Cambridge IGCSE Chemistry - 0620 - Core Paper 3 2024 Summer Zone 3

1. Fig. 1.1 shows the structures of seven substances, A, B, C, D, E, F, and G.
[Image_1: Chemical structures of substances A, B, C, D, E, F, G]
(a) Answer the following questions using only the structures in Fig. 1.1. Each structure may be used once, more than once or not at all. State which structure represents:
(i) a compound that is the main constituent of natural gas [1]
(ii) the monomer used to produce poly(ethene) [1]
(iii) a giant covalent structure [1]
(iv) a compound that has a high melting point [1]
(v) a waste gas from digestion in animals [1]
(vi) a solid at room temperature that conducts electricity when dissolved in water [1]
(b) Complete Fig. 1.2 to show the dot-and-cross diagram for structure B. Show the outer electron shells only.
[Image_2: Dot-and-cross diagram] [2]

2. (a) Intracellular fluid is the solution between the cells in the human body. Table 2.1 shows the masses, in mg, of some ions in 100cm³ of intracellular fluid.
[Table_1: Ions in intracellular fluid]
Answer these questions using information from Table 2.1:
(i) Name the positive ion that is present in the lowest concentration. [1]
(ii) Name the ion that contains an element in Group IV of the Periodic Table. [1]
(b) Describe a test for sulfate ions.
test
observations [2]
(c) Small amounts of ammonium ions and chloride ions are formed in some cells of the body. State the formula of the compound formed from ammonium ions and chloride ions. [1]
(d) Choose from the list the salt that is insoluble in water. Tick (✓) one box. [1]
copper(II) nitrate
lead(II) chloride
potassium nitrate
sodium chloride
(e) Table 2.2 shows some properties of the Group I metals.
[Table_2: Properties of Group I metals]
Use the information in Table 2.2 to:
• predict the hardness of potassium
• describe the observations when rubidium reacts with water. [2]
(f) Sodium reacts with hydrogen to produce sodium hydride, NaH. Complete the symbol equation for this reaction. 2Na + ........ → .....NaH [2]

3. (a) Molten calcium bromide is electrolysed.
(i) Define the term electrolysis. [2]
(ii) Name an inert metal that can be used for the electrodes. [1]
(iii) Name the product formed at each electrode.
positive electrode
negative electrode [2]
(b) Calcium reacts with water. An alkaline solution is produced.
(i) Name the ion which causes a solution to be alkaline. [1]
(ii) Choose the pH value of an alkaline solution. Draw a circle around your chosen answer. pH1 pH5 pH7 pH9 [1]
(iii) Dilute hydrochloric acid is added to a solution of litmus in alkaline solution until the acid is in excess. State the colour change of the litmus. from ............................................................. to ............................................................ [2]
(c) Calcium carbonate is added to the blast furnace in the production of iron. Calcium carbonate breaks down when heated to produce calcium oxide and a gas that turns limewater milky.
(i) Name the gas that turns limewater milky. [1]
(ii) Name the type of chemical reaction that takes place when calcium carbonate is heated. [1]

4. (a) Chlorophyll is a coloured compound found in plants. Chlorophyll is needed for photosynthesis.
(i) Complete the word equation for photosynthesis. carbon dioxide + water → ........................ + ........................ [2]
(ii) State one other condition that is essential for photosynthesis. [1]
(b) Several other coloured compounds are found in plant leaves. A student extracts a mixture of coloured compounds from a plant leaf. Fig. 4.1 shows the apparatus used to separate the coloured compounds.
[Image_3: Apparatus for separating coloured compounds]
(i) Name this method of separation. [1]
(ii) Suggest why the base line is drawn in pencil and not in ink. [1]
(iii) The liquid used to separate the coloured compounds is a solution of methyl ethanoate in ethanoic acid. State the meaning of the term solution. [1]
(c) Fig. 4.2 shows the displayed formula of a compound found in plant cells.
[Image_4: Displayed formula]
On Fig. 4.2, draw a circle around the alcohol functional group. [1]

5. (a) An atom of phosphorus is represented by the symbol shown.
[Image_5: Phosphorus atom symbol]
Describe this atom of phosphorus in terms of:
• the position of the electrons, neutrons and protons in the atom
• the number of neutrons and the number of protons
• the electronic configuration. [5]
(b) Complete the symbol equation for the reaction of phosphorus with oxygen. .....P + .....O₂ → P₄O₁₀ [2]
(c) Fig. 5.1 shows the displayed formula of a compound of phosphorus.
[Image_6: Displayed formula]
Deduce the molecular formula of this compound. [1]
(d) Another compound of phosphorus has the formula Na₃PO₄. Complete Table 5.1 to calculate the relative formula mass of Na₃PO₄.
[Table_3: Relative formula mass calculation]
relative formula mass = .............................. [2]
(e) Phosphates in rivers can cause deoxygenation of water. State one source of phosphates in river water. [1]

6. Dilute hydrochloric acid reacts with small pieces of calcium carbonate. 2HCl(aq) + CaCO₃(s) → CaCl₂(aq) + H₂O(l) + CO₂(g)
(a) State the meaning of the state symbol (aq). [1]
(b) Fig. 6.1 shows how the mass of small pieces of calcium carbonate changes as the reaction proceeds. The calcium carbonate is in excess.
[Image_7: Graph of reaction progress]
(i) Deduce the mass of calcium carbonate two minutes from the start of the reaction. [1]
(ii) Explain how the graph shows that the calcium carbonate is in excess. [1]
(iii) The experiment is repeated at a higher temperature. All other conditions stay the same. Draw a line on Fig. 6.1 to show how the mass of calcium carbonate changes at a higher temperature as the time increases. [2]
(c) (i) Describe the effect, if any, on the rate of reaction when large pieces of calcium carbonate are used instead of small pieces of calcium carbonate. All other conditions stay the same. [1]
(ii) Increasing the concentration of dilute hydrochloric acid increases the rate of reaction of dilute hydrochloric acid with calcium carbonate. Choose the correct unit of concentration from the list. Draw a circle around your chosen answer. dm³ /g g/dm² mol/dm mol/dm³ [1]
(d) Concentrated hydrochloric acid gives off hydrogen chloride gas. Hydrogen chloride is an acidic gas that turns damp universal indicator paper red. A long glass tube is set up as shown in Fig. 6.2.
[Image_8: Apparatus for hydrogen chloride experiment]
Explain these results in terms of kinetic particle theory. [3]
(e) Hydrogen chloride breaks down to form hydrogen and chlorine at 1500°C. The reaction in endothermic. State the meaning of the term endothermic. [1]

7. Chromium and iron are transition elements. They are ductile and have high melting and boiling points.
(a) State three other physical properties of chromium. [3]
(b) The formula for rust is Fe₂O₃·xH₂O.
(i) State the chemical name of rust. [2]
(ii) An iron object is coated with plastic. Explain how this prevents the iron from rusting. [2]
(c) Chromium behaves as a typical metal when it reacts with sulfuric acid. Complete the word equation for this reaction. chromium + sulfuric acid → ........................ ........................ + ........................ [2]
(d) The list shows five metals.
[Table_4: Metals list]
Put these metals in order of their reactivity. Put the most reactive metal at the top. least reactive most reactive [2]
(e) Zinc can be produced by heating zinc oxide with carbon. ZnO + C → Zn + CO Describe how this equation shows that zinc oxide is reduced. [1]

8. This question is about hydrocarbons.
(a) Table 8.1 shows the names, formulae and boiling points of methane, ethane, propane and butane.
[Table_5: Hydrocarbons boiling points]
Use the information in Table 8.1 to answer these questions:
(i) Name the homologous series that includes methane, ethane, propane and butane. [1]
(ii) State the trend in the boiling point of this homologous series as the number of carbon atoms increases. [1]
(iii) Deduce the general formula of this homologous series. [1]
(b) Complete the word equation for the complete combustion of ethane. ethane + oxygen → ........................ + ........................ ........................ [2]
(c) Long-chain hydrocarbons can be cracked to produce alkenes and hydrogen.
(i) State two conditions for cracking. [2]
(ii) The diesel oil fraction from the fractional distillation of petroleum can be used for cracking. Give one other use of the diesel oil fraction. [1]
(d) Alkene molecules can react together to produce polymers. Define the term polymer. [2]