chemistry revision 2025, 2024, 2023 igcse papers

2025 43m/j

what is an alloy-

a mixture of a metal with other elements

Give two observations which show that the zinc carbonate is in excess in -

M1 solid stops dissolving / disappearing M2 no more bubbles / fizzing / effervescence on addition of solid

Step 1 is repeated using large pieces of zinc carbonate instead of powdered zinc carbonate. All other conditions are the same. The rate of reaction decreases. Explain why the rate of reaction decreases. Give your answer in terms of particles

• smaller surface area

• frequency of collisions between particles decreases

hydrated crystals form in step 4. State what is meant by the term hydrated.-

crystals that are chemically bonded with water

THE SULFUR DIOXIDE TO SULFUR TRIOXIDE REACTION IS A ___________________

REVERSE REACTION

rate and yield doesnt become low- they _________

decrease

NEVER EVER EVER SAY BUTANOL OR PROPANOL

ITS ALWAYS BUTAN-1-OL AND PROPAN-1-OL

LIthium added to water- (a solid at room temperature btw)

solid dissolves / disappears • fizzing/ bubbles / effervescence • solid floats • solid moves (on surface)

at room temperature and pressure- chlorine is

CHLORINE IS PALE YELLOW GREEN IN COLOUR and GAS

2025 42 m/j

covalent bond-

a pair of electrons shared by two atoms

Explain, in terms of structure and bonding, why Cl 2O boils at a low temperature and does not thermally decompose into its constituent elements, Cl 2 and O2

• there is weak attraction between molecules and strong covalent bonding between atoms

• therefore, during boiling, at a low temperature (weak) forces of attraction between molecules is broken

• during thermal decomposition, high energy or high temperatures are required to break covalent bonds between Cl2 and O2 atoms

Give two reasons why liquid Cl 2O is a poor conductor of electricity.-

• no ions

• no MOBILE electrons

copper(II) sulfate is what colour (in solution)

BLUE

Electrolysis of aqueous copper(II) sulfate is carried out using the apparatus shown in Fig. 3.1. The electrodes are made of platinum. Describe the change in appearance, if any, of the electrolyte when platinum electrodes are used.

becomes paler blue or becomes colourless

what is the formula of chromite

FeCr2O4

Suggest one disadvantage of extracting chromium by reacting chromite with carbon.

chromium will need to be separated from iron

identify the alkali metal which: (i) has the highest melting point

Lithium

WHY IS SO AND SO UNSATURATED-

it has a carbon-carbon bond which is not a single bond

State one reason why alloys are more useful than pure metals-

harder or stronger

brass contains-

copper + zinc

Bronze contains

copper + tin

Name a substance, other than copper(II) carbonate, that can be added to dilute sulfuric acid to produce aqueous copper(II) sulfate.-

since copper carbonate is insoluble- name an insoluble copper compound (AND IF YOU DONT KNOW ONE PLEASE STUDY THE DAMN NOTES)

remember to show in equations that haber’s process and contact process are reversible

also remember the symbol

iodine is _______ colour at room temperature

grey-black

2025 f/m

State what is meant by the term ionic bond.-

• Strong electrostatic attraction between ions of opposite charge

in a closed system-

no reactants or products can enter or leave

State what the symbol ΔH represents.

enthalpy change- overall energy change

State which other property of manganese is shown by the formation of several oxides

variable oxidation state

reducing agent-

a substance that reduces another substance and is itself oxidised

Explain, in terms of collision theory, why decreasing the temperature decreases the rate of this reaction.

• kinetic energy of particles decreases

• frequency of collisions between particles decreases

• Fewer of the collisions / particles have energy greater than / equal to activation energy

2024 o/n 43

State the meaning of the term amphoteric.

reacts with acids and with bases to produce a salt and water

Tin is a metal that forms both covalent and ionic compounds. Suggest why this is unusual for a metal.

metals form ionic compounds or ionic bonds only OR covalent compounds contain non-metals only

Tin(II) oxide, SnO, is ionically bonded. The melting points of SnCl 4 and SnO are shown in Table 3.1. Table 3.1 melting point/°C SnCl 4 –33 SnO 1080 Explain, in terms of structure and bonding, why SnCl 4 has a much lower melting point than SnO.

• attraction between molecules or intermolecular forces in tin(IV) chloride

• tin(II) oxide has a giant ionic structure

• M3 weaker attraction (between particles) in tin(IV) chloride ORA

When aluminium foil is added to aqueous tin(II) sulfate, a reaction does not occur even though aluminium is above tin in the reactivity series. Explain why a reaction does not occur.

unreactive coating of aluminium oxide (side question- have you memorised the reactivity table??)

State what is meant by the term hydrated.

substance that is chemically combined with water OR containing water of crystallisation

do you know the colour changes of all the indicators

IF NOT PLEASE GO STUDY IT

Suggest why universal indicator is not used for this titration

too many colour changes

A student is provided with an aqueous solution of sodium sulfate. Describe how to prepare a pure sample of sodium sulfate crystals from this solution

• heat the solution / warm the solution /boil the solution / leave solution in hot place

• to saturation (point)/ crystallisation point AND leave to cool

• suitable method of drying

0.325g of Zn is added to dilute sulfuric acid which contains 0.0100 moles of H2SO4 . The equation for this reaction is shown. Zn + H2SO4 → ZnSO4 + H2 (i) Determine whether Zn or H2SO4 is the limiting reactant. Explain your answer

M1 moles of Zn = 0.005 / 5  10–3  (mol),, ,,Zn is limiting because moles of H2SO4 is greater than moles of Zn AND 1:1 ratio required for reaction

In another experiment, 48.0cm3 of hydrogen gas, H2 , is produced. The experiment is carried out at room temperature and pressure, r.t.p. Calculate the number of molecules in 48.0cm3 of H2 gas measured at r.t.p. The value of the Avogadro constant is 6.02 × 1023 .

M1 (48.0 ÷ 24 000 =) 0.00200 (mol) M2 1.20  1021 (molecules) 

After a certain time the reaction stops. Explain why the reaction stops.

____________ is used up

Suggest why it is not possible to use the results in Table 5.1 to determine the exact time when the reaction stops.

time intervals are too large

Explain why the method shown in Fig. 5.3 will not allow the reaction to reach equilibrium

not a closed system

State the meaning of the term hydrocarbon

compound containing carbon and hydrogen only

2024 o/n 42

types of functional groups used in condensation polymerisation

dicarboxylic acid, diol and diamine…… polyesters contains- dicarboxylic acid and diol……. polyamides contains dicarboxylic acid and diamine

when condensation polymer, make sure that the inside the block of each monomer has a different design

State the source of the large alkane molecules used in cracking

petroleum (may close attention to the spelling)

Suggest the type of chemical reaction which happens during cracking.

Thermal decomposition

S2Cl 2 (g) + Cl 2 (g) (symbol of reverse reaction) 2SCl 2 (g) (forward reaction is exothermic)

M1 increases M2 no change M3 increases M4 increases M5 increases

what is activation energy?-

the minimum energy that colliding particle must have to react

State why aluminium is used in food containers

aluminium is resistant to corrosion

2024 o/n 41

Suggest why these two isotopes have identical chemical properties.

• same number of electrons

• same electronic configuration

Write the formula of hydrated copper(II) sulfate

CuSO4•5H2O

Describe what is seen at the cathode during the electrolysis of aqueous copper(II) sulfate.

pink AND solid

State two differences seen if the electrolysis is repeated using copper electrodes instead of graphite electrodes. (the electrolyte est copper sulfate)

• colour remains constant • no bubbles at the anode • anode dissolves

advantages and disadvantages of hydrogen fuel cell instead of gasoline in vehicle engines.

advantages- • water is the only product • no carbon dioxide produced • more efficient

disadvantages- • hydrogen needs to be stored at high pressure • hydrogen hard to store • heavy tanks needed to store hydrogen • fewer (hydrogen) filling stations • less efficient

Organic compounds contain hydrogen atoms. Calculate the number of hydrogen atoms in 44.0g of the ester methyl propanoate, CH3CH2COOCH3 . One mole of CH3CH2COOCH3 contains 6.02 × 1023 molecules. Give your answer in standard form.

M1 Mr of CH3CH2COOCH3 = 88 M2 mol of CH3CH2COOCH3 = 44 / 88 = 0.5 M3 mol of H = 0.5    8 = 4.0 M4 no of H atoms = 4.0    6.02    1023 = 2.408    1024

retention factor formula

M1 distance travelled by substance/ distance travelled by solvent

Explain why the baseline is drawn in pencil

pencil is insoluble (in solvent)

Explain why in Fig. 6.6 only two spots are seen from the mixture of three amino acids.

same Rf value

Suggest how the experiment can be changed to separate all three amino acids.

use a different solvent

2024 m/j 43

process used to produce ammonia from nitrogen

haber’s process

process used to produce ethanol from ethene

catalytic addition

titration

determine the volume of an acid required to neutralise a given volume of an alkali.

Name the reducing agent in the extraction of iron in the blast furnace

carbon monoxide

Explain, in terms of electrons, why magnesium is used for sacrificial protection

1 magnesium loses electrons more readily than / in preference to / instead of iron M2 magnesium is more reactive than iron

2024 o/n 42

why is nitrogen dioxide toxic?

responsible for both acid rain and photochemical smog

what is converted to what in a catalytic converter

• nitrogen dioxide is converted to nitrogen

• carbon monoxide is converted into carbon dioxide

a major component of stainless steel. (you should know all the components)

iron

what is the colour of iron sulfate, magnesium sulfate, copper sulfate (all are aqueous)

green, colourless, blue

Name the gas formed when strontium is added to cold water.

hydrogen

Name the alkaline solution formed when strontium is added to cold water

strontium hydroxide

One Group II metal reacts very slowly when placed in cold water. When heated, the metal reacts with steam to form a white solid. Identify this metal and name the white solid formed.

metal- magnesium, white solid- magnesium oxide

Under certain conditions, iron will react with steam to form an oxide of iron with the formula Fe3O4 . Fe3O4 reacts with dilute hydrochloric acid to form a mixture of iron(II) and iron(III) salts and water. Deduce the symbol equation for the reaction between Fe3O4 and dilute hydrochloric acid

Fe3O4 + 8HCl → 2FeCl3 + FeCl2 + 4H2O

Calculate the volume of ammonia, NH3 , measured at room temperature and pressure, which forms when 1.12g of CaO is heated with excess NH4Cl. [Mr : CaO, 56

M1 mol CaO = 1.12 / 56 = 0.02(00) M2 mol NH3 = M1  2 = 0.02(00)  2 = 0.04(00) M3 vol NH3 = M2  24000 = 0.04  24000 = 960

State why MgS has a high melting point

ionic bonds are strong

State two essential conditions needed for photosynthesis to happen

M1 energy from light M2 presence of chlorophyll

2025 m/j 41

obtain water from aqueous sodium chloride- __________ while, obtain sodium chloride from aqueous sodium chloride- ___________

distillation, crystallisation

Explain in terms of structure and bonding why sodium fluoride has a much higher melting point than fluorine

M1 ionic bonds in NaF(1) M2 attraction between molecules or intermolecular forces in F2(1) M3 weaker attraction (between particles) in F2 ORA (1)

Suggest why the colour of the mixture of gases turns darker purple

iodine particles or molecules (forced) closer together OR same number of iodine particles or molecules in a smaller volume

State the effect that a catalyst has on the activation energy, Ea, of a reaction.

the activation energy is lower

substance that is added at the top of the blast furnace.

calcium chloride (study blast furnace if u havent already)

Name the substance that leaves the blast furnace at A

(molten) iron

Slag is produced from an impurity in iron ore. Name the impurity in iron ore that is converted into slag

silicon(IV) oxide OR silicon dioxide

Name two substances that react together to produce the high temperature in the blast furnace.

coke or carbon and oxygen

Name two waste gases that leave the blast furnace.

nitrogen  carbon dioxide  argon

Suggest why the zinc produced inside the furnace is a gas.

the temperature in the furnace is above or higher than the boiling point of zinc ORA OR the boiling point of zinc is below or less than the temperature of the furnace ORA

Name the process used to coat iron with zinc as a method of rust prevention.

galvanising

State the general name given to oxides that neutralise both acids and bases

amphoteric

24 f/m 42

State the purpose of the combustion of carbon in the blast furnace-

to provide heat