Carbon is the sixth element in
the periodic table, found in period II group IV. It has an electronic
configuration of 1s22s22p4.
OCCURRENCE
As a free element it occurs naturally as diamond, graphite, graphene and Fullerene in the crystalline forms. It occurs in non crysatlline forms as coal, Coke, carbon black, soot
and charcoal. It also occurs in the combined state as petroleum,
wood and natural gases, in minerals such as limestone (CaCO3)
and dolomite (MgCO3), in the atmosphere as CO2 and present as a main constituent in all plants and animals.
ALLOTROPES
OF CARBON
Allotropy is the phenomenon whereby an
element exists in two or more different forms in the same physical state.
The
different forms of the elements are known as allotropes.
Allotropes have the same
chemical properties but different physical properties.
Carbon exists in several allotropic forms:
1. Crystalline allotropes of carbon
i. Diamond
ii. Graphite
iii. Fullerenes
iv. Grephenes
(2). Non-crystalline Allotropes/Amorphous
carbon
i. Coal,
ii. Charcoal
iii. Coke
iv. Lampblack and
v. Carbon black (soot)
Crystalline
Allotropes of carbon
Diamond: Diamond is the purest form of
carbon. In diamond each carbon atom is tetrahedrally bonded ( bonded on the four sides). The carbon atoms are closely parked and held by strong covalent bonds resulting to a giant
molecule with an octahedral shape
Basic Tetrahedral Shape in Diamond
Crystals
PROPERTIES OF DIAMOND
(1) It is the hardest substance know
(2) It has a high melting and
boiling point because of strong covalent bond.
(3) It has a high density
(4) It is a very resistant to
chemical action and temperature because all four valence electrons are
saturated bonded.
(5) It is a non-conductor of
electricity because there are no free valence electrons in the crystal
(6) It is transparent and high refractive index( it has the abilityto
scatter light.)
USES
(1) The are used industrially for making drilling machines
(2) They are used to sharpen very hard tools.
(3) They are used for cutting glass and metals.
(4) They are also used as pivot supports in precision instruments
and as dies for drawing wires
(5) They are used as jewellery
Artificial diamond: They are made by subjecting graphite to a very
high temperature and pressure for several hours in the presence of nickel or
rhodium catalyst.
GRAPHITE: In graphite the carbon
atoms uses only 3 out of its 4 valence electrons for bonding forming flat
hexagonal layers. These hexagonal layers are arranged one above the other to
form a crystal lattice, each layer is bonded by weak van der walls forces of
attraction.
PROPERTIES OF GRAPHITE
(1) Graphite is soft and slippery because of weak forces holding its
layers. Each layer can slide over one another. Hence, graphite acts as a
lubricant.
(2) It is less dense than diamond
(3) It is not affected by chemical attack (due to its open structures in
layers).
(4). It is a good conductor of electricity (because of the presence
of free delocalized electrons (mobile electron) in the crystal lattice.)
(5) It has high melting and boiling point.
USES
(1) It is usually used on bicycle chains and for the bearings of
some motor cars.
(2) It is used as a dry lubricant.
(3) It is used as electrodes in electroplating and in dry cells.
(4) It is used to line crucibles for making high-grade steel and
other alloys (since it can withstand high temperature).
(6) It is used in making lead pencils i.e. combining it with clay
makes lead in pencils.
(7) It is used as a black pigment in paints.
(8) It is used as a neutron moderator in atomic piles.
INDUSTRIAL PREPARATION OF
GRAPHITE
Graphite is produced industrially by heating coke in an electric
furnace to a very high temperature for about 20 to 30 hours in the absence of
air and under sand. This process is called the Acheson process. The graphite
produced is very pure and free from grit.
DIFFERENCES IN PROPERTIES
BETWEEN GRAPHITE AND DIAMOND
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Graphite
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Diamond
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1. It has a density of 2.3gcm-3
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1. It has a density of 3.5gcm-3
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2. It is a black, opaque solid
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2. It is a colourless, transparent solid
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3. It is very soft, marks paper
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3. It is the hardest known substance.
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4. It is a good conductor of electricity
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4. It is a non-conductor of electricity
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5. Attacked by potassium trioxochlorate (v) and trioxonitrate (v)
acid together.
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5. Not attacked by these reagents.
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Note: Diamond is transparent to x-rays while glass is almost opaque.
⚽ Fullerenes
Fullerenes (e.g. C60) are spherical carbon molecules called buckyballs. They are used in medicine, electronics and materials science.
AMORPHOUS CARBON
These non-crystalline structures which are not considered to be true
allotropes include:
CHARCOAL: This is made by burning wood, bones, or sugar in a limited
supply of air. Charcoal is used to
remove colour from substances. Wood charcoal is used in absorbing poisonous
gases while animal charcoal is used in absorbing colours.
CARBON BLACK AND LAMP BLACK: Lamp black is obtained by burning
vegetable oil lamp that it leaves a deposit of soot while carbon black is obtained from burning
coal gas, natural gas or petroleum.
Carbon black and lamp black are used as an
additive to rubber tyres. They are also used in making printer’s ink, carbon
paper, black shoe polish, type writing.
COAL
Coal is an impure form of carbon. Coal is a complex mixture of
compounds composed mainly of carbon, hydrogen and oxygen with small amounts of
nitrogen, sulphur and phosphorus as impurities.
Carbonization of coal.
Coal was formed by the gradual decomposition of plant vegetation
under pressure and in the absence of air under sand. A time known as the carboniferous Era. Carbon (iv)
oxide, methane, and steam were liberated, leaving behind a material that
contained a very high percentage of carbon.
During this process of carbonization, the vegetable material was
converted in stages into several stages of coal namely
Types of Coal
There are 4 different types of coal namely:
(1) Peat-like coal: It contains about 60% of carbon by mass.
(2) Lignite coal (brown coal): It contains about 67% of carbon by
mass.
(3) Anthracite coal (or hard coal): It is tough and hard. It
contains about 94% of carbon by mass. Impurities present may include nitrogen,
sulphur and phosphorus. Anthracite is the last stage of coal.
(4) Bituminous (soft) coal: These are use every day at home. It
contains about 88% by mass of carbon.
Destructive Distillation
of Coal
This is when coal is heated to a very high temperature in the
absence ofair.
Yielding the following products
Coal Coal gas + Coal tar Ammoniacal liquor + Coke
Uses of coke
(i) Coke is mainly used as a fuel.
(ii) It is a very important industrial reducing agent and is used in
the extraction of metals, especially iron, from their ores.
(iii) It is also used in the production of gaseous fuels, like water
gas and producer gas.
(iv) It is used for the manufacture of graphite, calcium carbide,
silicon carbide and carbon (iv) sulphide.
2.
(a) Coal gas: used mainly as industrial fuel
(b) Ammoniacal liquor: is a solution of NH3 in water. It
is used to make Fertilizers
(C) Coal tar :- it is used for road construction and also to produce
other chemicals like toluene, phenol, benzene, naphthalene and anthracene which
are used in the synthesis of important commercial product like dyes, paints,
insecticides, drugs, plastics and explosives
(d) Coke :
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Distillates of Coal
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Uses
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1.Ammoniacal liquor
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To produce (NH4)2SO4 for
fertilizer.
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2.Coal tar
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To produce useful chemicals such as phenol, benzene, disinfectants and perfumes
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3.Coal gas
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Used as industrial fuel.
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Uses of coal
1. Coal is used mainly as
fuel to generate power for steam engines, factories and electrical plants.
2. It is also used
FUEL GASES/GASIFICATION OF
COKE
There are 3 types of fuel gases.
1. Producer gas: Producer gas is a mixture of nitrogen and carbon (ii)
oxide. It is prepared by passing a stream of air through red hot coke.
2C(s)h +
O2(g) + N2(g) → 2CO(g) +
N2(g) + Heat
Producer gas
2. Water gas: Water gas is a mixture of hydrogen and carbon (ii)
oxide gas. It is prepared by passing steam over white hot coke.
H2O(g) +
C(s) → CO(g) +
H2(g)
Steam white hot
coke Water gas
2. Hydrogen gas:-water gas is
then mixed with excess steam, and the mixture passed over iron (iii) oxide
catalyst at 4500C.The carbon (ii) oxide decomposes the steam and the
product are hydrogen and carbon (iv) oxide.
CO(g) + H2(g) +
H2O(g) → CO2(g) + 2H2(g)
Caustic soda or water is used to absorbed carbon (iv) oxide from the
mixture. Ammoniacal copper (i) chloride can be used to remove unreacted carbon
(ii) oxide. The final product is hydrogen.
Differences between
Producer Gas and Water Gas
(1) Producer gas has a lower heating ability than water gas. (
because water gas consists of equal volumes of hydrogen and carbon (ii) oxide both of which are
combustible whereas producer gas consists of 33% combustible CO and 67%
non-combustible N2.
Water gas is an important industrial fuel and is used in the
manufacture of hydrogen and other organic compounds e.g. methanol and butanol.
3. Synthetic gas: It is a
mixture of hydrogen and carbon (ii) oxide gas. It is prepared by mixing steam
with methane (obtained as natural gas) and passing them over Nickel catalyst at
about 8000C.
CH4(g) +
H2O(g) → CO(g) + 3H2(g)
Synthetic gas is not a major source of air pollution because sulphur
is removed in the gasification process/it does not contain sulphur or sulphur
compounds.
CHEMICAL PROPERTIES OF
CARBON
(1) Combustion:
(a) All forms of carbon burn in excess oxygen to produce carbon (iv)
oxide gas.
C(s) +
O2(g) → CO2(g) ( Complete combustion)
(b) All forms of carbon also burn in a limited supply of air to
produce carbon (ii) oxide.
C(s) +
O2(g) → CO(g) ( Incomplete combustion)
(2) Combination reaction: Carbon combines directly with certain
elements such as Sulphur, Hydrogen, Calcium and Aluminum at very high
temperatures.
C(s) + 2S(s) → CS2(l)
Carbon (iv) sulphide
C(s) + 2H2(g) → CH4(g)
Methane
2C(s) +
Ca(s) → CaC2(s)
Calcium carbide
3C(s) + 4Al(s) → Al4C3(s)
Aluminium carbide.
(3) As a reducing agent: Carbon is a strong reducing agent. It
reduces the oxides of the less active metals to the metals, while carbon is
itself oxidized to either carbon (iv) oxide or carbon (ii) oxide, depending on
the reaction conditions.
Fe2O3(s) +
3C(s) → 2Fe(s) + 3CO(g)
2CuO(s) + C(s) → 2Cu(s) + CO2(g)
(4) Reaction with strong
oxidizing agents: When carbon is heated with conc. HNO3 or conc. H2SO4,
it is oxidized to Carbon (iv) oxide.
C(s) +
4HNO3(aq) →2H2O(l) + 4NO2(g) + CO2(g)
C(s) +
2H2SO4(aq) → 2H2O(l) + 2SO2(g) + CO2(g)
TOPIC: OXIDE OF CARBON.
CONTENT
·
Carbon (iv) oxide
·
Carbon (ii) oxide
CARBON (iv) OXIDE:- Carbon (iv) oxide is present in the atmospheric air about 0.03% by volume
while in dissolved air is about 0.50% by volume.
Laboratory preparation
Carbon (iv) oxide is
prepared in the laboratory by the action of dilute acids on a trioxocarbonate
(iv) or a hydrogen trioxocarbonate (iv). Usually CaCO3, in form of
marble chips is used with hydrochloric
acid. Reaction between CaCO3 and HCl can be carried out in a Kipp’s
apparatus.
CaCO3(s) +2HCl(aq) → CaCl2(aq) + H2O(l)
2. It is also prepared by
heating metallic trioxocarbonates (iv) [except those of Na and K], or the
hydrogen trioxocarbonate (iv) of Na or K.
CuCO3(s) → CuO(s) + CO2(g)
Note: If the gas is
required dry, it is pass through
potassium hydrogen trioxocarbonate (iv) solution first to remove any acid
fumes, and then through a U-tube containing fused Calcium chloride to remove
the water vapour. The dry gas is then collected by downward delivery as it is
heavier than air.
Method of collection of gases
The method of collection
of gases depends on its:
1. Density.
2. Solubility.
There are two method of
collecting gases:
(a) Downward
delivery/upward displacement of air: This method is used for collecting gases
that are denser than air e.g. CO2, SO2, H2S,
NO2, Cl2 and HCl e.t.c.
(b) Upward
delivery/downward displacement of air: This method is used for collecting gases
that are less denser than air e.g NH3, H2, N2,
methane and ethane.
INDUSTRIAL PREPARATION
CO2 is
obtained industrially as a by product in fermentation processes and when
limestone is heated to make quicklime.
PHYSICAL PROPERTIES
(1) CO2 is a
colourless, odourless gas with a sharp refreshing taste.
(2) It is about 1.5 times
denser than air.
(3) It is soluble in
water.
(4) It turns damp blue
litmus paper pink because CO2 dissolves in water to yield
trioxocarbonate (iv) acid.
(5) On cooling, it
readily liquefies and solidifies (-780C) to form a white solid known
as dry ice.
CHEMICAL PROPERTIES
1. Reaction with water:
Carbon (iv) oxide is not very active chemically. It dissolves in water to form
trioxocarbonate (iv) acid (Soda water). This is a weak, dibasic acid which
ionizes slightly.
(a)
CO2(g) + H2O(l) → H2CO3(aq)
(b)
H2CO3(aq) + H2O(l) → H3O+(aq) + HCO3-(aq)
On heating,
trioxocarbonate (iv) acid decomposes to form H2O(l) and
CO2(g).
2. Reaction with alkalis:
It reacts directly with alkalis to yield trioxocarbonate (iv)
CO2(g) + 2NaOH(aq) → Na2CO3(aq) + H2O(l)
Limited
Excess CO2
reacts with alkalis to produce Hydrogen trioxocarbonate (iv) salt.
CO2(g) + NaOH(aq) → NaHCO3(aq)
Excess.
3. Reaction with burning Na, K or Mg: CO2
is reduced to carbon by burning Na, K or Mg.
CO2(g) + 2Mg(s) → C(s) + 2MgO(s)
Note: CO2 does not support combustion.
4. Reaction with red hot
carbon: CO2 is reduced to CO, If the gas is passed over red hot
carbon.
CO2(g) + C(s) → 2CO(g)
The reaction is of great importance in the blast furnace and in the
manufacture of gaseous fuels.
Test for CO2: Bubble the unknown gas through a solution of lime water (Calcium
hydroxide)if the lime water turn milky due to the formation of insoluble
calcium trioxocarbonate (iv), then the unknown gas is CO2
Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l).
If the gas is bubbled in excess, the milkiness disappears and turns
to a clear solution due to the formation of soluble calcium hydrogen
trioxocarbonate (iv).
CaCO3(s) +
H2O(l) + CO2(g) → Ca(HCO3)(aq)
Finally, if the clear solution is heated, the
milkiness reappears due to the decomposition of soluble Ca(HCO3)2
to form insoluble CaCO3
Ca(HCO3)2(aq)→ CaCO3(s) + H2O(l) + CO2(g)
Uses of carbon (iv) oxide
1. It is used as fire
extinguishers since it does not support combustion.
2. It gives carbonated
(aerated) drinks their refreshing taste. Beer, cider and champagne contains CO2
3. It is used in the
manufacture of Na2CO3 (washing soda) by the Solvay
process.
4. It is used as a leavening
agent in the baking of bread. Yeast and baking powder produces CO2
which make the dough of bread to rise.
5. It is used in the
manufacture of fertilizer (such as urea and (NH4)2SO4.
6. Solid CO2 (i.e
dry ice) is used as a refrigerant for perishable goods e.g ice cream. (It
sublimes on warming and provides a lower temperature).
7. Gaseous CO2 is
used to preserve fruits.
8. CO2 is also
used as a coolant in nuclear reactors.
CARBON (II) OXIDE
LABORATORY PREPARATION
1. Carbon (ii) oxide can be
prepared by passing Carbon (iv) oxide through red-hot carbon while the Carbon
(iv) oxide is itself reduced to Carbon (ii) oxide. The gaseous mixture is
passed through concentrated NaOH to remove the excess Carbon (iv) oxide.
CO2(g) + C(s) → 2CO(g)
The pure Carbon (ii) oxide is collected over water.
2. Carbon (ii) oxide can also
be prepared by the dehydration of methanoic (formic) acid or ethanedioic
(oxalic) acid, using concentrated tetraoxosulphate (vi) acid.
HCOOH(l) →Conc. H2SO4 CO(g) + H2O
Methanoic acid
Note: The gaseous mixture is passed through concentrated NaOH to
remove the CO2.
Caution: The preparation of CO must be done in a fume cupboard as
the gas is poisonous.
The major air pollutants that can result from smoky vehicles are
Carbon (ii) oxide and Carbon particles.
When CO is breath in for any length of time, even 1% of it in the
air may cause death, by suffocation.
PHYSICAL PROPERTIES OF CO
(1) CO is a poisonous, colourless, tasteless and odourless gas.
(2) It is insoluble in water, but dissolves in a solution of
ammoniacal copper (i) chloride.
(3) It is neither lighter nor heavier than air.
(4) It is neutral to litmus.
CHEMICAL PROPERTIES OF CO
(1) As a reducing agent: CO is a strong reducing agent. It reduces
some metallic oxides to the metals and it is oxidized to CO2.
Fe2O3(s) + 3CO(g) →2Fe(s) + 3CO2(g)
CuO(s) + CO(g) → Cu(s) + CO2(g)
2. Combination
reaction
(a). With oxygen: CO burns in air with a faint
pale blue flame to form CO2 .
2CO(g) + O2(g) → 2CO2(g)
(b).
With haemoglobin: CO combine irreversibly with haemoglobin in the red blood cells to form carboxy-haemoglobin
thereby preventing the red corpuscle from carry oxygen.
3j. CO
combined with Chlorine gas when expose to ultra-violet light or passed over a
catalyst of activated charcoal at 1500C to form carbonyl chloride.
CO(g) + Cl2(g) → COCl2(g)
This product, COCl2, is also known
as Phosgene and was employed as a poisonous gas in the First World War. It is
now use in the manufacture of dyestuff.
Test
for Carbon (ii) oxide
When a lighted splint is inserted into a test
tube containing CO(g) it
burns with a pale blue flame and the gas produced turns lime water milky.
Uses of
Carbon (ii) oxide
(1) CO is used in the extraction of metals
from their ores.
(2) It is also an important constituent of
gaseous fuels like producer gas and water gas.
(3) CO gas is used in the manufacture of
methyl alcohol, synthetic petrol, carbonyl chloride, oxalate and formate.
WEEKEND ASSIGNMENT
1. Kipp’s apparatus is important in the laboratory because it (a)
allows intermittent supply of gases. (b) is used for preparing poisonous gases.
(c) is used to prepare light gas. (d) is used to prepare sensitive gas
2. Gas prepared by the reaction between methanoic acid and
concentrated tetraoxosulphate (vi) acid is (a) SO2 (b) CO (c) CO2 (d) H2S.
3. Gas which dissolves in ammoniacal copper (i) chloride but
insoluble in water is
(a) NH3 (b) CO (c) N2O (d) CO2.
4. Where else is CO2 found in free state apart from the
atmosphere?
(a) In carbonated drinks. (b) Dissolved form in water. (c) In
corals. (d) In limestone region
5. It is dangerous to stay in a badly ventilated room which has a
charcoal fire because of the presence of (a) carbon (ii) oxide (b) carbon (iv)
oxide (c) hydrogen sulphide (d) producer gas.
THEORY
1(a) Why is the laboratory preparation of carbon (ii) oxide done in
a fume chamber?
(b) State the property of CO2 that makes it to be used in
(i) carbonated drinks (ii) fire extinguishers
2(a) Why it is not advisable to stay in a closed garage for a long
time when racing a car engine.
(b). State what is observed when (i) excess CO2 is
bubbled through lime water. (ii) the solution in b(i) above is heated.
TOPIC: TRIOXOCARBONATE (iv) ACID
H2CO3 is formed when CO2(g) is
dissolved in water. H2CO3 is a weak dibasic acid. It
forms two series of salts:
1. Normal trioxocarbonate (iv)
2. Acidic hydrogen trioxocarbonate (iv)
Normal trioxocarbonate
(iv)
Normal trioxocarbonate (iv) may be regarded as salts derived from H2CO3
by the complete replacement of the hydrogen by a metal or ammonium ion.
Preparation of soluble
trioxocarbonates (iv)
The CO32- of Na+, K+,
and NH4+ are soluble in water. They are prepared in the
laboratory by:
Bubbling CO2 through a solution of corresponding alkali.
2KOH(aq) +
CO2(g) K2CO3(aq) +
H2O(l)
Decomposition of corresponding hydrogen trioxocarbonates (iv).
2KHCO3(s) K2CO3(aq) +
H2O(l)
+ CO2(g)
Preparation of insoluble
trioxocarbonates (iv)
The insoluble metallic trioxocarbonates (iv) can be prepared by
adding a solution of Na2CO3 or NaHCO3 to a
solution of the corresponding metallic salt.
CaCl2(aq) + Na2CO3(aq) CaCO3(s) +
2NaCl(aq)
CaCl2(aq) +
2NaHCO3(aq) CaCO3(s) +
2NaCl(aq) + H2O(l) + CO2(g)
2AgNO3(aq) + Na2CO3(aq) Ag2CO3(s) +
2NaNO3(aq)
2AgNO3(aq) +
2NaHCO3(aq) Ag2CO3(s) +
2NaNO3(aq) + H2O(l)
Note: When preparing the CO32- of the less
electropositive metals like Cu, use NaHCO3
Properties of CO32-
Salts
Solubility: The trioxocarbonate (iv) of alkali metal and NH4+
are soluble while the other trioxocarbonate (iv) are insoluble in water.
Na2CO3(s) +
2H2O(l)
2NaOH(aq) + H2CO3(aq)
2. Action of heat: The
trioxocarbonate (iv) of Na, K and Barium cannot be decomposed by heat while all
other CO32- decompose on heating to liberate CO2.
ZnCO3(s) ZnO(s) + CO2(g)
2Ag2CO3(s) 4Ag(s) +
2CO2(g) + O2(g)
(NH4)2CO3(s) 2NH3(g) + CO2(g) +
H2O(l)
1.
Reaction with dilute acids: All
trioxocarbonates (iv) react with dilute acids to form CO2, H2O
and a salt.
Na2CO3(aq) + H2SO4(aq) → Na2SO4(aq) +
H2O(l)
+ CO2(g)
ZnCO3(s) +
2HCl(aq) ZnCl2(aq) + H2O(l) + CO2(g)
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Metal
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Solubility/effect of heat
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Reaction with acids
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K, Na
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Soluble in water. Does not decompose on heating
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These trioxocarbonate (iv) react with dilute acids to give a salt,
water and carbon (iv) oxide.
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Ca, Mg, Al, Zn
Fe, Sn
Pb, Cu
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Insoluble in water. Decompose to yield the oxide and carbon (iv)
oxide. Al2(CO3)3 does not exist.
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Hg, Ag
Au
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Insoluble in water. Decomposed to the metal, CO2 and
oxygen
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Test for any CO32-
The unknown substance is placed in a test-tube and dilute
trioxonitrate (v) acid is added into the test tube. If a CO32-
is present, there will be effervescence and the gas which evolved will turn
calcium hydroxide solution (lime water) milky.
CO32-(s) +
2H+(aq) H2O(l)
HYDROGEN TRIOXOCARBONATE
(iv).
HCO3- may also be regarded as salts derived
from H2CO3 by the partial replacement of the hydrogen by
a metal or cationic radical.
Preparation of HCO3-
HCO3- can be prepared by passing CO2
through a cold solution of the corresponding OH- or CO32-.
1. 2OH-(aq) +
CO2(g)
CO32-(aq) +
H2O(l)
2. CO32-(aq) +
CO2 (g) + H2O (l) 2HCO3-(aq)
Properties of HCO3-
1. Solubility: All hydrogen
trioxocarbonate (IV) are soluble in water.
2. Action of heat: They can
all be decomposed by heat.
2NaHCO3(s) Na2CO3(s) + H2O(l) +
CO2(g)
3. Reaction with dilute
acids: All HCO3- reacts with dilute acid to produce CO2,
H2O and a salt. 2NaHCO3 (aq) + H2SO4 (aq) Na2SO4(aq) +
2H2O(l)
+ 2CO2(g)
NOTE: This reaction is used to test for HCO3-
