Carbon And Its Compounds

The general molecular formula of an alkane is written as C_nH_2n+2, and the general formula of an alkene is written as C_nH_2n where ‘n’ is the number of carbon atoms.

Now for n=20, the molecular formula of

a) alkane will be C₂₀H_2x20+2 or C₂₀H₄₂

b) alkene will be C₂₀H_2x20 or C₂₀H₄₀

The compound is ethanol (C₂H₅OH). Ethanol is used as a fuel in certain places as it is cleaner, and would give rise to only carbon dioxide and water on burning in the sufficient amount of air.

One can observe that the given compounds belong to the “alkyne” family, where the molecular formula can be generally represented as C_nH_2n-2. Here, ‘n’ denotes the number of carbon atoms.

For a molecule with 5 carbon atoms, n=5 and hence the molecular formula will be C₅H_2x5-2 or C₅H₈ (pentyne)

Carboxylic acids are compounds where one or more hydrogen atoms are replaced by the -COOH group:

Note that every carboxylic acid contains 2 O (oxygen) atoms. The carboxylic acids with no other functional groups have the molecular formula C_nH_2nO₂.

Using this, one can say that C₂H₄O₂ (ethanoic acid) and C₃H₆O₂ (propanoic acid) are carboxylic acids.

Consider the following reaction:

Note that one double bond is hydrogenated using 1 mole of H₂.

∴ if there are 2 double bonds in the vegetable oil, then 2 moles of H₂ will be required for complete hydrogenation of 1 mole of the oil.

Ethanol (C₂H₅OH) is used in cough syrups and tonics because it is a very good solvent.

Ethanol is harmful for drinking. Drinking ethanol in small amounts causes drunkenness. If it is consumed in large quantities, then it can slow down metabolic processes and affect the central nervous system. This will lead to lack of coordination, mental confusion, stupour etc.

When methanol is consumed, it is oxidised to methanal in the liver. Methanal reacts rapidly with the components of cell, leading to the coagulation of protoplasm. Consumption of methanol can also damage the optic nerve, resulting in blindness.

Given that A turns blue litmus red. So A is acidic in nature.

Brisk effervescence with NaHCO₃ indicates carbon dioxide as one of the products.

The molecular formula of A contains 2 oxygen atoms. So the compound is likely to be a carboxylic acid (general molecular formula is C_nH_2nO₂)

Here n=2 and hence the compound A is ethanoic acid. The reaction is given by:

CH₃COOH + NaHCO₃→ CH₃COONa + H₂O + CO₂

Detergents are cleansing agents which are ammonium or sulphonate salts of long chain carboxylic acids.

Synthetic detergents which consist of continuous chains of carbon are more biodegradable when compared to the branched-chain synthetic detergents.

The reactivity of elements is described by the tendency to attain noble gas configuration (to attain a completely filled outer shell).

Carbon has 4 electrons in its outermost shell. So to attain completely filled outer shell, it can choose to accept 4 additional electrons or lose the 4 valence electrons to have noble gas configuration, but this is extremely difficult as the above mentioned processes are energetically unfavourable.

To overcome the above issue(s), the valence electrons are shared with other atoms and these shared electrons belong to outer shells of both atoms. The bond so formed by sharing the valence electrons is called covalent bonding. This way both atoms form a molecule and attain noble gas configuration.

The general molecular formula of alkenes and alkynes containing ‘n’ number of carbon atoms is C_nH_2n and C_nH_2n-2.

Using this one can see that,

Alkenes: C₆H₁₂, C₂H₄, C₄H₈

Alkynes: C₃H₄, C₅H₈

Note that molecular formula alone is not sufficient to uniquely identify a compound. For example, C₆H₁₂ can mean hexane (unsaturated hydrocarbon) as well as cyclohexane (saturated cyclic hydrocarbon).

(i) Butene

(ii) Ethanal

(i) Butanone

(ii) Propan-2-ol

Here, the –OH group is attached to the second carbon. Count the carbon atoms such that the carbon containing the functional group gets the lowest number.

(iii) Methanoic acid

(iv) Methyl ethanoate

The carbon group (alkyl part obtained from alcohol) attached to O of –COO group (denoted by R’) is mentioned in the first part of IUPAC name.

The carbon chain obtained from carboxylic acid (denoted by R) is represented in the second part of the name (the –oate part).

Ethanol is a good solvent which makes it suitable for preparing medicines.

Concentrated sulphuric acid (conc.H₂SO₄) acts as a dehydrating agent in the conversion from ethanol to ethene. It helps in removing water molecule (more specifically, the –OH group from one carbon and –H from the other carbon) in the following reaction.

The strength of acid is determined by its ability to produce H⁺ in solutions. Unlike mineral acids, the carboxylic acids (of the form RCOOH) do not completely ionise. They partially ionise to give H⁺ and RCOO^-. Therefore they are called weak acids.

Methanol on oxidation in the presence of a strong oxidising agent like alkaline KMnO₄ produces methanoic acid.

(i) This is an example of neutralization reaction

CH₃COOH + NaOH → CH₃COONa + H₂O

(ii)

(iii) Alcohols will get oxidised to acids in the presence of MoO₃ which is an oxidising agent. In this case, methanol (CH₃OH) gets oxidised to methanoic acid (HCOOH).

(iv) CH₂ = CH₂ + Br → CH₂Br—CH₂Br

This is an example of addition reaction.

(v) CH₃COOC₂H₅ + NaOH → CH₃COOH + C₂H₅OH

This is an example of saponification reaction and is used in the preparation of soaps.

(vi)

This is an addition reaction, where H⁺ is added to one of the carbon and OH^- is added to the other carbon.

(i) Ethanol is added to petrol because ethanol is a cleaner fuel which when burnt in a sufficient amount of air to give carbon dioxide and water.

(ii) Ethanol is a good solvent and is widely used in cough syrups and tonics.

(iii) Vinegar is a commonly used preservative. It helps in storing food for a long time

(a) (i) A – CH₃CH₂COOC₂H₅

(ii) B – CH₃COOH

(iii) C – CH₄

(b) The compound X is benzene (C₆H₆). The structural formula is

Generally, bromine water gets decolourised when it is added to an unsaturated compound. But the double bonds in the benzene are delocalised which increases its stability or decreases its reactivity. Benzene will not undergo addition reaction with bromine water.

Therefore, benzene does not decolourise bromine water.

(a) The electron dot structure of ethene is

Ethene is a non-polar molecule and will not dissolve in water (polar solvent). Since it does not produce ions in water, ethene does not conduct electricity in aqueous solutions. Ethene is a covalent molecule and has low melting point.

(b) The compound X is butane.

Balanced equation for combustion of butane:

2C₄H₁₀ + 13O₂→ 8CO₂ + 10H₂O

Substitution reaction with Cl₂ in the presence of sunlight:

C₄H₁₀ + Cl₂→ C₄H₉Cl + HCl

C₄H₉Cl + Cl₂→ C₄H₈Cl₂ + HCl

The substitution reaction continues until all H is replaced by Cl.

(c) Vegetable oils contain unsaturated carbon chains whereas vegetable ghee contains saturated carbon chains which are said to be harmful to health.

Vegetable oils are converted into vegetable ghee by the process of hydrogenation in the presence of a catalyst like nickel.

(a) The most commonly used preservative in cold drinks is sodium benzoate which is the sodium salt of benzoic acid. Some carboxylic acids are also used as preservatives.

(b) Ethanoic acid (also called acetic acid) is present in vinegar.

(c) One can organise talk shows, or presentations regarding the health issues associated with junk food. If possible, posters and other articles could be shared among people using social media.

(d) Sipping from the same cold drink or biting the same burger by many students may result in spread of harmful bacteria and other microorganisms if one of the students is ill. Therefore it is advised not to do so.

(e) Yes, junk food should be banned from school canteen because it consists of artificial preservatives and additives which are harmful to our health. Moreover, continuous consumption of junk food and cold drinks may decrease the ability to control the appetite.

The advantages of using cloth bags over polythene bags include

(a) Polythene bags are practically non bio-degradable. The improper disposal of such bags would result in soil pollution. Cloth bags are bio-degradable and will not pollute the environment.

(b) Usage of cloth bags would promote the cottage industries which produce cloth bags.

(c) Cloth bags are more durable when compared to polythene bags.

(d) The production processes of polythene bags involve in the emission of harmful chemicals.