CIE iGCSE Co-Ordinated Science C8.5 Noble gases Exam Style Questions Paper 3
Question
(a) A list of formulae is shown.
CH $_{4}$ Cl $_{2}$ MgCl $_{2}$ N$_{2}$ NaCl NH $_{3}$ O$_{2}$
Identify the formula from the list which represents:
(i) a compound that is the main constituent of natural gas
(ii) an element that bleaches damp litmus paper
(iii) an element that makes up 21% of clean air
(iv) a compound containing an ion with a 1+ charge
(v) a gas made by displacement from an ammonium salt.
(b) A student investigates the rate of reaction between excess dilute hydrochloric acid and powdered magnesium carbonate.
Carbon dioxide gas is produced in this reaction.
Fig. 2.1 shows the apparatus the student uses.
The student measures the mass of the conical flask and its contents during the reaction.
(i) Explain why the mass of the conical flask and its contents decreases during the reaction.
(ii) The student wants to increase the rate of reaction. They do not change the particle size of the magnesium carbonate.
State two changes to the reaction conditions that the student makes to increase the rate of reaction.
iii) Complete the word equation for the reaction
c) Magnesium chloride is soluble in water.
State the separation technique used to obtain solid magnesium chloride from a solution of magnesium chloride.
▶️Answer/Explanation
Ans : 2(a)(i) CH4 ;
2(a)(ii) Cl2 ;
2(a)(iii) O2 ;
2(a)(iv) NaCl ;
2(a)(v) NH3 ;
2(b)(i) carbon dioxide is lost ;
2(b)(ii) increase temperature (of acid) ;
increase concentration (of acid) ;
2(b)(iii) carbon dioxide ;
water ;
2(c) crystallisation ;
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 ;