Carbon and its Compounds Class 10 – Continuing our series for Class 10 Revision for CBSE board exams, we bring you a new chapter today i.e. Carbon and its Compounds Class 10. Looking at previous years’ questions, we suggest that it is a very very important chapter from exam point of view and is asked for at least 6-7 marks every year, so you read this thoroughly. Every year, at least 2 to 3 theory and practical questions are asked from this chapter.
The concepts that are going to be discussed in this article are:
- Covalent bonding in carbon compounds
- Versatile nature of carbon
- Allotropes of carbon
- Saturated and unsaturated carbon compounds
- Chains, branches and rings in carbon compounds and Isomers
- Functional groups
- Homologous series
- Nomenclature of carbon compounds
- Chemical properties of carbon compounds
- Properties of ethanol and ethanoic acid
- Soaps and detergents
- Previous Years’ question
Let’s discuss each topic of Carbon and its Compounds Class 10 one-by-one
Covalent bonding in carbon compounds:
Carbon has 4 electrons in its outermost shell. carbon tries to achieve a stable configuration by sharing electrons, rather than giving or taking them. The bond formed by sharing of electrons is called covalent bond. It can be seen in some compounds other than carbon also, like H2:
Versatile Nature of Carbon
Carbon forms a great number of compounds. The number of carbon compounds known to chemists are estimated at around 3 million! Carbon is able do so because of its following properties:
- Catenation – The ability of carbon to form bonds with other atoms of carbon is termed catenation. This gives rise to long chain carbon compounds.
- Tetra-valency – Since carbon has a valency of four, it can form 4 bonds. Compounds of carbon are seen with oxygen, hydrogen, nitrogen, sulfur, chlorine and many other elements. The compounds of carbon containing only carbon and hydrogen are called hydrocarbons.
Allotropes of Carbon
We saw that carbon can form bonds with carbon. The way in which carbon atoms combine with each other can be different, giving rise to compounds with different properties. Such different forms of the same element are called allotropes. Allotropes of carbon include graphite, diamond, C-60 or buckminsterfullerene.
You can now see on your board some common properties of these 3 allotropes of carbon.
Saturated and Unsaturated Hydrocarbons
Unsaturated hydrocarbons are hydrocarbons that have double or triple covalent bond(s) between adjacent carbon atoms. Saturated hydrocarbons, on the other hand, contain only single bond in them.
- The hydrocarbons containing only carbon carbon single bonds are called alkanes.
- The hydrocarbons containing carbon carbon double bond(s) are called alkenes.
- The hydrocarbons containing carbon carbon triple bond(s) are called alkynes.
Chains, Branches and Rings in Carbon Compounds & Isomers
We see that carbon compounds can either contain a straight chain, branches, or can be in the form of a ring.
For example, consider C4H10 or butane. We can satisfy the formula by making the structure in 2 different ways:
Such compounds with identical molecular formula but different structures are called structural isomers.
We have seen that carbon forms bonds with a number of different elements like halogen, sulphur, nitrogen, oxygen, etc. In a hydrocarbon chain, one or more hydrogens can be replaced by these elements, such that the valency of carbon remains satisfied.
Depending upon the element or group of elements that form bonds with carbon, the properties of the compound changes. Such an element or group of elements is called a functional group. Some common functional groups and their names are given below:
To understand the concept of homologous series, let us take the example of methanol. We know that to make methanol or CH3OH, we remove a hydrogen atom from CH4, and add an -OH group in its place. Similarly, to make other alcohols, we need to keep removing one -H from higher hydrocarbons and add an -OH. However, we can also say, that we are simply adding ‘CH2’ units to methanol. Adding one unit of CH2 will give us ethanol. Adding 2 will give us propanol, and so on.
Such a series of alcohols that we get on repeatedly adding CH2, have been observed to possess similar properties.
Similarly, we can create a series of aldehydes, ketones, carboxylic acids, etc, where each compound differs from the previous by ‘CH2’. Such series are called homologous series. Members of a homologous series have similar properties, and can all be represented by a general formula. Here are some examples of general formulae –
Alcohols – CnH2n+1OH
Alkanes – CnH2n+2
Alkenes – CnH2n
Alkynes – CnH2n-2
You can see that we can form this series of alcohols as :
CH3OH, C2H5OH, C3H7OH, … these can be represented by general formula, CnH2n+1OH.
Similarly, you see that the series of alkanes like CH4, C2H6, C3H8, etc, differ by a -CH2 unit, and can be represented by general formula CnH2n+2
Similarly, general formula for alkenes is CnH2n
And that of alkynes is CnH2n-2
Such a series of compounds possessing similar properties and having a general formula is called a homologous series.
Nomenclature of carbon and its compounds
- Based on number of C atoms: Suffix ‘-ane’ is used when only single bonds are present in the carbon compound.
|Number of C atoms||Compound||Name|
- Based presence of double or triple bond: Suffix ‘-ene’ or ‘-yne’ is used, depending on the presence of double or triple bond(s) respectively.
- Based on Functional Group:
|Functional group||Prefix / suffix||Name|
|Halogen||Prefix-chloro, bromo, etc||Chloropropane, Bromopropane|
|Alcohol||Suffix – ol||Propanol|
|Aldehyde||Suffix – al||Propanal|
|Ketone||Suffix – one||Propanone|
|Carboxylic acid||Suffix – oic acid||Propanoic acid|
Chemical Properties of Carbon Compounds
- Combustion – Carbon compounds burn in the presence of oxygen to give carbon dioxide along with release of heat and light. Eg. C+O2→CO2+heat and light
- Oxidation – refers to addition of oxygen. Eg.
- Addition – Unsaturated hydrocarbons add hydrogen in the presence of catalysts such as palladium or nickel to give saturated hydrocarbons. This reaction is commonly used in the hydrogenation of vegetable oils. Eg.
- Substitution – when one type of atom or a group of atoms takes the place of another, it is called a substitution reaction. For eg, in the presence of sunlight, chlorine is added to hydrocarbons and replaces the hydrogen atoms one by one. CH4+Cl2→CH3Cl+HCl (in the presence of sunlight)
Properties of Ethanol and Ethanoic Acid
Properties of ethanol and ethanoic acid – properties, uses and some reactions of ethanol and ethanoic acid have been dealt with in this chapter, which we will now see.
- Formula: CH3CH2OH
- Second member of the homologous series of alcohols (first member is methanol or CH3OH)
- Ethanol is a colourless liquid at room temperature having a pleasant smell and a burning taste.
- It has a low boiling point (78℃ or 351 K).
- It mixes with water in all proportions.
- It is a covalent and neutral compound.
- Ethanol is commonly called alcohol or ethyl alcohol.
Uses of Ethanol:
- Ethanol is used in the manufacture of paints, medicines, perfumes, dyes, soaps, etc.
- It is used as a solvent. Many organic compounds that are insoluble in water, are soluble in ethanol.
- Being a good solvent, ethanol is used in medicines such as tincture iodine, cough syrups and many tonics.
- It is also used as a fuel in cars along-with petrol.
- It is used in all alcoholic drinks.
- It is used as an antiseptic to sterilize wounds and syringes in hospitals.
Reaction of Ethanol with sodium:
- Formula: CH3COOH
- Common name: Acetic Acid
- Second member of the homologous series of carboxylic acids (first member is methanoic acid or CH3OH)
- A 5−8% dilute solution of ethanoic acid in water is called vinegar and is used as a preservative in pickles.
- Ethanoic acid has a very high freezing point (16℃). It often freezes in winters to form a colourless, ice-like solid. Hence, it is often called glacial acetic acid or glacial ethanoic acid.
Uses of Ethanoic Acid:
- A dilute solution of ethanoic acid (vinegar) is used as a preservative in pickles and ketchup.
- Ethanoic acid is used for making esters, which are used in perfumes and as flavoring agents.
- Ethanoic acid is also used for making a lot of other organic compounds.
Reactions of Carbon and its Compounds
- Esterification: Esters are sweet-smelling substances. These are used in making perfumes and as flavouring agents. Esters react in the presence of an acid or a base to give back the alcohol and carboxylic acid. This reaction is known as saponification because it is used in the preparation of soap
- Reactions with a base: 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
Soaps and Detergents
Presence of calcium or magnesium ions in water can make it hard. When soap is added to hard water, a white substance called scum is formed, which makes cleaning of clothes difficult. This is because when soap molecules react with calcium or magnesium ions, they form an insoluble white precipitate.
Thus, soap is rendered useless in hard water. Thus, detergents are used. Detergents are ammonium or sulphonate salts or long chain carboxylic acid derivative, which on reaction with calcium or magnesium ions do not form scum and help in efficient cleaning.