CIE iGCSE Co-Ordinated Science C10.1 Water 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) Ice is a solid. Water is a liquid. Steam is a gas.
Fig. 5.1 shows the different arrangement of the particles in ice, water and steam.
State and explain which diagram, A, B or C, shows the arrangement of particles in ice, water or steam.
ice is diagram ………….
explanation ……………………………………………………………………………………………………………….
…………………………………………………………………………………………………………………………………
water is diagram ………….
explanation ……………………………………………………………………………………………………………….
…………………………………………………………………………………………………………………………………
steam is diagram ………….
explanation ……………………………………………………………………………………………………………….
…………………………………………………………………………………………………………………………………
(b) A few drops of water are left in a cup in a warm room.
After a few hours, no water is left in the cup.
State the name of the process that has occurred.
……………………………………………………………………………………………………………………………
(c) Water is neutral.
State the pH number of pure water.
pH = ……………………..
(d) State why chlorine is added to water to make it safe to drink.
…………………………………………………………………………………………………………………………………
…………………………………………………………………………………………………………………………………
(e) The electronic structures for oxygen and hydrogen are shown in Fig. 5.2.
Complete the dot‐and‐cross diagram in Fig. 5.3 to show the arrangement of electrons in a molecule of water.
Show the outer‐shell electrons only.
(f) Sodium chloride is a solute. Water is a solvent.
Define the terms solute and solvent.
solute ……………………………………………………………………………………………………………………….
…………………………………………………………………………………………………………………………………
solvent ……………………………………………………………………………………………………………………..
…………………………………………………………………………………………………………………………………
▶️Answer/Explanation
Ans : 5(a) ice is C – particles are in regular arrangement
water is B – particles are (mostly) touching and irregular arrangement
steam is A – particles are widely spaced
C B A ;
one correct explanation ;
three correct explanations ;
5(b) evaporation ;
5(c) 7 ;
5(d) kills bacteria ;
5(e)
1 pair of bonding electrons ;
all else correct ;
5(f) a solute – a substance that is dissolved in a solvent ;
a solvent – a substance / liquid that dissolves a solute ;
Question
(a) (i) Fig. 8.1 shows the changes of state of water
Identify the changes of state represented by X and Y.
X ……………………………………………………………………………………………………………………….
Y ……………………………………………………………………………………………………………………….
(ii) State if boiling is a chemical change or a physical change.
Give a reason for your answer.
change ………………………………………………………………………………………………………………
reason ……………………………………………………………………………………………………………….
………………………………………………………………………………………………………………………….
(b) (i) Complete the dot-and-cross diagram to show the electron arrangement in a molecule of water.
Show outer shell electrons only.
(ii) State the type of chemical bonds in a water molecule.
…………………………………………………………………………………………………………………….
(c) Filtration and chlorination are both used in the treatment of the water supply.
State the purpose of each process.
filtration …………………………………………………………………………………………………………………….
…………………………………………………………………………………………………………………………………
chlorination ……………………………………………………………………………………………………………….
…………………………………………………………………………………………………………………………………
(d) Water is made when hydrogen reacts with oxygen.
Balance the symbol equation for the reaction between hydrogen and oxygen.
………….. H$_{2}$ + O$_{2}$ → ………….. H$_{2}$O
▶️Answer/Explanation
Ans : 8(a)(i) X = condensation ;
Y = solidification or freezing ;
8(a)(ii) physical (no mark) ;
no new substance formed / can be reversed ;
8(b)(i)
one pair of bonding electrons ;
all else correct ;
8(b)(ii) covalent ;
8(c) filtration – remove solid matter OWTTE ;
chlorination – kill bacteria / microorganisms ;
8(d) 2 H$_{2}$ + O$_{2}$ → 2 H$_{2}$O
2H$_{2}$ ;
2H$_{2}$O ;
Question
(a) Fig. 4.1 shows some different sources of pollution of the water in seas.
(i) Complete the sentences using information from Fig. 4.1.
The two biggest sources of pollution are ………………………………………… and ………………………………………… .
The total percentage of pollution caused by chemical waste is ………………………………………… %.
The percentage of pollution caused by discarded rubbish is ………………………………………… %.
(ii) Suggest one negative impact of untreated sewage on humans.
(b) Polluted water affects the growth of plants.
A scientist measures the height of two pea plants, A and B, for one month.
Plant A is given unpolluted water.
Plant B is given polluted water.
Table 4.1 shows the increase in height for each plant.
(i) Calculate the difference in increase in height between plant A and plant B from Table 4.1.
…………………………………………………………………………………………….. cm [1]
(ii) Water is needed for germination of seeds.
State two other environmental conditions required for germination.
1 ……………………………………………………………………………
2 …………………………………………………………………………..
▶️Answer/Explanation
Ans : 4(a)(i) agriculture and (untreated) sewage ;
41 (%) ;
5 (%) ;
4(a)(ii) any one from:
spread diseases ;
AVP ;
4(b)(i) (29 – 11) = 18 (cm) ;
4(b)(ii) warm / suitable temperature ;
oxygen ;
Question
A sample of clean air is a mixture of oxygen, nitrogen and small quantities of noble gases, water vapour and carbon dioxide.
(a) State the percentage of oxygen gas and nitrogen gas in clean air.
oxygen = ………………………………………………….. %
nitrogen = ………………………………………………….. %
(b) State the name of a noble gas and give a use for this noble gas.
name …………………………………………………………………………
use …………………………………………………………………………
(c) Water is made when hydrogen gas reacts with oxygen gas.
Look at the symbol equation for the reaction between hydrogen and oxygen.
This equation is not balanced.
H2 + O2 → H2O
(i) Explain why this equation is not balanced.
(ii) Another way that water is made is by the decomposition of hydrogen peroxide, H2O2.
Oxygen is also made.
Balance the symbol equation for this reaction.
…………H2O2 → …………H2O + O2
(iii) Complete the dot-and-cross diagram in Fig. 5.1 to show the bonding in a molecule of water, H2O.
Show only the outer-shell electrons.
(iv) Name the type of chemical bonding in a molecule of water.
(v) Describe a chemical test for water and give the positive result.
test ………………………………………………………………………………
positive result ……………………………………………………………..
▶️Answer/Explanation
Ans : 5(a) oxygen – 21% ;
nitrogen – 78% ;
5(b) named noble gas ;
correct use ;
5(c)(i) nos of oxygen atoms is different on LHS to RHS ;
5(c)(ii) 2 H2O2 → 2 H2O × O2 ;
5(c)(iii) 
1 shared pair ;
all else correct ;
5(c)(iv) covalent (bonds) ;
5(c)(v) anhydrous copper sulfate ;
white to blue ;
OR
cobalt chloride (paper) ;
blue to pink ;
Question
(a) The list below shows some chemical processes.
chlorination chromatography cracking
crystallisation decomposition
electrolysis fractional distillation polymerisation
Identify the process from the list that is used:
(i) in the treatment of drinking water
…………………………………………………………………………………………………………………….
(ii) to separate a mixture of dyes
…………………………………………………………………………………………………………………….
(iii) to extract aluminium from bauxite
…………………………………………………………………………………………………………………….
(iv) to produce long chain molecules from monomer units.
…………………………………………………………………………………………………………………….
(b) When dilute hydrochloric acid is added to aqueous sodium hydroxide, a neutralisation reaction occurs.
Fig. 2.1 shows apparatus used to investigate the change in pH as the acid is added.
(i) State the name of apparatus A.
…………………………………………………………………………………………………………………….
(ii) State the reading on the pH meter when the dilute hydrochloric acid exactly neutralises
the aqueous sodium hydroxide.
…………………………………………………………………………………………………………………….
(iii) State the two products of the reaction shown in Fig. 2.1.
1 ……………………………………………………………………………………………………………………….
2 ……………………………………………………………………………………………………………………….
(c) Describe what is observed when aqueous sodium hydroxide is added to blue copper(II) sulfate solution.
…………………………………………………………………………………………………………………………….
……………………………………………………………………………………………………………………………
▶️Answer/Explanation
Ans: 2(a)(i) chlorination ;
2(a)(ii) chromatography ;
2(a)(iii) electrolysis ;
2(a)(iv) polymerisation ;
2(b)(i) burette ;
2(b)(ii) 7 ;
2(b)(iii) sodium chloride ;
water ;
2(c) pale blue precipitate ;
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
(a) Orange bromine gas, Br$_{2}$, is put into the bottom of a gas jar which is immediately sealed.
After a short time, the bromine gas spreads out to fill the gas jar.
This process is called diffusion.
Fig. 11.1 shows the diffusion of bromine.
Describe the process of diffusion in terms of the movement of particles.
…………………………………………………………………………………………………………………………………
…………………………………………………………………………………………………………………………………
…………………………………………………………………………………………………………………………………
(b) Chlorine and bromine are both halogens.
State the name of one other element that is a halogen.
…………………………………………………………………………………………………………………………………
(c) Chlorine is in Period 3 of the Periodic Table.
Describe the change in metallic character across Period 3.
…………………………………………………………………………………………………………………………………
…………………………………………………………………………………………………………………………………
(d) Explain why the drinking water for a city is treated with chlorine.
…………………………………………………………………………………………………………………………………
……………………………………………………………………………………………………………………………
(e) Complete the dot-and-cross diagram to show the bonding in a molecule of chlorine Cl$_{2}$.
Only show the outer shell electrons.
(f) Hydrogen and chlorine combine to make hydrogen chloride, HCl.
(i) Balance the symbol equation for this reaction.
H$_{2}$ + Cl$_{2}$→ …….. HCl
(ii) Explain why hydrogen chloride is a covalent compound and not an ionic compound.
………………………………………………………………………………………………………………………….
…………………………………………………………………………………………………………………….
▶️Answer/Explanation
Ans: 11(a) gas particles in (constant) random motion ;
(particles move) from region of high concentration to region of low concentration ;
11(b) iodine / fluorine / astatine ;
11(c) metallic to non-metallic (from left to right) ;
11(d) to kill, microorganisms/bacteria/pathogens ;
11(e) shared pair ;
correct number of electrons on each atom / 14 electrons in total ;
11(f)(i) 2 HCl ;
11(f)(ii) two non-metals bonding / shared pair of electrons ;