Carbon And Its Compounds

(a) –CHO

(b) or –C=O

The electronic dot structure of CO₂ is shown below.

Carbon has the ability of bond with other atoms of carbons forming large chains, branches or rings. This property is called catenation.

Also, carbon has a valency of four and can combine with other elements such as hydrogen, oxygen, nitrogen, etc. Due to its small size, the bonds formed by carbon with other elements are very strong. Hence, carbon forms a wide variety of compounds.

The size of silicon atom is larger than that of carbon atom causing a reduced force of attraction between electrons and the nucleus. In other words, the compounds formed by silicon are very reactive whereas the compounds formed by the carbon are very stable. That is why silicon does not exhibit the property similar to carbon.

Ester is the product obtained from esterification reaction. These compounds are responsible for the pleasant smell of fruits. It is found in fruits such as apples, mangoes, pineapples, strawberries etc. Sometimes, esters are used as flavouring agents in food items and in perfumes as well.

In industries, hydrogenation is used to reduce vegetable oils to vanaspati ghee. Vanaspati ghee is used as a substitute for ghee or butter containing animal fats which are harmful to our health and is cheaper than butter. Vegetable oils are unsaturated and they are hydrogenated in the presence of catalysts like nickel or palladium. The chemical reaction can be represented by the equation:

(a) IUPAC name: Methyl methanoate

(b) IUPAC name: Methanal

Ethanol undergoes oxidation to yield ethanoic acid. This oxidation is done with the help of strong oxidizing agents like alkaline potassium permanganate (KMnO₄) and acidified potassium dichromate (K₂Cr₂O₇) in the presence of heat.

Concentrated sulphuric acid can act as a dehydrating agent. Hence, ethanol when heated at 443 K with excess conc. H₂SO₄ undergoes dehydration reaction to form ethene.

The reaction involved is,

Esterification is the process of producing an ester from the reaction of an alcohol and a carboxylic acid. An acid is used as the catalyst. The general reaction can be expressed as:

The –OH part of alcohol and the –H present in acid get removed and form water as the byproduct. The nomenclature of ester is of the form “alkyl alkanoate” where the alkyl part is derived from the alcohol and the alkanoate part is derived from the carboxylic acid.

Saponification is considered the reverse reaction of esterification. Esterification is the process of producing esters by the reaction of an alcohol and a carboxylic acid. Saponification is the process in which an ester upon hydrolysis in the presence of a base gives back the alcohol and the carboxylic acid.

This process is called saponification because this is used in the preparation of soap. Soaps are sodium or potassium salts of long chain carboxylic acids.

Addition reactions are reactions in which two or more molecules combine to form a larger molecule, with no other products. No atoms or molecules get eliminated in this reaction. An example of addition reaction is the hydrogenation of alkenes to form alkanes.

Unsaturated compounds i.e., compounds containing double or triple bond(s) undergo addition reactions very easily. To accommodate the new incoming atom(s) (in the case of hydrogenation, the incoming atom is hydrogen), the double/triple bond(s) gets cleaved and converted into single bonds such that all elements present in the compound get a stable electronic configuration.

A series of compounds in which the same functional group substitutes for hydrogen in a carbon chain is called homologous series.

Consider the homologous series of alcohols – methanol, ethanol, etc. Note that methanol (CH₃OH) is obtained by replacing one of the H atoms with –OH group. Similarly, the –OH group replaces one of the H atoms of ethane (CH₃CH₃) to form ethanol
(CH₃CH₂OH) and so on. The chemical properties of these compounds are similar. The successive members of the homologous series differ by a –CH₂ unit.

For example, CH₃OH and CH₃CH₂OH, CH₃CH₂OH and CH₃CH₂CH₂OH differ by a –CH₂ unit.

Also, members of a homologous series can be represented using a general formula. In the case of alcohols, the general formula is C_nH_2n+1O, where ‘n’ is the number of carbon atoms.

Scum is an insoluble precipitate formed due to the reaction of soap with calcium and magnesium salts present in hard water. As a result, soap does not form lather in hard water, making its cleansing action less effective in hard water.

Soaps are sodium or potassium salts of long chain carboxylic acids. They contain two ends having different properties: the carboxylic acid part which is hydrophobic and the ionic end (Na⁺ or K⁺) which is hydrophilic.

Structure of a soap molecule

Dirt present in clothes is basically a hydrocarbon. When soap is used in water, the soap molecules tend to surround the dirt such that they form a cluster in which the hydrophobic tails are in the interior of the cluster and the hydrophilic part are on the surface of the cluster (see figure below). The hydrophilic part dissolves in water and the hydrophobic part dissolves in the hydrocarbon (dirt). This formation or cluster is called micelle.

Formation of micelle

Agitating the water by hand or brush forces the hydrophilic end to move along the direction of agitation of water, dragging the micelle holding the dirt out of the clothes and the dirt is rinsed away. In short, the cleansing action of soap is achieved by the formation of micelles.

The compound is ethanoic acid also known as acetic acid (CH₃COOH). It is a weak organic acid. CH₃COOH reacts with carbonates and bicarbonates to release CO₂ which is a colourless gas. The reactions involved are:

2CH₃COOH + Na₂CO₃→ 2CH₃COONa + CO₂↑ + H₂O

CH₃COOH + NaHCO₃→ CH₃COONa + CO₂↑ + H₂O

Alcohols can be distinguished from carboxylic acid using the sodium carbonate (Na₂CO₃) or sodium bicarbonate (NaHCO₃) test. Alcohols do not react with sodium carbonate or bicarbonate, whereas acid reacts with them to release carbon dioxide.

2RCOOH + Na₂CO₃→ 2RCOONa + CO₂↑ + H₂O

RCOOH + NaHCO₃→ RCOONa + CO₂↑ + H₂O

Alcohol + Na₂CO₃→ No reaction

Physical Properties:

Both Ethanol and ethanoic acid are liquids at room temperature and have distinct melting and boiling points.

Chemical Properties:

Ethanoic acid produces CO₂ when reacted with carbonates or bicarbonates. Ethanol does not react with carbonates or bicarbonates.

Ethanoic acid reacts with a base (say NaOH) to give salt and water:

CH₃COOH + NaOH → CH₃COONa + H₂O

Ethanol reacts very slightly with NaOH.

Butter is basically made of animal fats which contain saturated fatty acids. Cooking oil on the other hand, contains long unsaturated fatty acids. This means that vegetable oils can be hydrogenated whereas butter cannot be hydrogenated.

A reaction in which one atom or a group of atoms is replaced by another atom or another group of atoms is called substitution reaction. For example, consider the photochemical reaction of methane with chlorine. In the presence of sunlight, one of the H atoms is replaced by Cl atom. Gradually, each H gets replaced by Cl. The reaction can be represented by the equation:

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

CH₃Cl + Cl₂→ CH₂Cl₂ + HCl and so on.

(i) When a mixture of air and ethyne (C₂H₂) is used, incomplete combustion takes place and as a result a sooty flame is obtained, which is not effective for welding.

If ethyne is burned with oxygen, complete combustion takes place and gives a clean flame which is ideal for welding. This welding is also known as oxy-acetylene welding.

(ii) Carbon has 4 valence electrons. The two given situations can be analysed separately.

To form C⁴⁺ cation, it has to lose 4 electrons, but an enormous amount of energy is required to remove the electrons, because of the strong nuclear force of attraction.

To form C^4- anion, it has to gain 4 electrons, but it would be difficult for the nucleus with 6 protons to hold onto 10 electrons. In brief, the anion formed would not be stable.

9 structural isomers can be drawn for isoheptane (C₇H₁₆). They are listed below along with their structural formula.

1. 2-methyl hexane (isoheptane)

2. n-heptane

3. 3-methyl hexane

4. 2,2-dimethyl pentane

5. 2,3-dimethyl pentane

6. 2,4-dimethyl pentane

7. 3,3-dimethyl pentane

8. 2,2,3-trimethyl butane

9. 3-ethyl pentane

The formula of cyclohexane is C₆H₁₂. The structure is shown below:

Electron dot structure of cyclohexane

Even though diamond and graphite are made up of carbon atoms only, the molecular structure of diamond is different from that of graphite. Diamond has a 3D structure, whereas the structure of graphite consists of layers of carbon stacked above one another.

The structural formula of ethane is

Note that there are 6 C-H bonds and 1 C-C bond.

Names of carbon compounds ending in ‘–one’ have ketone (-C=O) as the functional group.

The bottom of the vessel is blackened due to the incomplete combustion of the fuel. Hence, one can say the fuel is not burning properly.

One of the H atoms of alkanes (having the molecular formula C_nH_2n+2) is replaced by an –OH group to form alcohols.

Thus C_nH_2n+2 – (1 H) + (1 –OH) → C_nH_2n+1—OH

Oxidation of ethanol using alkaline KMnO₄ or acidified K₂Cr₂O₇ gives ethanoic acid.

Alkynes are carbon compounds containing one or more C≡C bonds. One can generalize the formula from the examples C₂H₂, C₃H₄ etc.

One bond is formed by sharing 2 electrons, and therefore a triple bond is formed by 6 electrons or 3 pairs of electrons.

The effervescence is due to the formation of CO₂ when NaHCO₃ is treated with carboxylic acids.

RCOOH + NaHCO₃→ RCOONa + CO₂↑ + H₂O

Nitrogen atoms share 3 pairs of electrons to form a triple bond (N≡N) to attain stable electronic configuration.

Ethyne is the alkyne consisting of 2 carbons with a triple bond between them.

Chlorine reacts rapidly with saturated hydrocarbons in the presence of sunlight. One such reaction is,

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

Carbon atom has 2 electrons in its innermost shell and 4 valence electrons. When it forms covalent bonds with 4 univalent atoms, it gets an additional 4 electrons as a result of sharing them. Now there are 8 electrons in its outermost shell. This resembles the electronic configuration of neon, which has the electronic configuration 2, 8.

Oxygen forms single covalent bonds with hydrogen. Having 6 valence electrons, 2 of them contribute to the covalent bond. After bond formation oxygen would have 2 shared pairs of electrons and 2 lone pairs of electrons.

Mark the longest chain of the given compound. If no carbon atoms are remaining after marking the chain, then the compound is not branched. If one or more carbon atoms are not marked in the longest chain, then they are said to be branches.

Unsaturated hydrocarbons are compounds of carbon and hydrogen which contain double bonds and/or triple bonds.

There are 4 C-C bonds and 12 C-H bonds.

Na + CH₃CH₂OH → CH₃CH₂ONa + H₂

5%–8% acetic acid in water

The other three compounds form a homologous series of alkanes (C_nH_2n+2), whereas C₄H₈ is an alkene (C_nH_2n).

The compound contains 3 carbons. The alkane with 3 carbons is “propane”. There is a –CHO group (aldehyde) in this compound. Hence the name would contain the suffix “-al”.

The IUPAC name would then be:

Propane – ‘e’ + ‘-al’ → Propanal

Heteroatoms are the elements which replace hydrogen in a hydrocarbon. In the given compound, H is replaced by oxygen and chlorine.

Alkynes are carbon compounds containing one or more triple bonds. The lowest member (or the first member) is formed by 2 carbon atoms, which is ethyne.

True

False

Alcohols react with sodium to evolve hydrogen gas, along with the formation of sodium alkoxides.

Alcohol + Na → Sodium alkoxide + H₂

True

False

Esters are formed as a result of reaction between an alcohol and a carboxylic acid.

True

False

Carbon in its allotropic forms under suitable conditions, burns in oxygen to produce carbon monoxide or carbon dioxide depending on the extent of combustion. Incomplete combustion results in the evolution of carbon monoxide, whereas complete combustion would result in the formation of carbon dioxide.

True

False

Animal fats contain saturated fatty acids which are harmful for our health. Vegetable oils on the other hand, contain unsaturated fatty acids which are good for our health.

False

Nitrogen molecule is formed by the sharing of 3 pairs of electrons.

The electron dot structure of N₂ is shown:

True