CHEM V METALS

SODIUM METAL
The diagram below shows the extraction of sodium metal using the Downs’ cell. Study it and answer the questions that follow;
NaCl in Gas
Molten sodium

Circular steel cathode



-ve
(-

(+ve)


Steel gauze cylinder
a) Explain why in this process the sodium chloride is mixed with calcium chloride.
- To lower melting point of sodium chloride from 800oC to 600oC hence reducing the cost of production of sodium.
b) Why is the anode made of graphite and not steel?
- Steel would react with chloride while graphite will not.
c) State two properties of sodium metal that make it possible for it to be collected as shown in the diagram
- Melting point lower than that of the electrolyte.
- Less dense than the electrolyte.
d) What is the function of the steel gauze cylinder?
- To prevent the chlorine and sodium from mixing/coming into contact.
e) Write an ionic equation for the reactions, which take place at the anode and cathode.
- I Cathode: - Na+(l) +e Na (l)
- II Anode: - 2Cl-(l) Cl2 (g) + 2e-

f) Give one industrial use of sodium and explain why it is stored under kerosene.
- Sodium vapor in street lamps
- Extraction of titanium.
- Manufacture of sodium peroxide.
- Make alloy with copper or lead.
Sodium is extracted by the electrolysis of fused sodium chloride.
- To free ions for easy discharge.
a) Why will fused sodium chloride conduct electricity but not solid sodium chloride?
- Have free ions.
b) The sodium chloride is mixed with a little calcium chloride flux and is made molten. Explain why.
- Lower melting point from 800oC to 600oC.




ZINC METAL
State two ores of Zinc metal.
- Zinc blende.
- Calamine (ZnCO3)
b) An ore is suspected to contain zinc as a constituent. Explain how presence of zinc can be confirmed.
- Add dilute nitric acid to the ore
- Filter
- To one portion add sodium hydroxide till excess, white precipitate formed, soluble in excess.
- To another portion add ammonia a white precipitate soluble in excess.
c) Name three substances that are used to concentrate an ore of zinc by froth-floatation.
- Oil
- Water
- Air
d) During the process of extraction of zinc metal the ores are first roasted in air to form metal oxides. Explain why this is important.
- The oxides are easier to reduce.
e) Zinc oxide is reduced by coke as shown by the equation below to form zinc metal and carbon monoxide.
ZnO(s) + C(s) Zn(s) + CO (g)
If 243 Kg of zinc oxide and 24Kg of coke were used, calculate the
Mass of zinc metal formed. [C=12, O=16 Zn= 65]
Mole of C = 24000/12 = 2000moles
Mole ratio Zn: C = 1:1 there for ZnO is in excess
Mass of Zn = 2000 x 65 = 130000g or 130 Kg
f) Study the set up below and answer the questions that follow.
Zinc
Gas X


Water
Heat

i) Explain the observations made the combustion tube.
- A white residue is formed
j) Write a balanced equation for the reaction in combustion tube.
- Zn(s) + H2O (g) ZnO(s) +H2 (g)
k) How would you test for gas X
- Introduce a burning splint in the gas jar full of X. It burns with a pop sound
l) State four uses of gas X in industries
- Manufacture of hydrochloric acid.
- Wielding, oxy-hydrogen flame (200oC) used in wielding.
- Manufacture of ammonia.
- Hardening of oils.
m) Identify two pollutants gases produced during the extraction of zinc metal.
- Carbon monoxide.
- Sulpur dioxide.
n) Explain how zinc is used in preventing rusting.
- By coating/galvanizing iron.


Study the flow chart below and answer the questions that follow.
Gas gas
ZnS O2 ZnO(s) Coke Zn(s)
Heat step 1 Step 2 Step 3


ZnSO4 (aq) + Water Gas D

a) State the conditions necessary for the reaction in step 2.
- Heat.
- High temperature.
b) Name gas D and three uses of Zinc.
- Sulphur dioxide
1. In batteries.
2. Galvanizing of iron Electroplating.

IRON METAL
An iron ore suspected to contain mainly iron. Describe a method that can be used to confirm the presence of iron in the ore.
- To the sample add sulphuric acid or hydrochloric acid and warm
- Filter the mixture
- To a portion of the filtrate add sodium hydroxide or ammonium hydroxide drop wise until in excess.
- Formation of dirty green precipate shows presence of iron II ions
Iron is extracted from its ore by the blast furnace process.
a) Name three ores from which iron is extracted.
- Haematite.
- Siderite.
- Magnetite.
a) One of the impurities in iron ore is removed in the form of calcium silicate. Write an equation for the reaction in which calcium silicate is produced.
CaO(s) + SiO2 (g) CaSiO3(l)

IRON ORE

Process R

SUBSTANCE A IRON (III) CHLORIDE SUBSTANCE B


BLAST FURNACE


The scheme above shows part of the extraction of iron from its ores. Study
It and answer the questions that follow
i) Name process R.
- Roasting or burning in air.
ii) Substances A and B are added to iron (iii) oxide below they are dropped into the blast furnace name A and B.
A = Coke
B = Limestone
iii) Briefly explain the functions of A and B.
- A Burns to form carbon (IV) oxide, which is reduced to carbon monoxide, which reduces the iron oxide to the metal.
- When heated decomposes to calcium oxide and carbon monoxide. The carbon dioxide is recycled and calcium oxide combines with acidic oxide to form slag.
iv) Iron obtained from the blast furnace is 90-95% pure. List two impurities present in raw iron.
- Carbon.
- Silicon.
- Manganese.
- Sulpur.
- Phosphorus.

Study the flow chart below and answer the questions that follow.
Light green Brown solid + Gas N + Gas P + 7moles of water
Solid K M
Dil. H2SO4

Fe (SO4) 3
b) Name substances; M, K, N, P.
- M; Iron (III) oxide.
- Iron (II) suphate.
- Sulphur trioxide.
- Sulphur dioxide.
c) Write a balanced equation for the reaction that took place when solid K was heated.
2FeSO4.7H2O(s) Fe2O3 +SO3+SO2+4H2O

Iron ore, coke, limestone and air are used in the blast furnace in the manufacture of iron. The reducing agent in the process is carbon monoxide.
a) Explain how the carbon monoxide is formed in the furnace.
C +O2 CO2
CO2 + C CO
b) Give the equation for the reaction in which iron is formed.
Fe2O3(s) +3CO (g) 2Fe (l) +3CO2 (g)
c) What is the importance of the limestone?
- Remove impurities.
- Generate carbon dioxide.
Give the role of slag formed during the manufacture of iron.
- Prevent re oxidation of iron.
List three uses of slag.
- Make fertilizers.
- Make cement.
- Building materials.








ALUMINIUM METAL
Study the flow chart below and answer the questions that follow.

Bauxite (Al2O3) with iron oxides
and silicates as impurities.

T


Solutions containing (Al (OH)-4 ions Residue

Precipitation and heating

Solid aluminium Oxide

Heat

Molten Aluminium oxide Electrolysis Molten Aluminium




Duralium alloy for aircraft parts frames Metal foil lining for food packets

i) Suggest a purpose for the industrial process represented by the flow chart.
- Extraction of aluminium, processing/refining of
ii) Explain how process T is carried out (equations not necessary)
- Bauxite is dissolved in sodium hydroxide, iron impurities ppt as iron (iii) hydroxide, then filtered off Carbon (IV) oxide is bubbled through aluminium hydroxide to ppt it.
iii) Explain why it is necessary to heat aluminium oxide before electrolysis is carried out.
- Make it molten (molten ore)
- Free the ions, Al3+ O2-
iv) What properties of aluminium and its alloy make them suitable for uses indicated? (At least five).
- Low density/light.
- Low tensile strength (can be stretched).
- Good conductor of heat.
- Not easily corroded by cooking because of un reactive coating of aluminium oxide.
- Reducing agent in thermite process.
The extraction of aluminium from its ore is two stages, purification stage and electrolysis stage. The melting point of aluminium oxide is 2054oC but electrolysis is carried out between 800-900oC.
a) Why is electrolysis not carried out at 2054oC?
- High temperature would facilitate the ignition or sparking of carbon electrodes. The carbon electrodes could burn at high temperatures. The fuel required to maintain high temperature is a lot hence expensive. The high temperatures could exceed the sublimation point of graphite.
b) What is done to lower the temperature?
- Adding cryolite or Na3AlF6





Aluminium chloride dissolves in water to form an acidic solution. Using equations explain how the acidic solution is formed.
- Aluminium chloride dissolves in water to form hydrated aluminium.
- AlCl3 +6H2O [Al (H2O) 6] 2+ +3Cl-
- The hydrated ion is hydrolyzed
- [Al (H2O) 6] 3+ +H2O [Al (H2O) 5 OH] 2+ + H3O+
The extraction of aluminium from its ores takes place in two stages, purification stage and electrolysis stage. The diagram below shows the set up for the electrolysis stage.
Anode




Electrolyte





i) Name the ore from which aluminium is extracted.
- Bauxite.
ii) Name one impurity, which is removed at the purification stage.
- Iron (II) oxide/Silicon (IV) oxide? Silica.
iii) Label the diagram each of the following
I) Anode.
II) Cathode.
III) Region containing electrolyte.
iv) The aluminium, which is produced, is tapped off as a liquid. What does this suggest about its melting point.
- The melting point is below 800oC.
The basic raw materials for extraction of aluminium are bauxite.
a) Name the method that is used to extract aluminium from bauxite.
- Electrolysis/hall/Heroult cell.
b) Write the chemical formulae of the major component of bauxite.
- Al2O3/Al2O3.H2O/Al2O3.2H2O.
c) Name the major impurities in bauxite.
- Iron (III) oxide, Fe2O3
- Silica, SiO2.
d) Explain how the impurities in bauxite are removed.
- Add hot concentrated sodium hydroxide/ potassium hydroxide, silica and aluminium oxide dissolve, filter iron (II) oxide.
- Bubble carbon (iv) oxide; add water and aluminium hydroxide to the filtrate to ppt aluminium hydroxide filter the aluminium hydroxide silicates remain in solution.