Chapter 4 Carbon and Its Compound

Structural representation of electron in CO2

Sulphur molecule exists as S₈. Its dot structure is

Three structural isomers are possible for pentane.

(i) Pentane

CH₃ - CH₂ - CH₂ - CH₂ - CH₃

(ii) 2 Methyl butane (Isopentane)

(iii) 2,2,dimethyl propane (Neopentane)

The two main features of carbon that give rise to a large number of compounds are as follows:

(i) Catenation − It is the ability to form bonds with other atoms of carbon.

(ii) Tetravalency − Carbon has four valence electrons, carbon is capable of bonding with four other atoms.

Cyclopentane is C₅H₁₀. Its electron dot structure is:

(i) Ethanoic acid

(ii) The structural isomers possible for bromopentane. Among them, the structures of three isomers are:

(i) Bromoethane

(ii) Methanal (formaldehyde)

(iii) Hexyne

The conversion of ethanol to ethanoic acid involves the addition of oxygen to ethanol, hence it is an oxidation reaction.

Because when ethyne is burnt in air, it gives a sooty flame. This is due to incomplete combustion caused by limited supply of oxygen. However, if ethyne is burnt with oxygen, it gives a clean flame with temperature 3000°C because of complete combustion. This oxy-acetylene flame is used for welding. It is not possible to attain such a high temperature without providing oxygen. This is the reason that a mixture of ethyne and air is not used.

We can experimentally distinguish between an alcohol and a carboxylic acid by reacting with carbonates and hydrogen carbonates. Acid reacts with carbonate and hydrogen carbonate to evolve CO₂ gas that turns lime water milky.

Metal Carbonate/Metal Hydrogncarbonate + Carboxylic acid
                                             ↓                    
                          Salt + Water + Carbon dioxide

Alcohols, on the other hand, do not react with carbonates and hydrogen carbonates.

Those chemical compounds which have capability of adding oxygen to other reactant substances. Some substances such as alkaline potassium permanganate and acidified potassium dichromate are capable of adding oxygen to others. These are known as oxidising agents.

Detergents are ammonium or sulphonate salts of long chain carboxylic acids. Unlike soap, they do not react with calcium and magnesium ions present in hard water to form scum. Detergent produces a good amount of lather irrespective of whether the water is hard or soft. This means that detergents can be used in both soft and hard water. Therefore, it cannot be used to check whether the water is hard or not.

A soap molecule has two parts: hydrophobic head and hydrophilic tail. With the help of these, it attaches to the grease or dirt particle with the hydrophobic end of the soap molecule and forms a cluster around dirt called micelles. These micelles remain suspended as a colloid. To break these micelles (entrapping the dirt), it is necessary to agitate clothes.

(b) There are 7 covalent bonds in ethane.

(c) The functional group of butanone is ketone.

(b) While cooking, if the bottom of the vessel is getting blackened on the outside, the fuel is not burning completely.

Carbon can neither lose four of its electrons nor gain four electrons as both the processes require an extra amount of energy and that would make the carbon atom unstable. Therefore, it completes its octet by sharing its four valence electrons with other carbon atoms or with atoms of other elements. The bonds that are formed by sharing electrons are known as covalent bonds. In covalent bonding, both the atoms share the valence electrons.

(a) Ethanoic acid

(b) H₂S

(c) Propanone

(d) F₂

A homologous series is a series of carbon compounds that have different numbers of carbon atoms but contain the same functional group.

For example, methane, ethane, propane, butane, etc. are all part of the alkane homologous series. The general formula of this series is C_nH_2n+2.

Methane - CH₄

Ethane - CH₃CH₃

Propane - CH₃CH₂CH₃

Butane - CH₃­CH₂CH₂CH₃

In a homologous series of alkane there is a difference of one carbon and 2 hydrogen unit between each successive member.

A soap is a sodium or potassium salt of long chain carboxylic acids. It has one polar end and one non-polar end. The polar end is hydrophilic in nature which is attracted towards water. The non-polar end is hydrophobic but lipophilic, i.e., it is attracted towards hydrocarbons. When soap is added to water, soap molecules arrange themselves in a cluster, the non-polar portion out of water such that the non-polar ends are in the interior of the cluster attached with dirt and the polar ends are on the surface of the cluster. Since the dirt present on clothes is oily in nature and insoluble in water, the hydrophobic ends of the clusters attach themselves to the dirt. This cluster of soap molecule formation in which the dirt is entrapped is called micelles.

Micelle formation does not occur in alcohol because the alkyl chain of soap becomes soluble in alcohol.

Carbon compounds give a lot of heat and light when burnt in air. Saturated hydrocarbons burn with a clean flame and no smoke is produced. The carbon compounds, used as a fuel, have high calorific values. Therefore, carbon and its compounds are used as fuels because they for most applications.

Soap does not work properly in hard water. A soap is a sodium or potassium salt of long chain carboxylic acid. Hard water contains salts of calcium and magnesium. When soap is added to hard water, sodium and potassium ions present in soap displace calcium or magnesium ions from the water molecules forming an insoluble substance called scum. A lot of soap is wasted in the process.

For example:

Sodium Stearate + Calcium chloride → Sodium chloride + Calcium Stearate (scum)

Formation of scum hinders the formation of foam, so soap is thus unable to clean in hard water.

Since soap is basic in nature, it will turn red litmus blue. However, the colour of blue litmus will remain blue, because soap is sodium salt of fatty acid. It is obtained by treatment of oil with caustic soda. Sodium stearate is thus a salt of weak acid and strong base, so it is alkaline in nature.

Hydrogenation is the process of addition of hydrogen to unsaturated hydrocarbons in the presence of palladium and nickel catalysts to give saturated hydrocarbons.

Unsaturated hydrocarbons undergo addition reactions. As these are unsaturated hydrocarbons, C₃H₆ and C₂H₂ undergo addition reactions.

• Butter contains saturated fats. Therefore, it cannot be hydrogenated. On the other hand, oil has unsaturated fats. That is why it can be hydrogenated to saturated fats (solids).
• Bromine water test - Cooking oil will decolourise the red colour of bromine water on shaking while butter will not.

The dirt present on clothes is oily in nature and insoluble in water. Therefore, it cannot be removed by only washing with water. When soap is dissolved in water, its hydrophobic ends attach themselves to the dirt and remove it from the cloth. Then, the molecules of soap arrange themselves in micelle formation and trap the dirt at the centre of the cluster. These micelles remain suspended in the water. When flushed with excess water, the dust particles are easily rinsed away by water.