |
H-C-C-C-H
| | |
OH OH OH

Question 10

The set of elements {Li, Na, K} is one of Dobereiner’s triads. Refer to this example to explain Dobereiner’s contribution to the development of the periodic table.

Answer 10

Li, Na, and K groups all have similar chemical properties.
The atomic mass of Na is the average of Li and K.

Question 11

Why is a photon emitted as the electron moves from one energy level to another as shown?

Answer 11

The electron in the outer shell has more energy/in an excited state.

Question 12

Why is the second ionisation energy of lithium significantly larger than its first?

Answer 12

The second electron comes from the shell that is closer to the nucleus.

Question 13

What colour is observed in a flame test on a salt of (i)lithium, (ii) copper?

Answer 13

Lithium = red
Copper = blue/green

Question 14

State Avogadro’s Law

Answer 14

Equal volumes of all gases, at the same temperature and pressure, have the same number of molecules.

Question 15

One of the largest diamonds ever mined was found in Botswana in June 2021. The diamond had a mass of 1098 carats and contained exactly 18.3 moles of carbon. Assuming this stone contained only carbon, calculate the mass of one carat expressed in grams.

Answer 15

18.3x12(carbon) = 219.6g of Carbon in 1098 carats
One carat = 219.6/1098 = 0.200g

Question 16

What reagents are used to confirm the presence of nitrate ions in an aqueous solution?

Answer 16

Iron (III) sulfate

Question 17

Which one ofthe following four compounds would you expect to have the strongest carbon to carbon bonding: ethane, ethene, ethyne, benzene?

Answer 17

Ethyne

Question 18

The structure of aspirin is shown. Calculate the average daily dose (in mg) when a person took a total of 0.146 moles of ‘low dose’ aspirin over 365 days.

Answer 18

Aspirin = C9H8O4, Mr = 180
0.146x180 = 26.280g aspirin in 365 days
26.28/365 = 0.0720g per day
0.0720x1000 = 72.0mg per day

Question 19

Draw a labelled diagram of Thompsons plum pudding model of the atom

Question 20

The diagram represents the 10 electrons in the 4s and 3d sub-levels of a neutral atom of a certain element in its ground state. What is the element?

Answer 20

Nickel

Question 21

What isotope is produced when the nucleus of an 241/95Am atom releases an alpha particle?

Answer 21

Neptunium237

Question 22

Write the chemical formulae for: (i) magnesium sulfite, (ii) copper(ll) oxide.

Answer 22

Magnesium sulfite = MgSO3
Copper (III) oxide = CuO

Question 23

Give two possible shapes of a covalent molecule with the general formula QX3

Answer 23

Trigonal

Question 24

Each of the small metal canisters shown in the photograph contains 0.36 moles of carbon dioxide. The contents of one canister were released into a flat bicycle tube.
The gas inflated the tube to a volume of 1.0x 103 m3ata temperature of 293 K. Calculate the pressure of the gas inside the tube correct to two significant figures.

Question 25

How can a catalyst lower the activation energy of a reaction?

Answer 25

Provides an alternative pathway for the reaction

Question 26

Under what circumstances do ionic compounds conduct electricity?

Answer 26

In aqueous solution / dissolved in water

Question 27

Copy into your answerbook the structure of vanillin, the main component of the extract of the vanilla bean.
(i) Circle the aldehyde group.
(ii) Write the molecular formula for vanillin.

Answer 27

Circle CHO group
C8H8O3

Question 28

What are cathode rays?

Answer 28

Beams of electrons

Question 29

Bananas contain small quantities of potassium-40, a radioactive isotope. What is the daughter nucleus when K-40 emits an electron in beta decay?

Answer 29

Calcium 40

Question 30

State Avogadro’s Law (again)

Answer 30

Equal volumes of all gases, at the same temperature and pressure, have the same number of molecules.

Question 31

Give two differences between a sigma and a pi covalent bond.

Answer 31

Sigma = determines the shape of a molecule, formed from head-on overlap of orbitals.
Pi = does not determine the shape of a molecule, formed from the sideways overlap of orbitals.

Question 32

The structure of ibuprofen is shown. Ibuprofen is the active ingredient in many fever and pain-relief suspensions given to children. A single 5 cm^3 dose, suitable for children aged 1 to 3 years, contains 4.86 x 107 moles of ibuprofen.
How many milligrams of ibuprofen are in this single dose?