(i) When ethanol is heated with excess of concentrated sulphuric acid at 443K, it gets dehydrated to form ethene.
\(\underset { Ethanol }{ { CH }_{ 3 }-{ CH }_{ 2 } } OH\xrightarrow [(Dehydration) ]{ conc. H_2SO_4;443K } \underset { Ethene }{ { CH }_{ 2 }={ CH }_{ 2 } } +H_2O\)
In this reaction, concentrated sulphuric acid acts as a dehydrating agent which removes water molecules from the ethanol molecule.

Esterification: It is a process in which alcohol and carboxylic acid combine in the presence of cone. H₂SO₄ to form ester.
\(\underset{Ethanoic\ acid}{CH_3COOH}+\underset{Ethanol}{C_2H_5OH}\xrightarrow{conc.H_2SO_4}\underset{Ethyl\ ethanoate}{CH_3COOC_2H_5}+H_2O\)
Saponification: When an ester reacts with sodium hydroxide, sodium salt of acid and alcohol is formed.
\(\underset{Ethyl\ ethanoate}{CH_3COOC_2H_5}+\underset{Sodium\\ hydroxide}{NaOH}\rightarrow \underset{Sodium\\ ethanoate}{CH_3COONa}+\underset{Ethanol}{C_2H_5OH}\)
Uses:
(i) Esters are used in cold drinks, ice creams, perfumes and as artificial flavouring agents.
(ii) Saponification process is used in the manufacture' of soaps. 

Alkaline potassium permanganate of acidified potassium dichromate.
(i) Ethanol will not affect litmus paper Ethanoic acid will turn blue litmus paper red.
(ii) Ethanol will not react with sodium hydrogen carbonate. Ethanoic acid will give brisk effervescence due to colourless, odourless carbon dioxide gas.

Those compounds, which have same molecular formula but different structural formulae are called isomers.

In first three members of alkane series, branching is not possible. Therefore, we cannot have isomers.

(i) When ethanol is heated with copper at 573K, ethanal is formed.

(ii) When ethanol is oxidised with alkaline potassium permanganate solution, ethanoic acid is formed.
\(\underset{Ethanol}{CH_3CH_2OH}+2[O]\xrightarrow[KMnO_4]{Alkaline}\underset{Ethnoic\ acid}{CH_3COOH}\)

A is ethanol (C₂H₅OH) which is essential constituent of wine and beer and 'B' is acetic acid (CH₃COOH) which is present in vinegar.
\(\underset{(Present\ in\ wine\ and\ beer)\\ 'A'}{CH_3CH_2OH}+2[O]\xrightarrow[Oxidation]{Alkaline\ KMnO_4}\underset{Acid\\ (Present\ in\ vinegar)\\ 'B'}{CH_3COOH}+H_2O\)
When 'A' and 'B' react in the presence of an acid catalyst, ethyl ethanoate is formed.
 \(\underset{'A'}{CH_3COOH(l)}+\underset{'A'}{C_2H_5OH(l)}\xrightarrow{Conc. H_2SO_4} CH_3COOC_2H_5(l)+H_2O(l)\)

Homologous series is a series of organic compounds which have same functional group and similar chemical properties. Each member of this series differs by - CH₂ - in its molecular formula and 14 u in its molecular mass.
C₂H₆O(C₂H₅OH) and CH₄O(CH₃OH) belong to same homologous series.

It is ethanol, its molecular formula is C₂H₆O.
Ethanol forms ethene, when heated with conc. H₂SO₄.
\(CH_3 \underset { Ethanol }{CH_2 }OH \xrightarrow [heat ]{ Conc.H_2SO_4 } \underset { Ethene }{CH_2= CH_2 }+H_2O \)

(a) Functional group is an atom or group of atoms or reactive part of compound, which determines chemical properties of compounds.
(i) -OH (Alcohol)
(ii) -COOH (Carboxylic acid)
(b) Soaps do not work well with hard water, detergents work well with hard water.

Molecular Formula of Ethyne: C₂H₂ 
Electron dot structure of Ethyne:

Structural formula of Ethyne 
HC≡CH

Hard water contains calcium and magnesium ions. Soap is basically sodium or potassium salt of higher fatty acids. When soap is added to hard water, corresponding calcium and magnesium salts are formed, which being insoluble gets precipitated. These precipitates are called scum. Reactions taking place are shown as:
Ca²⁺          + 2RCOONa \(\rightarrow\) (RCOO)₂ Ca\(\downarrow\) + 2Na⁺
Hard water      Soap               Calcium salt precipitate
Mg²⁺ + 2R COONa \(\rightarrow\) (RCOO)₂Mg \(\downarrow\) + 2Na⁺
Hard water  Soap           Magnesium salt precipitate 

The formula for cyclopentane is C₅H₁₀. Its electron dot structure is

Alcohol and carboxylic acid can be distinguished experimentally by two reactions:
(i) Reaction with Base
Alcohols do not react with base like NaOH, KOH while carboxylic acids react with base to form salt and water.
e.g. CH₃COOH + NaOH \(\rightarrow\) CH₃CO\(\bar{O}\)\(\overset{+}{N}\)a + H₂O
CH₃CH₂OH + NaOH \(\rightarrow\) No reaction
(ii) Reaction with Sodium bicarbonate
Carboxylic acids react with sodium bicarbonate rapidly to give brisk effervescence of CO₂ gas while alcohols do not react.
e.g. CH₃COOH + NaHCO₃ \(\rightarrow\) CH₃COONa + H₂O + CO₂\(\uparrow\)
CH₃CH₂OH + NaHCO₃ \(\rightarrow\) No reaction

We need a high temperature for welding but when ethyne is burnt in air, it undergoes incomplete combustion and releases a lot of smoke and the temperature is also not very high. In order to ensure complete oxidation and to obtain the high temperature needed for welding, a mixture of ethyne and oxygen is used.
2CH \(\equiv\) CH + 5O₂ \(\rightarrow\) 4CO₂ + 2H₂O + Heat + Light