Carbon And Its Compounds

The bonding in which atoms mutually share the electron pair(s) to form molecules is called covalent bonding.

Example: Hydrogen molecule. In hydrogen molecule, both the electrons are shared to form a covalent bond.

Another very common example is the water molecule:

In water molecule, the two single hydrogen & oxygen bonds are formed.

The element X is oxygen. The atomic number is 8, and its electronic configuration is 2,6. Oxygen is used for respiration by the living beings.

(i) Methane

Explanation:

Marsh gas is a mixture of methane (CH₄), hydrogen sulfide (H₂S) and carbon dioxide (CO₂).

(ii) Single covalent bond configuration.

Explanation:
The water molecule is chemically written as:

H—O—H

Nitrogen has the electronic configuration 2, 5. It shares 3 of the outermost electrons with another nitrogen atom to form a triple-bonded N₂ molecule, as shown below:

Covalent compounds have strong forces of attraction within the molecule, but the inter-molecular forces are very small due to which they are volatile. This results in the low melting and boiling point of compounds making them volatile.

In the crystalline form of carbon, many atoms are bonded together in a repeating pattern. The arrangement of atoms in the crystal differs for each form of carbon. Two forms are:

i. Diamond.
Each carbon atom is covalently bonded to four other carbon atoms. The arrangement of carbon is shown below:

ii. Fullerene:
each carbon atom is covalently bonded to four other carbon atoms. Each sphere contains 60 carbon atoms, and each carbon atom is bonded to three others by single covalent bonds.

In diamond, each carbon atom is covalently bonded to four other carbon atoms.

The crystal structure is shown below:

Diamond has a 3D structure.

In graphite, each carbon atom is bonded to 3 other carbon atoms in the same plane giving rise to a hexagonal array. The structure of graphite is formed by stacking these hexagonal layers over one another and these layers have weak inter-molecular forces.

This structure results in the smoothness of graphite.

Artificial diamonds can be artificially prepared by subjecting pure carbon to a very high temperature and pressure.

Note:
Here is a description of the complete process for extra knowledge.

Diamond has a rigid 3D structure in which each carbon atom is covalently bonded to 4 other carbon atoms. This structure involves a network of strong C-C bonds which requires high energy to break the bonds. Hence, the diamond has a high melting point.

The ability of an element to form bonds with other atoms of the same element is called catenation.

The different types of bond chains are:

Carbon forms a large number of compounds because (a) Carbon exhibits catenation to a very large extent. It can form long chains, branched chains or ring structures.

(b) Carbon has a valency of 4. It is satisfied by forming single, double or triple bonds with carbon or other elements such as oxygen, hydrogen, nitrogen etc. The bonds formed are strong and hence the compounds formed are stable.

C₃H₈ contains 3 carbon atoms and 8 hydrogen atoms.

Now, each carbon atom has 4 electron and each hydrogen atom has 1 electron each.

So, in total 3×4 + 1×8 = 12 + 8 = 20 electrons.

And, 1 single bond = 2 electrons.

∴ 10 single bonds.

There now plot the electrons on the atoms as shown, and then jin the single bonds.

This is the final structure of propane i.e. C₃H₈

There are 9 isomers for heptane (C₇H₁₆):

a. 2-methyl hexane (isoheptane)

b. n-heptane

c. 3-methylhexane

d. 2,2-dimethylpentane

e. 2,3-dimethylpentane

f. 2,4-dimethylpentane

g. 3,3-dimethylpentane

h. 2,2,3-trimethylbutane

i. 3-ethylpentane

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

Eaxample: Methane (CH₄) and ethane (C₂H₈).

There are a part of homologous series & the difference among these molecules is that they have different numbers of CH₂ groups.

(i) Molecular mass

(ii) International Union of Pure and Applied Chemistry

In IUPAC nomenclature, the following subdivision is followed for naming the compounds.

Primary suffixes are used to indicate the degree of unsaturation (i.e., presence of double or triple bonds) in a carbon compound.

e.g.: -ane (for alkanes), -ene (for alkenes), -yne (for alkynes)

Secondary suffixes are those suffixes which describe the main functional group of the compound. They are added after the primary suffix.

e.g.: -one (for ketones), -oic acid (for carboxylic acids)

Example:

Unsaturated hydrocarbons give sooty flame after burning even in sufficient amount of oxygen. Saturated hydrocarbons may give sooty flame upon burning if there is limited supply of oxygen.

(i) complete oxidation (in the presence of strong oxidizing agents like acidified potassium dichromate)

(ii) aldehydes

Bromine water can be used for the test of unsaturation. If bromine water which is brown in colour is added to unsaturated compounds, then bromine water gets decolourised as a result of addition reaction.

Saturated compounds do not decolourise bromine water.

Example:

Combustion is the process of burning of a substance in the presence of oxygen. The fuel (coal or petroleum) gets oxidized. As a result, the bonds present in the molecules of fuel break, releasing energy. Sometimes, the energy released falls in the visible range of the electromagnetic spectrum (which means the energy released is visible to human eye) which we call as light. Sometimes the energy released falls under infrared region, which we commonly call as heat. Basically, the compounds generate heat or light or both due to the release of energy from the breaking of molecular bonds.

When ethyl alcohol reacts with sodium metal, hydrogen gas is liberated along with the formation of sodium ethoxide.

Methanol and acetone are added to denature the alcohol to prevent the misuse of alcohol.

Ethanoic acid is used as a preservative in pickles.

It is also used in the production of esters which are used in making perfumes and as flavouring agents.

When soap is added to water, it forms clusters of molecules called micelles. These soap micelles are large enough to scatter light and therefore makes the soap solution cloudy.

Graphite is the allotrope of carbon used for lubrication purposes.

Diamond is the hardest naturally occurring substance in the world. Its hardness is made use of in making knives to cut marbles.

The general formula of alkenes is C_nH_2n, where ‘n’ is the number of carbon atoms.

Here, C₂H₄ and C₃H₆ are alkenes (put n=2, 3)

The minimum number of carbon atoms to form a branched compound should be 4; 3 in the parent chain and 1 in the branched chain. The compound is 2-methylpropane (isobutane).

CH₄O, C₂H₆O belong to the same homologous series as they differ only by a –CH₂ unit.

The successive members of a homologous series differ by a –CH₂ unit.

Propyl chloride

The molecular formula is C₄H₈O₂.

This is an example of addition reaction.

Carboxylic acid (-COOH) can be detected by using sodium hydrogen carbonate (NaHCO₃) test. Treating a carboxylic acid with NaHCO₃ causes effervescence due to the liberation of carbon dioxide (CO₂). The reaction is as follows:

R-COOH + NaHCO₃→ R-COONa + CO₂ + H₂O

In graphite, each carbon is covalently bonded to 3 other carbon atoms in a hexagonal arrangement. That is 3 out of 4 valence electrons are used for covalent bonding. The remaining 1 electron from each carbon atom is free (or delocalized). This free electron helps in the conduction of electricity.

The given sample of water contains calcium ions and hence is hard water. Soaps are not effective in hard water as they produce scum (insoluble precipitate) with calcium ions. Therefore, synthetic detergents must be used to clean the dirt of clothes in hard water.

Homologues of CH₃CH₂OH: CH₃CH₂CH₂OH (propanol), CH₃CH₂CH₂CH₂OH (butanol),...

Homologues of HCOOH: CH₃COOH (ethanoic acid), CH3CH₂COOH (propanoic acid),...

(i) Propanone (ii) ethyne

(i) –COO^- group (carboxylic acid; the anion is called carboxylate ion)

(ii)ester group ()

(iii) –OH group – alcohol

(iv) –CHO group - aldehyde

Methanoic acid contains 1 C=O bond and 1 C-O bond.

The general molecular formula of a carboxylic acid is C_nH_2nO₂.

Vegetable oils contain unsaturated fatty acids which are good for the health, whereas vegetable ghee contains saturated fatty acids which are harmful to our health.

Vegetable oils are converted into ghee by the process of hydrogenation. Hydrogen is added to unsaturated compounds in the presence of a catalyst (such as nickel) to produce saturated compounds. The reaction is illustrated as:

The water content present in acetic acid provided in the laboratory is higher than that of glacial acetic acid.

Pure ethanoic acid is often called glacial acetic acid because it freezes to form ice-like crystals when kept in cold surroundings (the melting point is 290K).

Inlets are provided to supply air to ensure that the fuel burns completely and give a clean flame. If the inlets are absent, then the fuel may not burn completely and produce sooty flame. This will also result in wastage of fuel.

To determine whether a given water sample is of hard water or soft water, one can use soap.

Soap produces lather in soft water whereas soap does not produce lather in hard water due to the formation of scum (insoluble precipitate). Scum is a result of reaction of soap with calcium and magnesium ions present in the hard water.

In the reaction of esters with alkali to prepare soap (saponification reaction), the product (soap) is obtained in a suspension form. To precipitate the soap out of the suspension form, common salt (NaCl) is added to it. This process is often referred to as “salting out” of soap.

Yes, soap can be used for washing clothes in water containing sodium bicarbonate, as sodium ion will not contribute to the hardness of water.

Non-sooty flame can be interpreted as clean flame. Clean flame is given out by burning of saturated compounds. Hence, A is propane (C₃H₈).

(i) C is a covalent compound, as the combining atoms form a bond by sharing of electrons.

(ii) Using “like dissolves like” rule, polar molecules dissolve in polar solvents, whereas non-polar molecules dissolve in non-polar solvents. C and organic solvents are both covalent (non-polar) in nature, but water is a polar solvent. Hence C will dissolve in organic solvents.

(i) Saturated hydrocarbons undergo substitution reaction through a mechanism called “free radical mechanism”, where the initial step of reaction is the formation of free radicals. Generation of free radicals requires sunlight, without which the reaction does not get initiated. So, sunlight is necessary for the substitution reactions of saturated hydrocarbons.

(ii) Ethyne (HC≡CH) is an unsaturated compound, and unsaturated compounds produce yellow sooty flame with lots of black smokes. This is due to incomplete combustion of ethyne in air.

(i) Ethanoic acid provides an acidic environment where bacteria cannot survive, preserving the pickles for a longer time.

(ii) Both diamond and graphite are allotropes of the same element carbon. The only difference is in their physical properties due to the difference in their structure. The chemical properties remain the same. Carbon when burnt in the presence of oxygen gives carbon dioxide (CO₂). Since, diamond and graphite are chemically carbon, both release CO₂ upon burning.

X is ethanoic acid (CH₃COOH). It is acidic and hence turns blue litmus red. It releases carbon dioxide (CO₂) when treated with Na₂CO₃ and NaHCO₃ which is responsible for effervescence.

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

CH₃COOH + NaHCO₃→ CH₃COONa + CO₂↑ + H₂O

(i) Carbon has the ability to form long, branched chains or ring structures with other carbon atoms. This self-linking capacity is referred to as catenation.

Also carbon has a valency of 4 and combines with 4 other monovalent atoms or shares its outermost electrons with different elements through single, double or triple bonds. The bonds formed are highly strong and stable. Hence carbon forms a large variety of compounds.

(ii) Compounds of carbon which are linked by only single bonds between the carbon atoms are called saturated compounds.

Compounds of carbon having double or triple bonds between the carbon atoms are called unsaturated compounds.

(iii) Unsaturated compounds are more reactive than saturated compounds because of the presence of double or triple bonds present in them. These bonds tend to break in the presence of some reacting species to become saturated compounds which are highly stable. The relative stability of hydrocarbons in the decreasing order is given by:

alkanes > alkenes > alkynes

The molecular formula of ethene is C₂H₄. The three succeeding members in this homologous series are:

Propene (C₃H₆), Butene (C₄H₈), Pentene (C₅H₁₀)

(i) A + B → C

The above reaction occurs because the stability of C is higher than the stability of A and B. Molecules always tend to attain the most stable configuration in a reaction.

Here saturated compounds are more stable than unsaturated compounds. The double/triple bonds present in the unsaturated compound break to form single bonds by combining with the reactant to attain a highly stable product. Therefore, unsaturated hydrocarbons show addition reaction.

(ii) Alcohol supplied for industrial purpose is mixed with chemicals like methanol to prevent the misuse of it. It is a common practice to overuse this alcohol for recreational purposes, and addition of these chemicals would help prevent the misuse to an extent. To identify such mixtures of alcohols, dyes or coloured substances are added to colour the alcohol blue. In this case, the coloured substance added is copper sulphate.

(i) 3-methylpentane

(ii) pentanoic acid

(i) Petroleum or crude oil is called black gold and it is formed from the remains of plants and animals that lived in the sea millions of years ago. The dead remains along with the silt which settled in the sea bed are attacked by bacteria and got converted to crude oil and gas under high pressure conditions. Slowly the silt compressed into rocks and the oil seeped into the porous parts of the rocks.

(ii) Fossil fuels such as coal and petroleum contain some amount of nitrogen and sulphur in them. The combustion of these fuels in air results in the formation of oxides of nitrogen and sulphur which are major pollutants of the environment. Therefore, coal and petroleum are considered to be pollutants of air.

The substance X is ethanol (C₂H₅OH).

The acidic nature of acetic acid can be shown using:

(a) Litmus test – Chemicals which are acidic in nature turn blue litmus red

(b) Sodium carbonate test – Acids when treated with sodium carbonate gives effervescence due to the liberation of carbon dioxide. Acetic acid also produces CO₂ in this reaction.

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

Esters are prepared by the reaction of an acid and an alcohol in the presence of an acid catalyst. The reaction is called esterification reaction.

Esters are sweet smelling substances and hence are used in making perfumes and as flavouring agents.

X is ethanol (C₂H₅OH) and Y is ethanoic acid (C₂H₄O₂)

Acetic acid (CH₃COOH) is a weak acid and belongs to the family of carboxylic acids.

Physical Properties:

Acetic acid exists in liquid state at room temperature. Pure acetic acid has a melting point of 290K and often freezes when kept in cold climates.

Chemical Properties:

(a) Reaction with alcohol:

Acetic acids react with alcohols in the presence of an acidic medium to form esters. Esters are sweet smelling substances and are often used in perfumes and as flavouring agents.

(b) Reaction with base:

Like other acids, acetic acid reacts with base to form salt and water. The reaction is called neutralization reaction.

(c) Reaction with carbonates and bicarbonates:

Acetic acid reacts with carbonates and bicarbonates to form salt, carbon dioxide and water.

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

CH₃COOH + NaHCO₃→ CH₃COONa + CO₂↑ + H₂O

The versatility of carbon can be explained in the following ways:

(a) Catenation:

The self-linking capacity of an element is referred to as catenation. Carbon can form long straight chains, branched chains, or ring structures by bonding with other carbon atoms. No other element exhibits catenation up to this extent. Carbon can link with other carbon atoms using single, double or triple bonds.

(b) Tetravalency:

Carbon has a valency of 4. It is satisfied by forming bonds with 4 other monovalent atoms. Carbon can also form multiple bonds (double or triple bonds) with atoms like oxygen and nitrogen. The bonds formed are highly stable and thus forms stable compounds.

(i) The structural formula of the two compounds are shown below.

2,2-dimethylpropane

2-methylbutane

Note that both compounds have the same molecular formula C₅H₁₂. Since they have same molecular formula but different structural formula, they are isomers.

(ii) Ethane (C₂H₆) and propane (C₃H₈) can be represented by the general formula C_nH_2n+2 where ‘n’ is the number of carbon atoms. Also they differ by a –CH₂ unit. Hence they are homologues.

(iii) C₂H₅Cl and C₃H₇Cl differ by a –CH₂ unit. Also these 2 can be represented by the formula C_nH_2n+1Cl. Therefore they are homologues.

(iv) C₃H₄ is an alkyne and C₂H₄ is an alkene. Both the compounds contain double or triple bonds. Therefore, they belong to the family of unsaturated compounds.

(i)

(ii)

(iii)

(iv)

(v)

(vi)

(vii)

(viii)

(ix) Glycerol is propane-1,2,3-triol

(x)

Hydrogenation is the process of addition of hydrogen to compounds containing double/triple bonds to form saturated compounds.

The hydrogenation of unsaturated carbon compounds is given by the reaction:

Catalyst is a substance which alters the rate of a chemical reaction, without undergoing any change to itself. Nickel, palladium can be used as the catalyst for hydrogenation.

Vegetable oil must be chosen for cooking as it contains unsaturated fatty acids which are good for health.

(i) Ethanol upon combustion gives carbon dioxide and water.

C₂H₅OH + 3O₂→ 2CO₂ + 3H₂O

(ii) Ethanol is oxidized to ethanoic acid when treated with oxidizing agents like acidified potassium dichromate

(iii) Ethanol reacts with sodium metal to liberate hydrogen gas.

2C₂H₅OH + 2Na → 2C₂H₅O^-Na⁺ + H₂

(iv) Ethanol when dehydrated using conc. H₂SO₄ forms ethene.

(v) Ethanol (C₂H₅OH) reacts with ethanoic acid (CH₃COOH) in the presence of acidic medium to produce ethyl ethanoate which is an ester.

A – ethyl ethanoate

B – ethanol

C – sodium ethanoate

D – ethanoic acid

Esters upon alkaline hydrolysis gives back the carboxylic acid and the alcohol. The acid is initially obtained in its salt form. The reaction is called saponification.

The salt (sodium ethanoate) is treated with dil HCl to obtain the carboxylic acid.

Ethanol is oxidized to ethanoic acid in the presence of acidified potassium dichromate. Here, the acid used for acidification is H₂SO₄.

(i) The hardness of water can be determined using soap.

If the given amount of soap has difficulty in producing foam (lather) and produces an insoluble precipitate (scum) instead, in the water then the water is hard.

If the soap produces foam easily in the water, then the water is soft.

(ii) Hard water contains calcium and magnesium ions. Scum is formed as a result of reaction between calcium or magnesium ions with soap.

(iii) The problem of scum formation can be avoided by using detergents. The charged ends of these compounds do not form insoluble precipitates with calcium or magnesium ions in hard water which makes detergents effective in hard water.

From this, one can learn that soaps are ineffective in hard water (water containing calcium and magnesium ions) as they do not produce foam in hard water. This is rectified by the usage of another class of compounds called detergents. Thus one must not use soaps in hard water, as it will be a waste of time and money. At the same time one must also realize that detergents are non-biodegradable. These compounds cannot be degraded by bacteria and therefore can potentially harm the environment.

Graphite is commonly used as an abrasive, but diamond is not used.

The number of neutrons in carbon atoms present in both graphite and diamond are the same. It only depends upon the nature of the element, and both are allotropes of the same element carbon.

In diamond, each carbon is covalently bonded to 4 other carbon atoms whereas in graphite, each carbon is covalently to 3 other carbon atoms.

Graphene is an allotrope of carbon. Like diamond, and graphite, when subjected to sufficient supply of air, it burns to release carbon dioxide.

As you go down a group, the size of the atom increases and the ionization enthalpy decreases due to the shielding of outermost electrons by the inner electrons.

All the three compounds are alkanes and can be generally represented by C_nH_2n+2, where ‘n’ is the number of carbon atoms.

Number of C-H bonds = 10 = 10 bond pairs (bp) of electrons

Number of C-C bonds = 3 = 3 bp of electrons

Number of C-O bonds = 2 = 2 bp of electrons

Number of C=O bonds = 1 = 2 bp of electrons

Total number of bp = 10+3+2+2 = 17

C₂H₄ is an alkene which is an unsaturated compound. It gives addition reaction.

C₅H₁₀ is an alkene which is an unsaturated hydrocarbon. Only unsaturated hydrocarbons react with hydrogen to form saturated hydrocarbons.

Only unsaturated carbon compounds produce yellow (and sooty) flame. C₆H₁₄ is a saturated compound (hexane) and it will always produce clean blue flame (not yellow) when burnt in sufficient amount of oxygen.