CIE iGCSE Co-Ordinated Science C6.2 Rate of reaction 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) Fig. 8.1 shows the apparatus a student uses to investigate the rate of reaction between
magnesium and dilute hydrochloric acid.
Hydrogen gas is collected in the measuring cylinder.
The other product is aqueous magnesium chloride.
(i) Construct the word equation for this reaction.
…………………………. + ………………………….→ …………………………. + ………………………….
(ii) State two changes to the reaction conditions that increase the rate of reaction.
1 ……………………………………………………………………………………………………………………….
2 ……………………………………………………………………………………………………………………….
(iii) The reaction between magnesium and dilute hydrochloric acid is exothermic.
State the meaning of exothermic.
…………………………………………………………………………………………………………………….
(iv) The student repeats the experiment using three different metals, copper, iron and calcium.
The observations are shown in Table 8.1.
Place the four metals in order of their reactivity from the most reactive to the least reactive.
(b) Table 8.2 shows information about the four metals in a magnesium alloy.
(i) Calculate the percentage of magnesium contained in the alloy.
percentage of magnesium = …………………………………………….. %
(ii) Calculate the mass of aluminium contained in 20kg of the alloy.
mass of aluminium = ……………………………………………. kg
(iii) Suggest why, apart from cost, this alloy of magnesium is used rather than pure
magnesium for making parts for car engines.
…………………………………………………………………………………………………………………….
…………………………………………………………………………………………………………………….
▶️Answer/Explanation
Ans: 8(a)(i) magnesium + hydrochloric acid → magnesium chloride + hydrogen ;
8(a)(ii) any two from:
increase temperature (of acid) ;
increase concentration (of acid) ;
decrease particle size / increase surface area of magnesium ;
8(a)(iii) releases thermal energy ;
8(a)(iv) calcium
magnesium
iron
copper ;
8(b)(i) 89 (%) ;
8(b)(ii) 1.8 (kg) ;
8(b)(iii) stronger ;
Question
(a) Limestone is insoluble in water.
Limestone is mixed with water and poured through filter paper.
(i) Explain how filter paper separates limestone from water.
(ii) The filtrate is tested to find its pH number.
One way of finding the pH number is to use a pH meter.
Describe one other way to find the pH number of the filtrate.
(b) Limestone is sometimes added to soil to reduce soil acidity.
Limestone is mainly calcium carbonate which reacts with acid.
(i) This soil treatment adds carbon dioxide to the atmosphere.
State one other reason why the amount of carbon dioxide in the atmosphere is increasing.
(ii) Describe how an increase in carbon dioxide in the atmosphere affects the environment.
(c) A student investigates the rate of reaction between excess dilute hydrochloric acid and a piece of limestone.
Fig. 11.1 shows the apparatus used.
The student measures the volume of carbon dioxide in the measuring cylinder every 20 seconds for 280 seconds.
A graph of the student’s results is shown in Fig. 11.2.
(i) Use Fig. 11.2 to find the total volume of carbon dioxide released.
volume = ………………………………………….. cm3
(ii) Use Fig. 11.2 to find the time when the reaction finished.
time = ……………………………………………… s
(iii) The student repeats the experiment at a higher temperature.
On Fig. 11.2, sketch a line to show the results.
(iv) Increasing the temperature increases the rate of reaction.
State two other ways the student can increase the rate of the reaction.
1 ……………………………………………………………………………………..
2 …………………………………………………………………………………….
▶️Answer/Explanation
Ans : 11(a)(i) limestone does not pass through (the holes in) the filter paper and water does pass through (the holes in) the filter paper ;
limestone particles are larger / water particles are smaller (than the holes in the filter paper) ;
11(a)(ii) use universal indicator (paper / solution) ;
use colour to determine pH from chart ;
11(b)(i) combustion of carbon containing fuels ;
11(b)(ii) global warming / climate change ;
11(c)(i) 45 (cm3) ;
11(c)(ii) 190 (s) ;
11(c)(iii) steeper line ;
but levelling off at 45 (cm3) ;
11(c)(iv) decrease particle size / use powder / increase surface area ;
increase acid concentration ;
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
(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.