CHE3: CARBON AND ITS COMPOUNDS

CARBON AND ITS COMPOUNDS

Carbon is a non metallic element of group four of the period table with atomic number of 6 and electronic configuration of 2:4

Valency is 4

The allotropes of carbon are;

Diamond          crystalline forms

Graphite

Amorphous carbon – non crystalline

Graphite

Structure of graphite

It has two dimensional hexagonal layer structure in which each carbon atom is covalently bonded to three other therefore 3 out of 4 of the valency electrons are used in bonding (localised). The remaining electron is decalised outer the whole structure.

Adjuscent layers are jined by weak vander waals forces of attraction.

The vander waals forces can break and adjuscent layers can slide relative to each  other. This explains why graphite is soft and slippery.

Uses of graphite

1. As a protective coating iron substances to prevent rusting.
2. Graphite conducts electricity because it contains mobile electrons (delocalized electrons) because of this property it is used as electrons in electrolysis and dry cells.
3. Graphite is soft and slippery because of this property it is used as lubricant in dynamos and electric mortars.

Also used in pencil lids (mixture of graphite and clay)

 Diamond

Structure of diamond

Diamond has a tetrahedral structure in which carbon atom is covalently bonded to four other atoms as shown in the figure above.

All the valency electrons of carbon are used in the formation of covalent bond, therefore, are localized. This explains why diamond s a non – conductor of heart and electricity. (it doesn’t have free mobile electrons).

Diamond has a giant structure in 3 dimensions. The strength of diamond and uniformity of bonding make it very hard, not volatile and resistant to chemical attack.

Structure of Graphite

Uses of diamond

1. Uses for drilling and cutting hard substances like glass. (this is because diamond is very hard)
2. Used in manufacture of necklaces, eartings etc bcause it has a sparkling appearance (high refractive index.)

Amorphous carbon

It is impure carbon it occurs in form of animal charcoal, wood, charcoal, soot coke, coal etc. it is make up  of sall crystals of graphite. It’s a black opaque solid.

Uses of amorphous carbon

It has a good absorption power and is used to purity substances especially solutions and gases. Impurities in solutions can be removed by boiling the solution with activities charcoal and filtering the mixture.

Granular amorphpous carbon has ability to absorb gases particularly the one of the most of the known toxic one.

The absorption property finds application in industries especially in sugr industry to remove the brown colour form sugar and in the manufacture of gas masks used in mine and by riot police.

Wood charcoal:

It is prepared by heating woon in absence of air so that it doesn’t burn. (distrctive distillation of wood.) it is used as fuel.

 Animal charcoal:

Prepared by distrcive distillation of bones. Heating in absence of air. To remove brown colour from sugar.

Coke:

 Is a form of carbon

Used as a fuel because it burns to liberate a lot of heat energy.

It is used as a reducing agent in the extraction of metals like iron

Lamp black (soot); obtained by burning oils.

Used for making printers ink and black shoe polish.

 

Properties of carbon

1. It burns in excess air. (excess oxygeb to form carbondioxide.)

Therefore, used as a fuel

• In limited air, carbon burns to give carbondioxide which is very poisonous
• Burning carbon in limited air produces poisonous carbondioxide that is a sources of pollution.

Never use charcoal stove in a closed room e.g charcoal will burn in limited air forming carbondioxide.

2. Carbon is used as a reducing aget to reduce some metal oxides.

Fuel;

is a substance which burns to give heat energy.

 Types of fuel

1. Solid fuel – charcoal, coal, fire wood, peat, coke.

They are either carbon or forms of  carbon.

1. Gaseous fuel- gas, biogas, hydrogen, water gas, producer gas.

Gas is a mixture of alkanes (carbon and hydrogen)

Disadvantages of using water gas as fuel

• It contains poisonous carbonmonoxide

Producer gas ;

it is a mixture of carbonomoxide and nitrogen.

 Disadvantages

• Poisonous carbonomoxide
• It contains nitrogen which is not combustible
• Liquid fuel; paraffin, petrol, diesel oil, ethanol, spirit.

 Criteria for a goo fuel (qualities).

• Should be able to purn liberating a lot of heat energy per unit mass.
• Should be readily available
• Should be easily transported with minimal fire risks.
• Should be easy to store.

• Environment effect; it shouldn’t cause a lot of pollution

Should burn easily without leaving a lot of solid residue

CARBON DIOXIDE

The biggest pool of carbon dioxide is in the atmosphere. It comprises of about 0.03% by volume of air.

T is also produced as waster product of respiration by plants and animals. It is also formed during combustion (burning) of fuels with contain carbon like charcoal, wood, petrol etc.

Some carbon dioxide occurs in solution in water like Lake Victoria, Kyoga, Albert.

 Bonding in carbon monoxide

The carbon atom is linked to two type’s oxyegsns each by double bonding

Laboratory preparation of carbon dioxide gas

Carbon dioxide is prepared byrecting calcium carbonate (in form of marble chips or limestone) with dilute or concentrated by hydrochloric acid as shown in the digram below

 Set up of apparatus for preparation of carbon dioxide gas

Calcium carbonate dissolves in the acid with effervescence evolving a colorless gas. Carbon dioxide which can be collected over water in which it is slightly soluble to give a weakly acidic solution.

Ionic equations

If required dry, the gas is bubbled through water to remove hydrogen chloride gas and then through concentrated sulphuric acid to dry it. It is then collected by down ward delivery. (Carbon dioxide is denser than air.)

Test for carbon dioxide

Chemical test

It is a colourless gas which turns blue litmus faint pink.

It turns lime water milky

Carnondioxide is weakly acidic

Carbon dioxide reacts with lime water (calcium hydroxide solution) to form a white precipitate calcium carbonate.

Note:

a combination of marble chips or (lime stone) with dilute sulphuric acid is not suitable for the laboratory preparation of carbon dioxide gas.

 Explanation

This is because marble chips or limestone react with dilute sulphuric acid to form insoluble calcium sulphate which stops further chemical reaction.

Therefore, reaction starts but stops after a short time.

In industries, carbon dioxide is obtained as a by – product of fermentation of sugars to 9alcohol and from the manufacture of cement.

 Fermentation

Is incomplete of sugars to ethanol, carbon dioxide and heat energy.

Cement is manufactured by heating limestone (calcium carbonate) with sand and silicates to form impure calcium oxide.

 Properties of carbon dioxide

Physical properties

It is slightly soluble in water forming carbonic acid

It turns blue litmus faint pink.

Colourlesss gas

Denser than air.

Chemical properties

Effect of carbondioxide on burning magnesium

When a piece of burning magnesium is lowered into a gas jar of carbon dioxide gas. It continues burning for a short time wth spluttering flame forming black particle and white arsh of magnesium oxide.

Explanation

Magnesium burns liberating a lot of heat energy which decomposes carbon dioxide to carbon and oxygen.

The oxygen liberated supports continous burining of magnesium

Therefore overall question is got by combining equations  (i) and  (ii)

Effect of carbon dioxide on lime water (calcium hydroxide solution)

When carbondioxide is bubbled into lime water the solution turns milky due to formation of insoluble calcium carbonate.

With excess carbondioxide, the milk solution turns colourless due to formation of soluble calcium hydrogen carbonate.

If the resulting colourless solution is heated a white precipitate forms due to decomposing f soluble calcium hydrogen carbonate to give insoluble calcium carbonate.

Reaction with sodium hydroxide solution

Sodium hydroxide solution absorbs carbondioxide to form a colourless solution of sodium carbonate.

With excess carbondioxide gas, a white precipitate os slightly soluble sodium hydrogen carbonate is formed.

Equation

Anhydrous sodium carbonate is prepared by bubbling excess carbondioxide, free from acid, through moderately concentrated sodium hydroxide solution.

Initially the solution remained colourless because sodium carbonate first formed is soluble in water with excess carbondioxide, a white precipitate of slightly soluble sodium hydrogen carbonate is formed.

The white precipitate is filtered off and washed with hot water and is heated to constant mass.

Anhydrous sodium carbonate is a white powder referred to as soda ash. It is used in glass manufacture, soap preparation, sodium hydroxide and for softening water

Uses of carbondioxide gas

1. Used in fre extinguishes to put out fires.

Properties that make it a good fire extinguisher

“doesn’t support burning  (combustion)”.

2. It is used to give a pleasant taste for soft drinks e.g beers, water and soda.
3. Used as a good refrigerant

Property

1. It sublimes
2. Its colder than ice
3. Used in the manufacture of sodium hydrogen carbonat by salvary process.
4. Making rain; pieces of solid carbondioxide (dry ice) are sometimes dropped in clouds to coll them enough to make it rain.

Cu

Ammonium carbonate is also soluble in water

 Effect of heat on carbonates

Carbonates of sodium and potassium are not affected by heating (do not decompose.) carbonates of calcium, magnesium, zinc, irom, lead ad copper decompose on heating to give the oxide of metal and a colourleess gas that turns blue litmus faint pink ad lime water milky. (carbondioxide)

 Lead (II) carbonate

It is a white powder, it decomposes on strong heating to give a colorless gas which turns blue litmus faint and lime water milky.

The residue is reddish- brown (orange when hot and yellow on cooling (lead (II) oxide).

Zinc carbonate

• White powder. On heating, white powder turns yellow when hot and back to white when cooling. (Zinc (II) oxide).
• Colourless gas is given off which turns blue litmus faint pink and lime waeter milky. (carbondioxide) colourless liquid which turned anyhydorus copper (II) sulpahet blue water

Copper (II) nitrate

• Green powder

On strong heating, green powder turns black (copper (II) oxide)

Colourless gas which turns lime water milky (carbondioxide)

• Colourless liquid which turns anhydrous copper (II) sulphate blue waer.

 Calcium carbonate, CaCO3

White soli. On heating there is no colour change. This is because the carbonate and  oxide are white. Colourless gas is given off which turns blue litmus faint pink and lime water milky.

 Preparation of some carbonates

Copper (II) carbonate –

It  is prepared by reacting copper (II) sulpahte solution which turns sodium carbonate solution.

A green precipitate is formed which is filtered, washed and dries.

 Note;

In the reaction, bsic copper (II) carbonate is formed. CuCO3.Cu (OH) ₂ (s)

Calcium crbonte; prepared by bubbling lead (II) nitrate solution with sodium hydrogen carbonate solution. A white precipitate of lead carbonate is formed.

The white precipitate is filtered off, washed with hot distilled water and dries.

If sodium carbonate solution is used basic lead carbonate is formed

Ammonium carbonate

It is prepared as a sublimate by heating ammonium sulphate with calcium carbonate.

The reaction is double decomposition / double displacement.

Ammonium carbonate is used as a constituent of smelling salts because it decomposes readily to give ammonia which stimulates reaching.

 Preparation of sodium carbonates

It’s prepared by passing carbondioxide gas (free form hydrochloric acid) into moderately concentrated sodium hydroxide solution for some time until finally a white precipitate of sodium hydrogen carbonate appears.

 With excess CO₂ (g)

The white precipitate is filtered ff and washed with cold distilled water.

Anhydrous sodium carbonate is obtained (soda ash) by heating the washed precipitate to constant mass.

Colourless (transparent) crystals of sodium carbonate, ten water, Na₂CO₃.10H₂O (l) are obtained by dissolving anhydrous sodium carbonate in the minimum volum of hot ware and cooling the solution to obtain the transparent crystals.

Na₂CO₃·10H₂O – washing soda

Uses of washing soda (read)

Properties of washing soad

It consists of large translucent crystals

On exposure to air, the crystals reduce mass and become coated with a fne white powder render then opaque.

Explanation; on exposure to air, Na₂CO₃·10H₂O lose water of crystallization

Efflorescence

Representative equation

Na₂CO₃·10H₂O

Anhydrous sodium carbonate can be obtained by heating hydrated sodium carbonate.

Aqueous sodium carbonate is alkaline due to hydrolysis

Salts of weak alkalines and strong bases are alkaline in aqueous solution

Manufacture of sodium carbonate by strong process – (ammonia – soda process)

Brine (concentrated sodium chloride solution) is saturated with ammonia and then carbondioxide. Carbondioxide reacts with ammonia solution to give ammonium hydrogen carbonate.

A VIDEO ABOUT EFFLORESCENCE

Ammonium hydrogen carbonates in turn rects with sodium chloride to form sodium hydrogen carbonate and ammonium chloride.

Less soluble sodium hydrogen carbonate is precipitated; the white precipitate is filtered off and is heated to constant mass.

Carbon dioxide from this decomposition is recycled along with some obtained from thermal decomposition of lime stone

The calcium oxide is warmed with ammonium chloride to regenerate the ammonium for further use.

Anhydrous sodium carbonate produced above is a white powder. Crystallization form aqueous solution gives the decahydrate, Na₂CO₃·10H₂O (washing soap)

Uses of sodium hydrogen carbonate

1. Used in fire extinguishers and in baking powder

• Sodium hydrogen carbonate in stomach powder neutralizes excess acids thus reliving indigestion.
• Sodium hydrogen carbonate is baking soda

Reaction of sodium carbonate solutions with metal cations

Like sodium hydroxide, sodium carbonate solutions forms precipitate with some metal cations