Question
Lead is an excellent roofing material. It is malleable and resistant to corrosion. Lead rapidly becomes coated with basic lead carbonate which protects it from further corrosion.
(a) Lead has a typical metallic structure which is a lattice of lead ions surrounded by a ‘sea’ of mobile electrons. This structure is held together by attractive forces called a metallic bond.
(i) Explain why there are attractive forces in a metallic structure.[2]
(ii) Explain why a metal, such as lead, is malleable.[2]
(b) Basic lead(II) carbonate is heated in the apparatus shown below. Water and carbon dioxide are produced.
(i) Silica gel absorbs water. Silica gel often contains anhydrous cobalt(II) chloride. When this absorbs water it changes from blue to pink.
Suggest a reason.[1]
(ii) Soda lime is a mixture of sodium hydroxide and calcium oxide. Why do these two substances react with carbon dioxide?[2]
(iii) Name two substances formed when soda lime reacts with carbon dioxide.[2]
(c) Basic lead(II) carbonate has a formula of the type xPbCO3.yPb(OH)2 where x and y are whole numbers.
Determine x and y from the following information.
PbCO3 → PbO + CO2
Pb(OH)2 → PbO + H2O
When heated, the basic lead(II) carbonate gave 2.112 g of carbon dioxide and 0.432 g of water.
Mass of one mole of CO2 = 44g
Mass of one mole of H2O = 18g
Number of moles of CO2 formed = [1]
Number of moles of H2O formed = [1]
x = ___ and y = ___
Formula of basic lead(II) carbonate is ___ [1] [Total: 12]
Answer/Explanation
Ans:
(a) (i) (attractive force between) positive ions
and (negative) electrons
opposite charges attract ONLY [1]
electrostatic attraction ONLY [1]
(ii) lattice / rows / layers of lead ions / cations / positive ions
NOT: atoms / protons / nuclei
can slide past each other / the bonds are non-directional
(b) (i) anhydrous cobalt chloride becomes hydrated
ACCEPT: hydrous
(ii) carbon dioxide is acidic
sodium hydroxide and calcium oxide are bases / alkalis
(iii) Any two of:
water, calcium carbonate and sodium carbonate
ACCEPT: sodium bicarbonate
(c) number of moles of CO2 formed = 2.112 / 44 = 0.048
number of moles of H2O formed = 0.432 / 18 = 0.024
x = 2 and y = 1 NOT: ecf from this line
formula is 2PbCO3.Pb(OH)2 / Pb(OH)2. 2PbCO3
Question
There are three types of giant structure – ionic, metallic and giant covalent.
(a) In an ionic compound, the ions are held in a lattice by strong forces.
(i) Explain the term lattice.[2]
(ii) Explain how the ions are held together by strong forces.[1]
(b) Describe the bonding in a typical metal.[3]
(c) The electrical conductivities of the three types of giant structure are given in the following table.
Explain the differences in electrical conductivity between the three types of giant structure and the difference, if any, between the solid and liquid states of the same structure.[5] [Total: 11]
Answer/Explanation
Ans:
(a) (i) regular arrangement / repeating pattern NOT structure
cond: ions
not molecules / atoms
(ii) attraction between opposite charges / electrostatic attraction
(b) delocalized / mobile / free / sea of electrons
positive ions / cations
not atoms / protons / nuclei
attraction between these electrons and ions
(c) giant covalent
no ions
no delocalized / free / mobile / sea of electrons or all electrons
ionic
in ionic solid ions cannot move
liquid ionic compound ions can move
metallic
(both solid and liquid) metals have delocalized (or alternative term) electrons