CIE iGCSE Co-Ordinated Science C7.3 Preparation of salts Exam Style Questions Paper 3
Question
(a) Choose from the following substances to answer the questions.
Each substance may be used once, more than once or not at all.
(i) Used as a chemical test for water.
(ii) Used as a solvent.
(iii) Used in aircraft parts.
(iv) Used in the manufacture of sulfuric acid.
(v) Used in the treatment of the water supply.
(vi) Used in the treatment of acidic soil.
(b) Sulfuric acid has the formula H$_{2}$SO$_{4}$.
(i) State the total number of atoms in one molecule of sulfuric acid.
(ii) State the total number of different elements found in one molecule of sulfuric acid.
(c) A student reacts magnesium with dilute sulfuric acid.
The equation for the reaction is shown.
Mg(s) + H$_{2}$SO$_{4}$(aq) MgSO$_{4}$(aq) + H$_{2}$(g)
(i) State the names of the two products of the reaction.
(ii) State the separation technique used by the student to remove any unreacted solid magnesium from the reaction mixture.
▶️Answer/Explanation
Ans : 2(a)(i) copper sulfate ;
2(a)(ii) ethanol ;
2(a)(iii) aluminium ;
2(a)(iv) sulfur ;
2(a)(v) chlorine ;
2(a)(vi) limestone ;
2(b)(i) 7 ;
2(b)(ii) 3 ;
2(c)(i) magnesium sulfate ;
hydrogen ;
2(c)(ii) filtration ;
Question
(a) The list gives the names of six compounds.
aluminium oxide
ammonium nitrate
carbon dioxide
lead bromide
sodium chloride
sulfur dioxide
Answer the questions about these compounds.
Each compound may be used once, more than once or not at all.
State which compound:
(i) has the formula PbBr2.
(ii) is a salt from which ammonia can be displaced.
(iii) is an acidic oxide.
(iv) is a greenhouse gas.
(v) is the main constituent of bauxite.
(b) Aluminium, copper and iron are all solid metals.
State three general physical properties of solid metals.
1 …………………………………………………………………………
2 …………………………………………………………………………
3 …………………………………………………………………………
(c) (i) Duralumin is an alloy of aluminium.
Table 2.1 shows the percentage composition of duralumin.
Calculate the mass of aluminium in 20 kg of duralumin.
mass of aluminium = ……………………………………………. kg
(ii) Table 2.2 shows the melting points of aluminium, copper, magnesium and duralumin.
Duralumin does not have a precise melting point but melts over a range of temperatures.
Explain why duralumin does not have a precise melting point.
▶️Answer/Explanation
Ans : 2(a)(i) lead bromide ;
2(a)(ii) ammonium nitrate ;
2(a)(iii) carbon dioxide / sulfur dioxide ;
2(a)(iv) carbon dioxide ;
2(a)(v) aluminium oxide ;
2(b) any three from:
conducts heat ;
conducts electricity ;
malleable ;
high melting/boiling point ;
2(c)(i) 95 / 100 × 20 = 19 (kg) ;
2(c)(ii) because it is not a pure substance / it is a mixture ;
Question
(a) Five words are shown in the boxes on the left. Five descriptions are shown in the boxes on the right.
Draw one straight line from each word to its correct description.
(b) A student investigates the reaction between calcium carbonate and dilute hydrochloric acid.
Fig. 2.1 shows the apparatus the student uses.
A salt solution and carbon dioxide are made. The carbon dioxide gas is collected in apparatus A.
(i) State the name of apparatus A shown in Fig. 2.1.
…………………………………………………………………………………………………………………….
(ii) State the name of the salt made.
…………………………………………………………………………………………………………………….
(iii) State the chemical test for carbon dioxide. Include the observation for a positive result.
test ……………………………………………………………………………………………………………………
observation …………………………………………………………………………………………………………
(iv) It takes 50 seconds to collect 90cm$^{3}$ of carbon dioxide gas.
Calculate the rate at which carbon dioxide is made in cm$^{3}$/s.
rate = ………………………………………. cm$^{3}$/ s
(v) State two changes to the reaction conditions that reduce the rate of reaction.
1 ……………………………………………………………………………………………………………………….
2 ……………………………………………………………………………………………………………………….
(vi) Calcium carbonate has the formula CaCO$_{3}$.
State the number of different elements present in calcium carbonate.
…………………………………………………………………………………………………………………….
▶️Answer/Explanation
Ans: 2(a)
1 correct 1 mark ;
2 correct 2 marks ;
3 or 4 correct 3 marks ;
5 correct 4 marks ;
2(b)(i) measuring cylinder ;
2(b)(ii) calcium chloride ;
2(b)(iii) (bubble the gas through) lime water ;
goes milky / cloudy ;
2(b)(iv) 1.8 (cm$^{3}$/ s) ;
2(b)(v) any two from:
lower temperature (of acid) ;
lower concentration of acid ;
decrease surface area ;
2(b)(vi) 3 ;
Question
Fig. 11.1 shows the apparatus and reagents used to make a salt.
(a) (i) State the name of process A shown in Fig. 11.1. (Sub-topic – C7.3)
▶️Answer/Explanation
filtration
Explanation: Process A is filtration, which is used to separate solid particles from a liquid.
(ii) State the name of the salt made in this experiment. (Sub-topic – C7.3)
▶️Answer/Explanation
copper sulfate
Explanation: The salt made in this experiment is copper sulfate.
(iii) Carbon dioxide gas is also made.
Explain why the bonds between the carbon atoms and the oxygen atoms in carbon dioxide are covalent. (Sub-topic – C2.5)
▶️Answer/Explanation
two non-metals bonding / electrons are shared
Explanation: The bonds between carbon and oxygen in carbon dioxide are covalent because they involve the sharing of electrons between the carbon and oxygen atoms. Carbon dioxide is a molecule formed by two non-metals (carbon and oxygen), and non-metals typically form covalent bonds by sharing electrons to achieve a stable electron configuration.
(iv) The temperature of the reacting mixture increases during the reaction.
State the name given to all chemical reactions that release heat. (Sub-topic – C5.1)
▶️Answer/Explanation
exothermic
Explanation: Chemical reactions that release heat are called exothermic reactions.
(v) The experiment is repeated using large pieces of copper carbonate instead of powdered copper carbonate.
State what happens to the rate of reaction. (Sub-topic – C6.2)
▶️Answer/Explanation
(rate of reaction) decreases
Explanation: Using large pieces of copper carbonate instead of powdered copper carbonate decreases the rate of reaction. This is because the surface area of the reactant is reduced, leading to fewer collisions between reactant particles per unit time.
(b) Copper carbonate is green. Copper is a transition metal.
State two other properties of transition metals which are not properties of all metals. (Sub-topic – C8.4)
▶️Answer/Explanation
1. high density; 2. catalyst; 3. variable valency (any two)
Explanation:
Two other properties of transition metals are:
- They form colored compounds.
- They can act as catalysts in chemical reactions.
(c) Brass is a mixture containing copper and zinc.
(i) State the name given to a mixture of metals. (Sub-topic – C9.3)
▶️Answer/Explanation
alloy
Explanation: A mixture of metals is called an alloy.
(ii) State one advantage of brass compared to copper. (Sub-topic – C9.3)
▶️Answer/Explanation
stronger / any valid point
Explanation: One advantage of brass compared to copper is that it is stronger and more resistant to corrosion.