Chapter 4. Carbon and its Compounds

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Combustion: Combustion is the burning of compounds in air to give CO₂ and water. 

(i) Combustion of Methane (CH₄) in air the reaction is as follows:

CH₄ + 2O₂ → CO₂ + 2H₂O + heat and light

(ii) Combustion of Ethanol (CH₃CH₂OH) in air gives CO₂ water, heat and light. 

CH₃CH₂OH + 3O₂ → 2CO₂ + 3H₂O + heat and light.

Above example you have seen that how carbon compounds release heat and light on burning. 

Carbon Compound As Fuels: 

The most carbon compounds release a large amount of heat and light on burning. 

Oxidation: Oxidation is a reaction in which carbon compounds take up oxygen in the presence of oxidising agents to form another carbon compound. 

Oxidising Agent: some substances are capable of adding oxygen to others.
These substances are known as oxidising agents. Example: Alkaline potassium permanganate and acidified potassium dichromate are oxidising agent. 

Oxidation of ethyle Alcohol by Alkaline potassium permanganate or acidified potassium dichromate: 

When some drops of alkaline potassium permanganate o acidified potassium dichromate is added with heated ethyle alcohol it get oxidised and a complete oxidation takes place and it forms acetic acid. 

The equation of this reaction is as follows:

Addition Reaction: An atom or group of atoms are added to an unsaturated compound. 

"The reaction in which adds the substances is known as Addition reaction."

This reaction is commonly used in the hydrogenation of vegetable oils using a nickel catalyst. 

Catalysts: Catalysts are substances that cause a reaction to occur or proceed at a different rate without the reaction itself being affected.

Unsaturated hydrocarbons add hydrogen in the presence of catalysts
such as palladium or nickel to give saturated hydrocarbons.

For Example: 

Hydrogenation Reaction:

Unsaturated hydrocarbons add hydrogen in the presence of catalysts such as palladium or nickel to give saturated hydrocarbons is called hydrogenation. This reaction is commonly used in the hydrogenation of vegetable oils using a nickel catalyst in industry.

Vegetable oils generally have long unsaturated carbon chains while animal fats have saturated carbon chains.

Which is better, and Why? 

Unsatuared fatty acids (vegetable oils) are ‘healthy’. Animal fats generally contain saturated fatty acids which are said to be harmful for health. Oils containing unsaturated fatty acids should be chosen for cooking.

Substitution Reaction: An atom or group of atom or a group present in a saturated compound is replaced by another atom or group. 

Chlorine is a hetroatom which removes hydrogen from carbon compound. 

Example of substitution reaction: 

When chlorine is added to hydrocarbons in the presence of sunlight It replaces hydrogen atoms one by one. This is very fast reaction. Chlorine forms functional group of halogen. 

Example: When chlorine (Cl₂) is added to Methane (CH₄), this reaction gives chloro-methane and hydrochloric acid. [Here substitution of hydrogen is taken place by chlorine] 

CH₄ + Cl₂ → CH₃Cl + HCl (in the presence of sunlight)

Chemical properties of carbon compounds:

Chemical properties of carbon compounds are followings;

(i) Carbon, in all its allotropic forms, burns in oxygen to give carbon dioxide along with the release of heat and light.

(ii) Most carbon compounds also release a large amount of heat and light on burning.

(iii) Carbon compounds can be easily oxidised on combustion.

(iv) Unsaturated hydrocarbons add hydrogen in the presence of catalysts such as palladium or nickel to give saturated hydrocarbons.

(v) Saturated hydrocarbons are fairly unreactive and are inert in the presence
of most reagents.

Features of saturated and unsaturated hydrocarbons on burning: 

• Saturated hydrocarbons generally gives a clean flame while
  unsaturated carbon compounds gives a yellow flame with lots of
  black smoke.

Causes of giving sooty flame by saturated hydrocarbons: 

Due to the limit  supply of air results in incomplete combustion of even saturated hydrocarbons giving a sooty flame. The gas/kerosene stove used at home has inlets for air so that a sufficiently oxygen-rich mixture is burnt to give a clean blue flame.

The bottoms of cooking vessels getting blackened it means that

(i) The air holes are blocked

(ii) fuel is getting wasted.

Disadvantages of burning fuels such as coal and petroleum: 

(i) The combustion of coal and petroleum results in the formation of oxides of sulphur and nitrogen which are major pollutants in the environment.

(ii) Incomplete combustion of coal and petroleum gives a sooty flame.

(iii)  Incomplete combustion of coal and petroleum also gives carbon Monooxides which is dangerous poluutant. 

Incomplete combustion of coal and petrolium: 

(i) Incomplete combustion of coal and petroleum gives a sooty flame.

(ii)  Incomplete combustion of coal and petroleum also gives carbon Monooxides which is dangerous poluutant. 

Cause of some fuels burning without a flame: 

The coal or charcoal in an ‘angithi’ sometimes just glows red and gives out heat without a flame. This is because a flame is only produced when gaseous substances burn. When wood or charcoal is ignited, the volatile substances present vapourise and burn with a flame in the beginning.

Why some substances burns with luminous flame:

A luminous flame is seen when the atoms of the gaseous substance are heated and start to glow. The colour produced by each element is a characteristic property of that element.

Formation of coal and petroleum:

Coal and petroleum have been formed from biomass which has been subjected to various biological and geological processes. Coal is the remains of trees, ferns, and other plants that lived millions of years ago. These were crushed into the earth, perhaps by earthquakes or volcanic eruptions. They were pressed down by layers of earth and rock. They slowly decayed into coal. Oil and gas are the remains of millions of tiny plants and animals that lived in the sea. When they died, their bodies sank to the sea bed and were covered by silt. Bacteria attacked the dead remains, turning them into oil and gas under the high pressures they were being subjected to.

Alcohol: 

Ethanol (CH₃CH₂OH): 

Ethanol is commonly called alcohol. 

Physical Properties of Ethanol: 

(i) Ethanol is a liquid at room temperature.

(ii) It is a good solvent.

(iii) Ethanol is also soluble in water in all proportions.

(iv) It has highly flammability. 

Chemical properties of Ethanol: 

(i) Combustion: Ethanol burns in oxygen to produce carbon dioxide and water. 

(ii) Dehydration: Dehydration of ethanol is done by heating with concentrated sulfuric acid, which behave as a dehydrating agent. 

(iii) Oxidation: oxidation can be made by using oxidising agent like acidified potassium dichromate or alkaline potassium permanganate.  

(iv) Estrification: Ethanol can be reacted with carboxylic acid to form esters. 

Uses of Ethanol: 

(i) It is the active ingredient of all alcoholic drinks.

(ii) It is also used in medicines such as tincture iodine, cough syrups, and many tonics.

(iii) For synthesis of industrial methylated spirits.

(iv) Ethanol burns to give carbon dioxide and water and can be used as a fuel. 

Harmful effects of drinking Alcohols/Ethanol: 

(i) Consumption of small quantities of dilute ethanol causes drunkenness.

(ii) Short-term use of alcohol causes Slurred speech, drowsiness, vomiting and headache etc. 

(iii) Long-term consumption of alcohol leads to many health problems such as alcohol poisioning, liver disease, nerve damage and permanent damage of brain etc.

(iv) It tends to slow metabolic processes and to depress the central nervous system. This results in lack of coordination, mental confusion, drowsiness, lowering of the normal inhibitions, and finally stupour.

(v) The individual may feel relaxed but does not realise that his sense of judgement, sense of timing, and muscular coordination have been seriously impaired. 

(i) Reaction with Sodium:  Alcohols react with sodium leading to the evolution of hydrogen and the other product is sodium ethoxide.

The equation is as follows: 

2Na + 2CH₃CH₂OH → 2CH₃CH₂O–Na⁺ + H₂

                                           (sodium ethoxide) 

(ii) Reaction to give unsaturated hydrocarbon: Heating ethanol at 443 K with excess concentrated sulphuric acid results in the dehydration of ethanol to give ethene –

Denatured Alcohol: To prevent the misuse of ethanol produced for industrial use, it is made unfit for drinking by adding poisonous substances like methanol to it. Dyes are also added to colour the alcohol blue so that it can be identified easily. This is called denatured alcohol. 

Ethanoic Acid (CH₃COOH): 

Ethanoic acid is commonly called acetic acid and belongs to a group of acids called carboxylic acids.

• 5-8% solution of acetic acid in water is called vinegar and is used widely as a preservative in pickles.
• The melting point of pure ethanoic acid is 290 K (17 ^oC) and hence it often freezes during winter in cold climates. This gave rise to its name glacial acetic acid.

Properties: 

(i) It has acidic nature. 

(ii) Ethanoic acid is an odorless and highly smelling liquid.

(iii) Its melting point is 290 K. 

Use of Ethanoic Acid/Acetic Acid:

Group is called carboxylic Acid: 

The uses of ethanoic acid are followings: 

(i) It is used as preservative for preparing pickes in the form of vinegar.

(ii) It is used as laboratory's agent.

(iii) Manufacturing of white led.

(iv) It is used in the manufactering of Reyon fibres.   

(v) Acetic acid is used as coagulant in the manufacture of rubber.

(vi) It is used as a solvent.

Reactions of ethanoic acid:

(i) Esterification reaction: Esters are most commonly formed by reaction of an acid and an alcohol. Ethanoic acid reacts with absolute ethanol in the presence of an acid catalyst to give an ester –

The reaction is as;

Ester: The reaction by ethanol and ethanoic acid resulting forms the compound that is called Ester. The molecular formula of ester is CH₃COOCH₂CH₃.

Uses of Esters: 

Esters are sweet-smelling substances, the uses of esters are following.

(i) These are used in making perfumes and as flavouring agents.

(ii) These are also used to make surfactants such as soap and detergents.

(iii) Some esters can be made into polymers called polyesters. 

Esterification reaction: The reaction which gives Ester that is called estrification. 

Saponification: Ester reacts in the presence of an acid or a base to give back the alcohol and carboxylic acid this reaction is known as saponification.  

Because esters are used in preparation of soap. 

Equation for saponification reaction: 

(ii) Reaction with a base: Like mineral acids, ethanoic acid reacts with a base such as sodium hydroxide to give a salt (sodium ethanoate or commonly called sodium acetate) and water:

NaOH + CH₃COOH → CH₃COONa + H₂O

(iii) Reaction with carbonates and hydrogencarbonates: Ethanoic acid reacts with carbonates and hydrogencarbonates to give rise to a salt, carbon dioxide and water. The salt produced is commonly called
sodium acetate.
2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂
CH₃COOH + NaHCO₃ → CH₃COONa + H₂O + CO₂

 

Chapter 4. Carbon and It's Compounds

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Soap And Detergents: 

Soaps: The molecules of soap are sodium or potassium salts of long-chain carboxylic acids. The ionic-end of soap dissolves in water while the carbon chain dissolves in oil. The soap molecules, thus form structures called micelles.

Micelles : When soap is at the surface of water, inside water these molecules have a unique orientation that keeps the hydrocarbon portion out of the water. This is achieved by forming clusters of molecules in which the hydrophobic tails are in the interior of the cluster and the ionic ends are on the surface of the cluster. This formation is called a micelle.

               The Structure of Micelle

There are important roles of ends of soap molecules for formation of the structure of Micelle. 

The Micelle has two ends:

(i) Hydrophilic end: The end which dissolves in water is called hydrophilic end. 

(ii) Hydrophobic end: The end which dissolves in hydrocarbons (oily substances) is called hydrophobic end. 

Differences between hydrophilic end and hydrophobic end :

Hydrophilic end:

(i) It dissolves in water.

(ii) This is ionic end. 

(iii) The ionic ends are on the surface of the cluster.

Hydrophobic end:

(i) It dissolves in hydrocarbons.

(ii) This is not ionic end. 

(iii) The hydrophobic tails are in the interior of the cluster.

The cleaning process of soap: 

The cleaning process is characterised by soap micelle. The ionic end of soap is dissolves in water and other end dissolves in oily scum and thus forms structure of micelles. Thus micelles are able to clean as soap because oily scums gather in the center of micelles. There forms emulsion in the water. The micelles stay
in solution as a colloid and will not come together to precipitate because of ion-ion repulsion. Thus, the dirt suspended in the micelles is also easily removed away and our clothes are cleaned

Micelle properties:

(i) A micelle as soap is able to clean.

(ii) The micelles stay in solution as a colloid.

(iii) These are not precipitated due to ion-ion repulsion.

(iv) Soap micelle can disperse light.

(v) The micelles of soap help to dissolve oily scum in the water.

The soap does not form foam with hard water:

When we wash hand with soap in hard water, we see that foam formed with very difficulty and an insoluble substance (scum) remains after washing with
water. This is caused by the reaction of soap with the calcium and magnesium salts, which cause the hardness of water. Hence you need to use a larger amount of soap.

The detergent is more effective even in hard water: 

Detergents are generally ammonium or sulphonate salts of long chain carboxylic acids. The charged ends of these compounds do not form insoluble precipitates with the calcium and magnesium ions in hard water. Thus, they remain effective in hard water.

Differences between soap and detergent: 

Soap: 

(i) The molecules of soap are sodium or potassium salts of long-chain carboxylic acids.

(ii) It does not form foam in hard water. 

(iii) It increases the hardeness of water. 

(iv) It forms micelle during cleaning process. 

Detergent: 

(i) Detergents are generally ammonium or sulphonate salts of long chain carboxylic acids.

(ii) It form foam even in hard water. 

(iii) It increases the softness of water.

(iv) It does not form micelle during cleaning process.  

Use of detergents: 

(i) Detergents are usually used to make shampoos and products for cleaning clothes.