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IGCSE Chemistry 0620 Paper 3 Practice Paper (Core Theory) — 80 marks, 1 hour 15 minutes, answers and marking scheme
IGCSE Chemistry practice – Core
An original practice paper written to the Cambridge IGCSE Chemistry 0620 Paper 3 format: Core level, 6 structured questions, 33 parts, 80 marks and 1 hour 15 minutes. All questions are original and are not past paper questions or an official mark scheme.
Paper at a glance
| Paper | Level | Time | Marks |
|---|---|---|---|
| Paper 3 | Core | 1 hour 15 minutes | 80 marks |
Questions
Total: 80 marks · 1 hour 15 minutes · calculator allowed
Question 1 · States of matter and separation [14]
a) Name the change of state from solid to liquid and from gas to liquid. [2]
b) After a perfume bottle is opened, the smell reaches the other side of the room. Explain this in terms of particles, and explain why diffusion is faster at a higher temperature. [3]
c) Rock salt is mixed with sand. Describe the three main steps needed to obtain dry pure salt from rock salt. [3]
d) A 25.0 g impure sample gives 18.0 g of pure sodium chloride. Calculate the percentage purity by mass. [2]
e) A 250 g salt solution contains 12.0% sodium chloride by mass. Calculate the mass of sodium chloride and the mass of water. [2]
f) A laboratory uses melting point to check purity. How does the melting point of a pure substance differ from that of an impure one? [2]
Question 2 · Atomic structure and the Periodic Table [13]
a) Define proton number, mass number and isotope. [3]
b) Chlorine has the isotopes 35/17 Cl and 37/17 Cl. Calculate the number of neutrons in each and explain why they have identical chemical properties. [3]
c) A sample of chlorine contains 75% Cl-35 and 25% Cl-37. Calculate the relative atomic mass of chlorine to one decimal place. [3]
d) Chlorine has proton number 17. Write its electron arrangement and state its group and period. [2]
e) Describe how a chlorine atom forms a chloride ion, and give the ion electron arrangement and charge. [2]
Question 3 · Ionic bonding, acids and salts [14]
a) Using sodium chloride as an example, explain how ionic bonding is formed. [3]
b) Explain why sodium chloride has a high melting point and why only the molten or aqueous form conducts electricity. [2]
c) Write a balanced equation, with state symbols, for the reaction between calcium carbonate and dilute hydrochloric acid. [3]
d) 10.0 g of calcium carbonate reacts completely with excess acid. Calculate the mass of carbon dioxide formed. (M: CaCO3 = 100, CO2 = 44) [2]
e) What volume does that carbon dioxide occupy at room temperature and pressure? (molar volume = 24 dm3 mol-1) [2]
f) Which salt is formed when nitric acid reacts with potassium hydroxide? How can an indicator show that neutralisation is just complete? [2]
Question 4 · Rates of reaction and energy changes [14]
a) State two ways of increasing the rate of reaction between marble chips (calcium carbonate) and dilute hydrochloric acid. [2]
b) Use collision theory to explain why crushing the marble speeds up the reaction. [3]
c) An experiment collects 120 cm3 of gas in 40 s, of which 80 cm3 is collected in the first 20 s. Calculate the average rate overall and the rate over the first 20 s. [3]
d) How would you tell from an experiment that a reaction is exothermic, and is its ΔH positive or negative? [2]
e) A fuel has ΔH = -890 kJ mol-1 for combustion. How much energy is released when 0.050 mol burns completely? [2]
f) State two key points about a catalyst (its effect on rate and what happens to it). [2]
Question 5 · Organic chemistry [13]
a) Give the general formula of the alkanes, the molecular formula of butane, and the homologous series and formula of ethene. [3]
b) Write the balanced equation for the complete combustion of propane. [3]
c) At the same temperature and pressure, what volume of carbon dioxide is formed when 2.0 dm3 of propane burns completely? [2]
d) Ethene is used to make poly(ethene). Name the reaction, give the repeat unit and state the conditions. [3]
e) How could bromine water be used to distinguish ethene from ethane? State the observation. [2]
Question 6 · Air, electrolysis and the environment [12]
a) Give the approximate percentage by volume of nitrogen and of oxygen in dry air. [2]
b) Copper(II) sulfate solution is electrolysed with copper electrodes. Give the cathode reaction, the anode product and the colour change of the solution. [3]
c) Electrolysis deposits 0.50 mol of copper. What mass is this? (M: Cu = 63.5) [2]
d) Explain how burning fossil fuels causes acid rain, and state one effect of acid rain. [3]
e) Give two gas tests: (i) carbon dioxide; (ii) water vapour. [2]
Answers and marking scheme
| Part | Answer | Marking points | Marks |
|---|---|---|---|
| 1a) | melting; condensation. | 1 mark: melting. 1 mark: condensation. |
2 |
| 1b) | Particles move randomly and continuously; perfume particles move from a region of higher concentration to lower concentration (net movement); at higher temperature the average kinetic energy of particles is greater, so they move faster and collide more often, making diffusion faster. | 1 mark: particles move randomly/continuously. 1 mark: net movement from high to low concentration. 1 mark: higher temperature gives greater kinetic energy, so faster motion (more frequent collisions). |
3 |
| 1c) | Add water to dissolve the salt; filter to remove the insoluble sand; evaporate the filtrate to crystallisation (then dry the crystals). | 1 mark: add water to dissolve the salt. 1 mark: filter off the insoluble sand. 1 mark: evaporate/crystallise the filtrate. |
3 |
| 1d) | 18.0 / 25.0 x 100% = 72.0% | 1 mark: 18.0 / 25.0 (= 0.72). 1 mark: x 100% giving 72.0%. |
2 |
| 1e) | sodium chloride = 250 x 0.120 = 30.0 g; water = 250 – 30.0 = 220 g | 1 mark: 30.0 g of sodium chloride. 1 mark: 220 g of water. |
2 |
| 1f) | A pure substance melts at a sharp, fixed temperature; an impure substance melts at a lower temperature over a wider range. | 1 mark: pure substance melts at a fixed temperature (narrow range). 1 mark: impurities lower the melting point and widen the range. |
2 |
| 2a) | Proton number is the number of protons in the nucleus; mass number is the number of protons plus neutrons; isotopes are atoms of the same element with the same proton number but different numbers of neutrons. | 1 mark: proton number = number of protons. 1 mark: mass number = protons + neutrons. 1 mark: isotopes = same protons, different neutrons. |
3 |
| 2b) | neutrons = 35 – 17 = 18 and 37 – 17 = 20; both have 17 protons and therefore the same electron arrangement, so their chemical properties are the same. | 1 mark: 18 neutrons. 1 mark: 20 neutrons. 1 mark: identical electron arrangement, so identical chemical properties. |
3 |
| 2c) | (0.75 x 35) + (0.25 x 37) = 26.25 + 9.25 = 35.5 | 1 mark: 26.25. 1 mark: 9.25. 1 mark: total 35.5 (no unit). |
3 |
| 2d) | electron arrangement 2,8,7; group 7 (VII), period 3. | 1 mark: 2,8,7. 1 mark: group 7, period 3. |
2 |
| 2e) | a chlorine atom gains one electron to form Cl-, arrangement 2,8,8 (same as argon), charge -1. | 1 mark: gains one electron, arrangement 2,8,8. 1 mark: Cl- with a charge of -1. |
2 |
| 3a) | a sodium atom loses one electron to form Na+ (2,8); a chlorine atom gains that electron to form Cl- (2,8,8); the electrostatic attraction between Na+ and Cl- is the ionic bond. | 1 mark: Na loses one electron to form Na+. 1 mark: Cl gains one electron to form Cl-. 1 mark: electrostatic attraction between oppositely charged ions. |
3 |
| 3b) | strong electrostatic attraction between ions means much energy is needed to break the lattice; in the solid the ions are held in fixed positions, but when molten or dissolved the ions are free to move. | 1 mark: strong ionic attraction gives a high melting point. 1 mark: ions fixed in solid, free to move when molten or aqueous. |
2 |
| 3c) | CaCO3(s) + 2HCl(aq) -> CaCl2(aq) + H2O(l) + CO2(g) | 1 mark: correct reactants (2HCl). 1 mark: all three products. 1 mark: all state symbols correct. |
3 |
| 3d) | n(CaCO3) = 10.0 / 100 = 0.100 mol; n(CO2) = 0.100 mol; m = 0.100 x 44 = 4.40 g | 1 mark: 0.100 mol CaCO3 (1:1 ratio). 1 mark: 4.40 g of CO2. |
2 |
| 3e) | 0.100 x 24 = 2.4 dm3 (2,400 cm3) | 1 mark: 0.100 x 24. 1 mark: 2.4 dm3. |
2 |
| 3f) | potassium nitrate (KNO3); with universal indicator the colour turns green at pH 7, showing exact neutralisation. | 1 mark: potassium nitrate, KNO3. 1 mark: indicator turns green at pH 7. |
2 |
| 4a) | raise the temperature; crush the marble chips to increase surface area (or use more concentrated acid). | 1 mark: higher temperature. 1 mark: larger surface area (or higher concentration). |
2 |
| 4b) | crushing increases the surface area in contact with the acid; more collisions per second; more of these collisions have energy at least equal to the activation energy, so the rate increases. | 1 mark: larger surface area. 1 mark: more collisions per second. 1 mark: more collisions exceed the activation energy, so rate rises. |
3 |
| 4c) | overall: 120 / 40 = 3.0 cm3 s-1; first 20 s: 80 / 20 = 4.0 cm3 s-1 | 1 mark: 3.0 cm3 s-1. 1 mark: 4.0 cm3 s-1. 1 mark: correct units on both answers. |
3 |
| 4d) | the thermometer reading rises (the mixture gets hotter); ΔH is negative. | 1 mark: temperature rises. 1 mark: ΔH is negative. |
2 |
| 4e) | 0.050 x 890 = 44.5 kJ | 1 mark: 0.050 x 890. 1 mark: 44.5 kJ. |
2 |
| 4f) | a catalyst provides an alternative route of lower activation energy, so the rate increases; its mass and chemical properties are unchanged at the end (it is not used up). | 1 mark: lower activation energy route, faster rate. 1 mark: unchanged in mass and chemical properties at the end. |
2 |
| 5a) | alkanes: CnH2n+2; butane: C4H10; ethene belongs to the alkenes, C2H4. | 1 mark: CnH2n+2. 1 mark: C4H10. 1 mark: alkene, C2H4. |
3 |
| 5b) | C3H8 + 5O2 -> 3CO2 + 4H2O | 1 mark: C3H8 + 5O2. 1 mark: 3CO2 + 4H2O. 1 mark: all atoms balanced. |
3 |
| 5c) | volume ratio = mole ratio = 1 : 3, so 2.0 x 3 = 6.0 dm3 | 1 mark: volume ratio 1:3. 1 mark: 6.0 dm3. |
2 |
| 5d) | addition polymerisation; repeat unit -CH2-CH2-; conditions: high pressure (about 200 atm), about 200 C, with a catalyst. | 1 mark: addition polymerisation. 1 mark: repeat unit -CH2-CH2-. 1 mark: high pressure and a catalyst (about 200 C). |
3 |
| 5e) | bubble each gas through orange bromine water: ethene decolourises it (addition reaction), ethane does not. | 1 mark: ethene decolourises bromine water. 1 mark: ethane leaves it orange. |
2 |
| 6a) | nitrogen about 78%; oxygen about 21%. | 1 mark: nitrogen 78%. 1 mark: oxygen 21%. |
2 |
| 6b) | cathode: Cu2+ + 2e- -> Cu (red-brown copper deposited); anode: oxygen gas; the blue colour fades as Cu2+ is removed. | 1 mark: cathode Cu2+ + 2e- -> Cu. 1 mark: oxygen at the anode. 1 mark: blue colour fades. |
3 |
| 6c) | 0.50 x 63.5 = 31.75 g | 1 mark: 0.50 x 63.5. 1 mark: 31.75 g. |
2 |
| 6d) | fossil fuels contain sulfur compounds and hot engines also oxidise nitrogen: burning produces SO2 and NOx; SO2 dissolves in rain to form sulfurous/sulfuric acid, giving rain with pH below 5.6; acid rain corrodes limestone and metal structures (or acidifies lakes and damages trees). | 1 mark: burning produces SO2 (and NOx). 1 mark: SO2 dissolves in rain to form acid. 1 mark: one specific effect (corrosion, acidified lakes, damaged trees). |
3 |
| 6e) | carbon dioxide turns limewater milky/cloudy; water vapour turns white anhydrous copper(II) sulfate blue. | 1 mark: limewater turns milky. 1 mark: anhydrous copper(II) sulfate turns from white to blue. |
2 |
Timing plan
| Section | Suggested time | Marks |
|---|---|---|
| Questions 1-2 | 24 min | 27 marks |
| Questions 3-4 | 26 min | 28 marks |
| Questions 5-6 | 25 min | 25 marks |
| Checking | remaining time | – |
Common pitfalls
- Calculations with the answer only and no mole working lose every method mark.
- Unbalanced equations or missing state symbols lose marks item by item.
- Explanations that list key words without a cause-and-effect sentence.
- Mole answers given without units: g, dm3, mol dm-3.
Frequently asked questions
Who is this paper for?
Students preparing for IGCSE Chemistry 0620 Core papers (Paper 1 and Paper 3), especially those who need practice with mole calculations and balanced equations.
Does the answer booklet include a mark scheme?
Yes. All 33 parts list their marking points so you can mark yourself or a tutor can mark point by point.
Can I print it?
Yes, both the question paper and the answer booklet are A4 PDFs ready to print.
Originality statement: every question, data set and context in this paper was written by TutorZone. It is not a Cambridge IGCSE Chemistry 0620 past paper or an official mark scheme.
This paper is not an IGCSE Chemistry 0620 past paper; only the structure and mark distribution follow the official Paper 3 (Core) format.
