CIE iGCSE Co-Ordinated Science C5.1 Exothermic and endothermic reactions Exam Style Questions Paper 3
Question
(a) The proton numbers and nucleon numbers of carbon and hydrogen are shown in Table 11.1
i) State the number of neutrons in a carbon atom and the number of neutrons in a hydrogen atom.
(ii) State the number of electrons in a carbon atom.
(b) (i) State the difference between a saturated hydrocarbon and an unsaturated hydrocarbon.
(ii) Aqueous bromine is used to show the difference between a saturated hydrocarbon and an unsaturated hydrocarbon.
Describe the result of the test with a saturated hydrocarbon.
(c) Fig. 11.1 shows the apparatus used for the catalytic cracking of a saturated hydrocarbon.
(i) State the purpose of the catalyst in the cracking of a saturated hydrocarbon.
(ii) Cracking is an endothermic reaction.
State what is meant by an endothermic reaction.
(d) The complete combustion of hydrocarbons produces the greenhouse gas carbon dioxide.
(i) Name one other greenhouse gas.
(ii) Identify the gas in the air that reacts with hydrocarbons during combustion.
(iii) Carbon dioxide is one of the gases found in clean air.
State the name of the two gases found in clean air in the greatest proportions.
▶️Answer/Explanation
Ans : 11(a)(i) carbon = 6 ;
hydrogen = 0 ;
11(a)(ii) 6 ;
11(b)(i) unsaturated has a C=C double bond ;
11(b)(ii) aqueous bromine remains orange ;
11(c)(i) speed up the reaction ;
11(c)(ii) temperature decreases / thermal energy is absorbed (from the surroundings) ;
11(d)(i) methane ;
11(d)(ii) oxygen ;
11(d)(iii) oxygen ;
nitrogen ;
Question
Fig. 5.1 shows three hydrocarbon molecules, A, B and C.
(a) (i) Complete the dot-and-cross diagram of molecule C. Show the outer shell electrons only.
(ii) Molecule C is a greenhouse gas.
State the name of one other greenhouse gas.
…………………………………………………………………………………………………………………….
(b) The reaction between molecule A and oxygen is exothermic.
Describe what is meant by an exothermic reaction.
…………………………………………………………………………………………………………………….
…………………………………………………………………………………………………………………….
(c) State and explain which molecule A, B or C represents a molecule of ethane.
molecule …………………..
explanation …………………………………………………………………………………………………..
…………………………………………………………………………………………………………………….
(d) (i) State and explain which molecule A, B or C is unsaturated.
molecule …………………..
explanation …………………………………………………………………………………………………….
……………………………………………………………………………………………………………………..
(ii) An orange solution is used to test if a hydrocarbon molecule is unsaturated or saturated.
State the name of this orange solution.
…………………………………………………………………………………………………………………….
(iii) Describe what is observed when the solution in (ii) is reacted with an unsaturated hydrocarbon molecule.
…………………………………………………………………………………………………………………….
…………………………………………………………………………………………………………………….
▶️Answer/Explanation
Ans: 5(a)(i) 1 shared pair ;
all else correct ;
5(a)(ii) water vapour ; carbon dioxide ;
5(b) (thermal) energy released ;
5(c) B – no mark and
has formula C$_{2}$H$_{6}$ ;
5(d)(i) A – no mark and
has two carbons but only four hydrogens / has general formula C$_{n}$H$_{2n}$ ;
5(d)(ii) (aqueous) bromine ;
5(d)(iii) decolourises ;
Question
(a) An isotope of magnesium has a proton number (atomic number) of 12 and a nucleon number (mass number) of 26.
Complete Table 5.1 to show the numbers of neutrons and electrons in an atom of this isotope.
(b) Fig. 5.1 shows part of the reactivity series of metals.
Magnesium reacts slowly with cold water.
Use the reactivity series to predict the result when calcium reacts with cold water.
Explain your answer.
prediction ………………………………………………………………………………………………………………….
…………………………………………………………………………………………………………………………………
explanation ……………………………………………………………………………………………………………….
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(c) Magnesium reacts with carbon dioxide. Magnesium oxide and carbon are made.
(i) Write the word equation for this reaction.
(ii) The reaction between magnesium and carbon dioxide is exothermic.
State what is meant by the term exothermic.
……………………………………………………………………………………………………………………
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(d) Platinum is a transition metal. Magnesium is not a transition metal.
State two properties of platinum that are not properties of magnesium.
1 …………………………………………………………………………………………………………………..
2 ………………………………………………………………………………………………………………….
(e) Table 5.2 shows the composition of an alloy of magnesium.
Complete the table with the % by mass of magnesium.
Calculate the mass of magnesium in 1.0kg of the alloy.
mass = ……………………………………………. kg
▶️Answer/Explanation
Ans: 5(a)
5(b) calcium reacts quickly/quicker ;
calcium is higher in reactivity series than magnesium ;
5(c)(i) magnesium + carbon dioxide → magnesium oxide + carbon ;
5(c)(ii) releases (thermal) energy ;
5(d) any two from:
forms coloured compounds ;
acts as catalyst ;
variable valency ;
5(e) 91.5 (%) ;
0.915 (kg) ;
Question
(a) The list below shows the formulae of six molecules.
CH4 Cl2 CO N2 NH3 O2
Identify which of the molecules from the list is:
(i) an ammonia molecule (Topic – C2.2)
▶️Answer/Explanation
NH3
Explanation: Ammonia is a compound with the chemical formula NH3, consisting of one nitrogen atom and three hydrogen atoms.
(ii) a molecule used in the treatment of water (Topic – C10.1)
▶️Answer/Explanation
Cl2
Explanation: Chlorine (Cl2) is commonly used in water treatment to kill bacteria and other pathogens.
(iii) a molecule formed during the incomplete combustion of carbon-containing substances (Topic – C6.2)
▶️Answer/Explanation
CO
Explanation: Carbon monoxide (CO) is formed during the incomplete combustion of carbon-containing substances when there is insufficient oxygen.
(iv) the molecule of the gas that is 78% of clean dry air (Topic – C10.2)
▶️Answer/Explanation
N2
Explanation: Nitrogen (N2) makes up approximately 78% of the Earth’s atmosphere by volume.
(v) a molecule that contains four covalent bonds. (Topic – C2.5)
▶️Answer/Explanation
CH4
Explanation: Methane (CH4) contains four covalent bonds, one between the carbon atom and each of the four hydrogen atoms.
(b) Lime (calcium oxide) is made from limestone (calcium carbonate) by thermal decomposition.
(i) State the name of the other product of this reaction. (Topic – C6.1)
▶️Answer/Explanation
Carbon dioxide
Explanation: The thermal decomposition of calcium carbonate (CaCO3) produces calcium oxide (CaO) and carbon dioxide (CO2).
(ii) Calcium carbonate is not a fertiliser but is often added to soil. Explain why calcium carbonate is often added to soil. (Topic – C10.1)
▶️Answer/Explanation
To neutralize acidic soil
Explanation: Calcium carbonate is added to soil to neutralize acidity, improving soil pH and making it more suitable for plant growth.
(iii) List the three essential elements needed in a fertiliser. (Topic – C10.1)
▶️Answer/Explanation
1. Nitrogen
2. Phosphorus
3. Potassium
Explanation: These three elements are essential for plant growth and are commonly found in fertilizers to promote healthy development.
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.