Edexcel IGCSE Chemistry Chapter 7, page 59 ANSWERS
1 a) Refer to Fig 7.5 p 55. Note that gas-collecting apparatus is essentially the same whether
collecting O2 or CO2 (Fig 7.12, p 58)
b) 2H2O2 (aq)
2H2O(l) + O2(g)
c) Introduce a glowing splint into the container with the gas. If it relights, it is oxygen.
2 a) sulfur [S + O2
SO2 and SO2 + H2O
H2SO3 (sulfurous acid)]
b) sodium (recall it is in Group 1, which all share these properties; hence the term ‘alkali metals’
for the group).
c) copper (recall CuO is a black powder)
d) carbon will burn in oxygen to give carbon dioxide gas which turns limewater milky. Describing
it a ‘shiny grey’ is possibly misleading. Although graphite is shiny, it is very dark grey (i.e. pencil
lead).
3 a) burn a metal such as copper, that will yield a solid product.
2Cu(s) + O2(g)
2CuO(s)
b) dissolve it in water
c) 3Mg(s) +
N2(g)
Mg3N2(s)
d) Argon is more dense than nitrogen. Pure nitrogen has a lower density than nitrogen mixed
with even a tiny quantity of argon.
e) krypton and xenon (also neon, helium)
4 a) Carbon dioxide will not support combustion, so works by smothering the flames.
b) Carbon dioxide is in solution in fizzy drinks. The amount able to be dissolved depends on the
pressure of the system. A bottle with the lid on is under higher pressure than an open bottle.
Removing the lid suddenly lowers the pressure, so CO2(aq) becomes CO2(g) and bubbles appear.
c) Sulfur burns to produce sulfur dioxide, which will dissolve in water in the atmosphere and
form sulfurous or sulfuric acids. When this water falls as rain, it will be acidic.
d) The sparks used to ignite petrol inside a car engine also break the triple bonds in N2
molecules. The nitrogen atoms then react with O2 in the air to produce oxides of nitrogen.
e) The catalyst must heat up to work efficiently. Using a car for a short journey will not allow the
catalyst to heat up enough, so the catalytic converter will not work properly.