NECTA CHEMISTRY 2015 -ANSWERS
CHEMISTRY 2015
1.
i ii iii iv v vi vii viii ix x
B C C B D D C B B B
2.
i ii iii iv v vi vii viii ix x
O C D A I E H F I J
3. (a) (i) Two conditions that are necessary for iron to rust are water (or moisture) and
oxygen.
oxygen.
(ii) The following are some of the methods used to prevent iron from rusting:
Painting Painting the iron article creates a waterproof and airproof cover over
the surface of the iron. This method is widespread for objects ranging in size from
ships and bridges to garden gates. Paints that contain lead or zinc are mostly used.
These paints are especially good for preventing rusting. For example, "red lead" paints
contain an oxide of lead, Pb3O4. As oxygen and water cannot reach the iron,
it does not rust. However, if the paint layer is scratched off rusting may occur.
So, regular repainting is necessary to keep this protection intact.
the surface of the iron. This method is widespread for objects ranging in size from
ships and bridges to garden gates. Paints that contain lead or zinc are mostly used.
These paints are especially good for preventing rusting. For example, "red lead" paints
contain an oxide of lead, Pb3O4. As oxygen and water cannot reach the iron,
it does not rust. However, if the paint layer is scratched off rusting may occur.
So, regular repainting is necessary to keep this protection intact.
Oiling and greasing The oiling and/or greasing of the moving parts of machinery
forms a protective film, preventing rusting. Moving parts cannot be painted since the
paint layer can be easily scratched off during movement. Again, the treatment must be
repeated to continue the protection.
forms a protective film, preventing rusting. Moving parts cannot be painted since the
paint layer can be easily scratched off during movement. Again, the treatment must be
repeated to continue the protection.
Plastic coating Steel is coated with plastic for use in garden chairs, refrigerators,
bicycle baskets, dish racks, etc. The plastic PVC (polyvinyl chloride), a trade name
for polychloroethene, is often used for this purpose. Plastic is cheap and can be made
to look attractive.
bicycle baskets, dish racks, etc. The plastic PVC (polyvinyl chloride), a trade name
for polychloroethene, is often used for this purpose. Plastic is cheap and can be made
to look attractive.
Electroplating Electroplating is the coating of one metal with a layer of another metal
by means of electrolysis, where the metal to be coated is the cathode and the coating
metal the anode.
by means of electrolysis, where the metal to be coated is the cathode and the coating
metal the anode.
An iron or steel object can be electroplated with a layer of chromium or tin to protect
against rusting. A ‘tin can’ is made of steel coated on both sides with a fine layer of tin.
Tin is used because it is unreactive and non-toxic. However, if protective layer is
against rusting. A ‘tin can’ is made of steel coated on both sides with a fine layer of tin.
Tin is used because it is unreactive and non-toxic. However, if protective layer is
broken, then the steel beneath will begin to rust. So, proper handling of tin-plated
items is needed.
items is needed.
Galvanizing An iron object may be covered with a layer of zinc. This is called
galvanizing. Even if the zinc is scratched to expose the iron, the iron does not rust.
This is because zinc is higher in the reactivity series than iron. So, zinc reacts with
water and oxygen in preference to iron.
galvanizing. Even if the zinc is scratched to expose the iron, the iron does not rust.
This is because zinc is higher in the reactivity series than iron. So, zinc reacts with
water and oxygen in preference to iron.
The zinc layer can be applied by several different methods. These include electroplating
or dipping the object into molten zinc. When an iron or steel article is dipped into
molten zinc and then removed, it becomes coated with a thin layer of zinc.
The zinc forms a protective coat over the surface of iron.
This process is used for dustbins, car bodies, barbed wires and motorway crash barriers.
or dipping the object into molten zinc. When an iron or steel article is dipped into
molten zinc and then removed, it becomes coated with a thin layer of zinc.
The zinc forms a protective coat over the surface of iron.
This process is used for dustbins, car bodies, barbed wires and motorway crash barriers.
Sacrificial protection This is a method of rust protection in which blocks of a metal
more reactive than iron are attached to the iron surface. Zinc and magnesium
are more reactive than iron. When blocks of zinc or magnesium are attached
to the hull of a steel ship or oil rig, it corrodes in preference to iron.
This is called sacrificial protection because the zinc or magnesium is sacrificed to protect
the iron. When the blocks are nearly eaten away, they can be replaced by fresh blocks.
Underground gas and water pipes are connected by wire to blocks of magnesium
to obtain the same protection.
more reactive than iron are attached to the iron surface. Zinc and magnesium
are more reactive than iron. When blocks of zinc or magnesium are attached
to the hull of a steel ship or oil rig, it corrodes in preference to iron.
This is called sacrificial protection because the zinc or magnesium is sacrificed to protect
the iron. When the blocks are nearly eaten away, they can be replaced by fresh blocks.
Underground gas and water pipes are connected by wire to blocks of magnesium
to obtain the same protection.
It is not necessary to cover the whole surface of a steel article with the more reactive
metal for sacrificial protection to work. A ship may have magnesium blocks riveted to
its hull every few metres to prevent rusting of the whole hull.
metal for sacrificial protection to work. A ship may have magnesium blocks riveted to
its hull every few metres to prevent rusting of the whole hull.
Alloying Alloys are mixtures of metals. For example, iron can be mixed with small
quantities of much less reactive metals to form an alloy called stainless steel.
Stainless steel contains iron mixed with chromium, nickel and manganese.
Stainless steel does not rust. It also has a very attractive appearance. It is used to
make cutlery and kitchen equipment.
quantities of much less reactive metals to form an alloy called stainless steel.
Stainless steel contains iron mixed with chromium, nickel and manganese.
Stainless steel does not rust. It also has a very attractive appearance. It is used to
make cutlery and kitchen equipment.
Use of silica gel Silica is a common name for silicon dioxide (SiO2). Silica gel
is a granular, vitreous, highly porous form of silica made synthetically from
sodium silicate. Despite its name, silica gel is a solid. It is used as a desiccant,
which absorbs moisture to prevent rusting of iron items or articles. Most often,
a small bag of silica gel is put inside bags or boxes used for storing or
carrying iron items to absorb any moisture that may cause rusting.
is a granular, vitreous, highly porous form of silica made synthetically from
sodium silicate. Despite its name, silica gel is a solid. It is used as a desiccant,
which absorbs moisture to prevent rusting of iron items or articles. Most often,
a small bag of silica gel is put inside bags or boxes used for storing or
carrying iron items to absorb any moisture that may cause rusting.
(b) Aluminium is used in overhead cables because of possessing the following
properties:
properties:
- Aluminium is a good conduction of electricity.
- It has a low density and hence weight. Low density gives it an advantage over
copper. - It resists corrosion, in that it does not rust easily. When aluminium comes
in contact with oxygen, it reacts to form a very thin layer of its oxide on the surface,
which stops air and water getting to the metal, a condition which
makes it resist corrosion.
in contact with oxygen, it reacts to form a very thin layer of its oxide on the surface,
which stops air and water getting to the metal, a condition which
makes it resist corrosion.
4. (a) Examples of gaseous and solid fuels are as indicated hereunder:
(i) Solid fuels – firewood, coke, coal, and charcoal.
(ii) Gaseous fuel – biogas, water gas, producer gas, and natural gas.
(b) (i) Consider the following equilibrium reaction equation:
CO(g) + 2H2(g) ⇌ CH3OH (g) ; ΔH = -94kJmol-1
Explained below are the reasons why an increase in pressure gives a better yield of
methanol:
methanol:
- If pressure increases on a gaseous system, the gases are compressed.
The total number of molecules per unit volume increases. This means that the
molar concentrations of gases increase. Therefore, applying the pressure on the
above equation will favour the forward reaction and hence lead to an increase in
the amount of methanol.
The total number of molecules per unit volume increases. This means that the
molar concentrations of gases increase. Therefore, applying the pressure on the
above equation will favour the forward reaction and hence lead to an increase in
the amount of methanol.
- In the above equation, there are 3 moles of the reactants (I mole of CO and 2 moles
of 2H2) while there is only one mole of the methanol (CH3OH). If the number of moles
of the reactant(s) is higher than that of the product(s), increase in pressure will favour t
he forward reaction and vice versa. Hence, increase in pressure will lead to increased
production (yield) of methanol.
of 2H2) while there is only one mole of the methanol (CH3OH). If the number of moles
of the reactant(s) is higher than that of the product(s), increase in pressure will favour t
he forward reaction and vice versa. Hence, increase in pressure will lead to increased
production (yield) of methanol.
(ii) Because ΔH is negative, it tells us that this is an exothermic reaction.
(iii) Since the reaction is exothermic, a low temperature will increase the rate
of a forward reaction and hence the yield of methanol. This is in accordance to
Vant Hoff’s Law of Mobile Equilibrium, which states that “if a system is in equilibrium,
raising the temperature will favour the reaction which is accompanied by absorption
of heat, and lowering the temperature will favour that reaction which is accompanied
by the evolution of heat.”
of a forward reaction and hence the yield of methanol. This is in accordance to
Vant Hoff’s Law of Mobile Equilibrium, which states that “if a system is in equilibrium,
raising the temperature will favour the reaction which is accompanied by absorption
of heat, and lowering the temperature will favour that reaction which is accompanied
by the evolution of heat.”
5. (a) (i) The Group 1 elements have similar properties because of the electronic
structure of their atoms - they all have one electron in their outer shell. In chemical
reactions, all atoms in Group 1 lose one electron from their outermost shells.
structure of their atoms - they all have one electron in their outer shell. In chemical
reactions, all atoms in Group 1 lose one electron from their outermost shells.
(ii) The reactivity of group 1 elements increases down the group because, as you
go down the group:
go down the group:
- the atoms get larger;
- the outer electron gets further from the nucleus; and - the attraction between
the nucleus and outer electron gets weaker, so the electron
the nucleus and outer electron gets weaker, so the electron
is more easily lost.
(b) S/N Name of element Atomic number Electronic configuration (i) Lithium 3 2:1
(ii) Aluminium 13 2:8:3 (iii) Chlorine 17 2:8:7
(ii) Aluminium 13 2:8:3 (iii) Chlorine 17 2:8:7
6. (a) (i) Parsley (ii) Bean (iii) Tomato
(b) (i) Evaporation (ii) Sublimation (iii) Use of a magnet (magnetic separation)
7. (a) (i) Concentrated sulphuric acid, when exposed to open air, absorbs water
vapour from the air diluting itself, usually up to about three times of its original volume.
vapour from the air diluting itself, usually up to about three times of its original volume.
(ii) Upon exposure to air, iron (II) sulphate oxidizes to form a corrosive brown-yellow
coating of basic ferric sulphate, which is a mixture of ferric sulphate and ferric oxide:
coating of basic ferric sulphate, which is a mixture of ferric sulphate and ferric oxide:
12FeSO4(s) + 3O2(g) → 4Fe2(SO4)3(s) + 2Fe2O3(s)
(iii) When a bottle containing AgNO3 is left open, light will enter the bottle and the
silver nitrate (liquid) will precipitate upon exposure to light. Silver nitrate solution is
kept in brown bottles in laboratory because brown bottles stop the passage of light
through it.
silver nitrate (liquid) will precipitate upon exposure to light. Silver nitrate solution is
kept in brown bottles in laboratory because brown bottles stop the passage of light
through it.
(b) Acid-base neutralization has many applications in everyday life. The following are
some of these applications:
1. Indigestion and pain relief The dilute hydrochloric acid produced in your stomach is some of these applications:
used for digestion and killing bacteria that might have been
swallowed together with food or taken with water. However, excess acid causes
indigestion, which can be painful. To ease the pain, we take an anti-acid treatment.
Anti-acids are a broad group of compounds with no toxic effects on the body.
They are used to neutralize the effects of acid indigestion.
indigestion, which can be painful. To ease the pain, we take an anti-acid treatment.
Anti-acids are a broad group of compounds with no toxic effects on the body.
They are used to neutralize the effects of acid indigestion.
Some of these anti-acids such as milk of magnesia [insoluble magnesium hydroxide,
Mg(OH)2] help to neutralize and hence counteract the excess acid in the stomach.
This treatment, therefore, prevents indigestion and pains. The neutralization
reaction equation is:
Mg(OH)2] help to neutralize and hence counteract the excess acid in the stomach.
This treatment, therefore, prevents indigestion and pains. The neutralization
reaction equation is:
Mg(OH)2(aq) + 2HCl(aq)→ MgCl2(aq) + 2H2O(l)
Other anti-acids such as “Alka-Seltzer” contain soluble materials, including
sodium hydrogencarbonate. These tablets also contain some citric acid (a solid acid).
On adding water, the acid and some of the sodium hydrogencarbonate react, producing
carbon dioxide gas. This helps to spread and dissolve the other less soluble material.
When taken, more sodium hydrogencarbonate neutralizes the excess hydrochloric acid
in the stomach, thus easing digestion.
sodium hydrogencarbonate. These tablets also contain some citric acid (a solid acid).
On adding water, the acid and some of the sodium hydrogencarbonate react, producing
carbon dioxide gas. This helps to spread and dissolve the other less soluble material.
When taken, more sodium hydrogencarbonate neutralizes the excess hydrochloric acid
in the stomach, thus easing digestion.
Some anti-acid tablets also contain painkiller to relieve pain. “Soluble aspirin” tablets
dissolve and work in a similar way to “Alker-Seltzer” tablets. Vitamin C (ascorbic acid)
can be added to the tablets. Note that it is important to add water to start the action of
the acid.
dissolve and work in a similar way to “Alker-Seltzer” tablets. Vitamin C (ascorbic acid)
can be added to the tablets. Note that it is important to add water to start the action of
the acid.
2. Descaling kettles The limescale (CaCO3) is formed inside boilers, kettles and water
heaters when hard water is boiled. The limescale can be removed by treatment with an
acid that is strong to react with CaCO3, but not strong enough to damage the metal.
Vinegar can be used to discale kettles. Commercial “discalers” use other acid solutions
such as methanoic acid.
heaters when hard water is boiled. The limescale can be removed by treatment with an
acid that is strong to react with CaCO3, but not strong enough to damage the metal.
Vinegar can be used to discale kettles. Commercial “discalers” use other acid solutions
such as methanoic acid.
3. Prevention of tooth decay Food remnants sticking onto teeth (plaque), after eating
especially sugary food is acted upon by bacteria in your mouth. The pH of a sugar solution is 7. However, bacteria in your mouth break down the sugar in plaque to form acids, for example lactic acid. These acids lower the pH. Tooth decay begins when the pH falls below 5.8. The acid attacks the tooth enamel. To help prevent tooth decay many types of toothpaste contain basic substances to neutralize the acids produced by these bacteria in your mouth. The pH of these basic substances is alkaline (higher than 7). The pH of saliva is slightly alkaline (pH 7.4), so it can also help to counteract the acid, particularly after a meal. After eating a sweat, for example, it takes about 15 minutes for saliva to raise the pH above 5.8, and stop further decay.
especially sugary food is acted upon by bacteria in your mouth. The pH of a sugar solution is 7. However, bacteria in your mouth break down the sugar in plaque to form acids, for example lactic acid. These acids lower the pH. Tooth decay begins when the pH falls below 5.8. The acid attacks the tooth enamel. To help prevent tooth decay many types of toothpaste contain basic substances to neutralize the acids produced by these bacteria in your mouth. The pH of these basic substances is alkaline (higher than 7). The pH of saliva is slightly alkaline (pH 7.4), so it can also help to counteract the acid, particularly after a meal. After eating a sweat, for example, it takes about 15 minutes for saliva to raise the pH above 5.8, and stop further decay.
4. Soil treatment Most plants grow best when pH of the soil is close to 7. They prefer
the pH of between 6.5 and 7.0. If the soil pH is below 6.0, the soil is too acidic. Above
the pH of 8.0, the soil is too alkaline. If the soil is too acidic or too alkaline, the plants
grow poorly or not at all. Chemicals can be added to the soil to adjust its pH. Most
often, if the soil is too acidic, it is usually treated by liming. In this context, liming
means addition of quicklime (calcium oxide), slaked lime (calcium hydroxide) or
powdered chalk or limestone (calcium carbonate) to an acidic soil. These compounds
(bases) have the effect of neutralizing the acidity of the soil.
the pH of between 6.5 and 7.0. If the soil pH is below 6.0, the soil is too acidic. Above
the pH of 8.0, the soil is too alkaline. If the soil is too acidic or too alkaline, the plants
grow poorly or not at all. Chemicals can be added to the soil to adjust its pH. Most
often, if the soil is too acidic, it is usually treated by liming. In this context, liming
means addition of quicklime (calcium oxide), slaked lime (calcium hydroxide) or
powdered chalk or limestone (calcium carbonate) to an acidic soil. These compounds
(bases) have the effect of neutralizing the acidity of the soil.
If the soil is too alkaline, acids such as sulphuric acid, nitric acid or hydrochloric acid
may be added to the soil to neutralize excessive alkalinity. However, these compounds
are very expensive and hence uneconomical to apply on large-scale
may be added to the soil to neutralize excessive alkalinity. However, these compounds
are very expensive and hence uneconomical to apply on large-scale
5. Insect stings treatment When a bee stings someone, it injects an acid liquid into the
skin. The bee sting, which is acidic in nature, can be neutralized by rubbing on calamine
solution, which contains zinc carbonate or baking soda, which is sodium
hydrogencarbonate. These compounds are basic in nature and so have the effect of
neutralizing the acid in the sting. Wasp stings are alkaline in nature, and can be
neutralized with vinegar, which contains ethanoic acid. Ant and nettle stings
contain methanoic acid. These may be neutralized by rubbing an extract
squeezed from crushed onion leaves (which contain basic compounds)
on the affected skin. The acid in the sting can also be neutralized by applying
weak alkalis such as ammonia solution, ash extract, baking powder, etc.
skin. The bee sting, which is acidic in nature, can be neutralized by rubbing on calamine
solution, which contains zinc carbonate or baking soda, which is sodium
hydrogencarbonate. These compounds are basic in nature and so have the effect of
neutralizing the acid in the sting. Wasp stings are alkaline in nature, and can be
neutralized with vinegar, which contains ethanoic acid. Ant and nettle stings
contain methanoic acid. These may be neutralized by rubbing an extract
squeezed from crushed onion leaves (which contain basic compounds)
on the affected skin. The acid in the sting can also be neutralized by applying
weak alkalis such as ammonia solution, ash extract, baking powder, etc.
6. Factory wastes treatment Liquid wastes from factories often contain acid.
If it reaches a river, lake or ocean, the acid will kill fish and other aquatic life.
This can be prevented by adding slaked lime (calcium hydroxide) to the waste,
to neutralize the acid before being dumped into water bodies.
If it reaches a river, lake or ocean, the acid will kill fish and other aquatic life.
This can be prevented by adding slaked lime (calcium hydroxide) to the waste,
to neutralize the acid before being dumped into water bodies.
8. (a) Two chemicals that can be used to produce oxygen, hydrogen and carbon
dioxide in the laboratory are listed against respective gases below:
dioxide in the laboratory are listed against respective gases below:
(i) Oxygen: hydrogen peroxide and potassium chlorate. (ii) Hydrogen: Zinc
and dilute hydrochloric acid. (iii) Carbon dioxide: dilute hydrochloride acid and
marble (calcium carbonate).
and dilute hydrochloric acid. (iii) Carbon dioxide: dilute hydrochloride acid and
marble (calcium carbonate).
(b) Suitable indicators for the following titrations are as follows:
(i) Hydrochloric acid against ammonia solution (strong acid against weak base):
Methyl orange
Methyl orange
(ii) Sulphuric acid against sodium hydroxide solution (strong acid against strong
base): Any indicator may be used.
base): Any indicator may be used.
(iii) Ethanoic acid against potassium hydroxide solution (weak cid against strong base):
Phenolphthalein.
Phenolphthalein.
9 (a) (i) a chemical bond formed between fluorine atoms in a fluorine molecule is called
covalent bond.
covalent bond.
(ii) Fluorine can also form bonds with other elements. It forms covalent bonds with other
non metals, e.g., the bond between fluorine and hydrogen in the compound hydrogen
fluoride (HF). Other examples of compounds in which chlorine forms a covalent bond
include the following:
non metals, e.g., the bond between fluorine and hydrogen in the compound hydrogen
fluoride (HF). Other examples of compounds in which chlorine forms a covalent bond
include the following:
- Carbon tetraflouride, also known as
tetrafluoromethane (CF4) - Boron trifluoride (BF3) - chlorine pentafluoride (ClF5)
tetrafluoromethane (CF4) - Boron trifluoride (BF3) - chlorine pentafluoride (ClF5)
Fluorine also forms electrovalent bonds with metals. For example,
it forms an electrovalent bond with potassium in the compound potassium fluoride (KF).
Other compounds in which fluorine forms an electrovalent bond include the following:
it forms an electrovalent bond with potassium in the compound potassium fluoride (KF).
Other compounds in which fluorine forms an electrovalent bond include the following:
- Manganese difluoride (MnF2) - Iron trifluoride (FeF3) - Cobalt difluoride (CoF2) -
Nickel difluoride (NiF2) - Copper difluoride (CuF2)
Nickel difluoride (NiF2) - Copper difluoride (CuF2)
(b) (i) Element C H Cl % Composition 24.24 4.04 71.72
Atomic weight 12 1 35.5 Mole ratio 24.24 = 2.02
Atomic weight 12 1 35.5 Mole ratio 24.24 = 2.02
12
4.04 = 4.04 171.72 = 2.02 35.5 Relative molar ratio 2.02 = 1
2.02
4.04 = 2 2.02
2.02 =1 2.02
Empirical formula = CH2Cl
Given that the vapour density is twice the molecular formula, then
(CH2Cl) n = 49.5 × 2
49.5n = 99 n = 2 i.e. (CH2Cl)2 = C2H4Cl2
The molecular formula of compound X = C2H4Cl2
(ii) The open structural formula and the possible isomers of the compound C2H4Cl2
(dichloroethane) are shown below:
(dichloroethane) are shown below:
1,1-dichloroethane
1,2-dichloroethane
10. (a) (i) Samples A and D contain hard water because they don’t form lather with soap.
(ii) Sample A contains temporary hard water because this hardness is removed by
boiling water. In addition, sample D contains permanent hard. This type of water
hardness is not removed by merely boiling the water.
(ii) Sample A contains temporary hard water because this hardness is removed by
boiling water. In addition, sample D contains permanent hard. This type of water
hardness is not removed by merely boiling the water.
(b) Sub-atomic particle
Relative mass Relative charge Location in atom
Proton 1 unit + 1 in the nucleus Neutron 1 unit 0 in the nucleus Electron 1 1840
( almost nothing ) -1 outside the
nucleus
11. (a) Given: Current (I) passed = 2A Time (t) = 9 minutes (540 seconds) Mass (m) of
element X liberated = 0.3552 g Required: To find the molar mass of X
element X liberated = 0.3552 g Required: To find the molar mass of X
Solution: Charge flow (Q) = I × t
Q = 2 × 540
= 1080 coulombs
During electrolysis, X2+ ions move to the cathode and are discharged thus:
X2+(aq) + 2e- → X(s)
This shows that 2 moles of electrons (2 Faradays = 2 × 96500 = 193000 coulombs)
are required to deposit one mole of X.
are required to deposit one mole of X.
Now, if a charge of 1080 coulombs deposits 0.3552 g, then 193000 coulombs will deposit:
193000 1080× 0.3552 = 63.476 = 63.5 g/mol Therefore, the molar mass
of metal X = 63.5 g mol-1.
of metal X = 63.5 g mol-1.
(b) (ii) Pentane (ii) 2,2-dimethylmethan-1-ol (iii) 3-methylbutanoic acid
11. The chief ores of iron are haematite, an impure iron (III) oxide, Fe2O3,
which contains about 70% of iron; magnetite (or magnetic iron ore), triiron tetraoxide,
Fe3O4, which contains 72.4% of iron; and spathic iron ore, iron (II) carbonate, FeCO3.
It also occurs as limonite, Fe2O3.xH2O and as the sulphide in iron pyrites, FeS2.
However, though abundant in the earth’s crust, iron pyrite is not used a source of iron.
It is mainly used in the production of sulphuric acid.
which contains about 70% of iron; magnetite (or magnetic iron ore), triiron tetraoxide,
Fe3O4, which contains 72.4% of iron; and spathic iron ore, iron (II) carbonate, FeCO3.
It also occurs as limonite, Fe2O3.xH2O and as the sulphide in iron pyrites, FeS2.
However, though abundant in the earth’s crust, iron pyrite is not used a source of iron.
It is mainly used in the production of sulphuric acid.
To extract iron from its ores, three substances are needed: 1. Iron ore: The chief ore is
haematite. It is mainly iron (III) oxide, Fe2O3 mixed with
haematite. It is mainly iron (III) oxide, Fe2O3 mixed with
sand. 2. Limestone: This is mainly calcium carbonate, CaCO3. 3. Coke: This is made
from coal and is almost pure carbon.
from coal and is almost pure carbon.
The extraction of iron takes place in a structure called the blast furnace.
The blast furnace is a cylindrical tower like structure about 25m to 35m high. It has an outer shell of steel. Inside of furnace is lined with fire bricks. The top of the furnace is closed by a cup-cone feeder.
The blast furnace is a cylindrical tower like structure about 25m to 35m high. It has an outer shell of steel. Inside of furnace is lined with fire bricks. The top of the furnace is closed by a cup-cone feeder.
The extraction of iron in a blast furnace Before being introduced into the blast furnace,
all forms of iron ore must be converted to the oxide, Fe2O3,
by roasting in air.
4FeCO3(s) + O2(g) →2Fe2O3(s) + 4CO2(g) 4FeS2(s) +11O2(g) →2Fe2O3(s) + 8SO2(g)
all forms of iron ore must be converted to the oxide, Fe2O3,
by roasting in air.
4FeCO3(s) + O2(g) →2Fe2O3(s) + 4CO2(g) 4FeS2(s) +11O2(g) →2Fe2O3(s) + 8SO2(g)
Iron ore, coke and limestone are mixed together to give a mixture called charge.
The charge is introduced into a tall tower called a blast furnace (figure 8.2).
At the bottom of the furnace, hot air is blasted in through several pipes known as tuyeres.
A well at the bottom of the furnace serves to hold the molten iron and slag until these can
be run off. The charge is fed in continuously from the top.
The charge is introduced into a tall tower called a blast furnace (figure 8.2).
At the bottom of the furnace, hot air is blasted in through several pipes known as tuyeres.
A well at the bottom of the furnace serves to hold the molten iron and slag until these can
be run off. The charge is fed in continuously from the top.
Reactions that occur in the furnace 1. At the bottom of the furnace where temperature
is the highest, air attacks the coke
is the highest, air attacks the coke
to produce carbon dioxide.
C(s) + O2(g) →CO2(g)
2. In the middle of the furnace, the rising up carbon dioxide gas is reduced by more
coke, producing carbon monoxide. C(s) + CO2(g) →2CO(g)
3. At the top of the furnace, carbon monoxide reduces iron (III) oxide to metal.
Fe2O3(s) + 3CO(g) →2Fe(s) + 3CO2(g)
The molten iron trickles down the furnace and gathers at the bottom. Periodically,
this molten iron is tapped off and run into moulds (or containers), where it is allowed
to cool in long bars of about 1 metre long and 10 cm in diameter. At this stage,
it is called ‘cast iron’ or ‘pig iron’. The hot waste gases, mainly nitrogen and
oxides of carbon, escape from the top of the furnace and are used to heat incoming air.
This helps to reduce the energy costs of the process.
this molten iron is tapped off and run into moulds (or containers), where it is allowed
to cool in long bars of about 1 metre long and 10 cm in diameter. At this stage,
it is called ‘cast iron’ or ‘pig iron’. The hot waste gases, mainly nitrogen and
oxides of carbon, escape from the top of the furnace and are used to heat incoming air.
This helps to reduce the energy costs of the process.
Figure 8.2 The Blast furnace
Action of limestone The limestone, which is introduced together with the ore,
is first decomposed at this high temperature to form calcium oxide.
CaCO3(s) → CaO(s) + CO2(g) The main impurity in iron ore is sand,
made of silicon dioxide (SiO2). This reacts with calcium oxide to form calcium silicate.
CaO(s) + SiO2(s) →CaSiO3(l) The calcium silicate, which is in liquid state,
falls to the bottom of the furnace. This liquid, called slag (because
it is less dense than the molten iron) is tapped off separately.
Slag is a useful by-product. It is used for making roads, production of cement,
and as a fertilizer.
is first decomposed at this high temperature to form calcium oxide.
CaCO3(s) → CaO(s) + CO2(g) The main impurity in iron ore is sand,
made of silicon dioxide (SiO2). This reacts with calcium oxide to form calcium silicate.
CaO(s) + SiO2(s) →CaSiO3(l) The calcium silicate, which is in liquid state,
falls to the bottom of the furnace. This liquid, called slag (because
it is less dense than the molten iron) is tapped off separately.
Slag is a useful by-product. It is used for making roads, production of cement,
and as a fertilizer.
12. Addition of inorganic fertilizers in the farm is NOT as important as
addition of organic manure.
Organic manure has several advantages which make it suitable over inorganic (synthetic)
fertilizers. Outlined below are the advantages of organic manure and disadvantages
of inorganic fertilizers:
Advantages of organic manure 1. They add nutrients to the soil and at the same time addition of organic manure.
Organic manure has several advantages which make it suitable over inorganic (synthetic)
fertilizers. Outlined below are the advantages of organic manure and disadvantages
of inorganic fertilizers:
improve soil physical properties such as soil colour, soil structure and water holding
capacity of the soil. A soil with good content of organic matter (supplied by manure)
holds water and dissolved nutrients efficiently making them available to crop plants.
hot air
iron ore, coke and limeston
slag
tapped here
brick lining
1000°C
1500oC
2000oC
Fe3O4 + 4CO
3Fe + 4CO2
CO2 + C → 2CO
C + O2 → CO2
iron tapped here
waste gases to heat up
tuyeres
2. Manures supply humus to soil which, in turn, increases the cation exchange
capacity of the soil. Humus accounts for 30–90% of the cation exchange
capacity of mineral soils. And because of its high cation exchange capacity,
humus helps to store nutrient cations, especially ammonium ions, thus
reducing the leaching of these nutrients from the soil.
capacity of the soil. Humus accounts for 30–90% of the cation exchange
capacity of mineral soils. And because of its high cation exchange capacity,
humus helps to store nutrient cations, especially ammonium ions, thus
reducing the leaching of these nutrients from the soil.
3. Manures improve the proliferation of the soil macro- and microorganisms by
supplying the nutrients and conducive conditions needed by these organisms for
survival. These organisms play a vital role in soil fertility and plant nutrition by
decomposing organic matter which releases nutrients to the soil.
supplying the nutrients and conducive conditions needed by these organisms for
survival. These organisms play a vital role in soil fertility and plant nutrition by
decomposing organic matter which releases nutrients to the soil.
4. Manures provide organic matter which acts as the binding materials for soil
particles, making them more compact and hence resistant to the impact of rain
drops and surface run off of water. Thus, it reduces soil erosion.
particles, making them more compact and hence resistant to the impact of rain
drops and surface run off of water. Thus, it reduces soil erosion.
Disadvantages of inorganic fertilizers 1. They are used only for one growing season
as they are short-lived. Because the uptake of the nutrients in the fertilizer is very high,
no or few nutrients would have remained in the soil in the next growing season.
as they are short-lived. Because the uptake of the nutrients in the fertilizer is very high,
no or few nutrients would have remained in the soil in the next growing season.
2. Some acidic mineral fertilizer such as NH4 and (NH4)2SO4 contribute to soil acidity.
When these fertilizers are applied to the soil repeatedly, they can make the soil acidic
and hence not fit for plant growth.
When these fertilizers are applied to the soil repeatedly, they can make the soil acidic
and hence not fit for plant growth.
3. Prolonged use of artificial fertilisers may lead to deterioration of the soil structure,
soil and microbial poisoning and contamination of drinking water resources,
by especially nitrate fertilizers. Nitrates dissolved in water are not removed
by normal purification processes. In the body nitrates may be converted into
nitrosamines. These are carcinogenic (cancer-causing) compounds.
soil and microbial poisoning and contamination of drinking water resources,
by especially nitrate fertilizers. Nitrates dissolved in water are not removed
by normal purification processes. In the body nitrates may be converted into
nitrosamines. These are carcinogenic (cancer-causing) compounds.
4. If too much nitrogenous fertilizer is used, serious pollution can occur.
One kind of pollution is called eutrophication. Excess of the fertilizer applied
finally finds its way to water. This encourages fast growth and huge increase
in the number of microscopic plants called algae, a phenomenon called algal
bloom. Proliferation of algae on the water surface blocks sunlight from reaching
the plants beneath the water. These plants can not carry out photosynthesis and,
therefore, they die. Bacteria and other decomposers feed on these dead plants
and increase in number. These decomposers use up all the oxygen dissolved in
the water. Without supply of oxygen fish and other organisms living in the water die.
One kind of pollution is called eutrophication. Excess of the fertilizer applied
finally finds its way to water. This encourages fast growth and huge increase
in the number of microscopic plants called algae, a phenomenon called algal
bloom. Proliferation of algae on the water surface blocks sunlight from reaching
the plants beneath the water. These plants can not carry out photosynthesis and,
therefore, they die. Bacteria and other decomposers feed on these dead plants
and increase in number. These decomposers use up all the oxygen dissolved in
the water. Without supply of oxygen fish and other organisms living in the water die.
5. They can burn and kill crop plants if not applied under manufacture’s directions or
even harm humans if not properly handled.
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