\(CaSO_4.{1\over 2}H_2O\)(Calcium sulphate hemihydrate)
When plaster of paris reacts with water
\(\underset{Plaster\ of\ Paris}{CaSO_4.{1\over 2}H_2O}+1{1\over 2}H_2O\longrightarrow\underset{Gypsum} {CaSO_4.2H_2O}\)

Green vitriol: FeSO₄.7H₂O
\(2FeSO_4(s) \xrightarrow{\Delta} Fe_2O_3(s) + SO_2(g) + SO_3(g)\)

\(2Fe{ SO }_{ 4 }\overset { Heat }{ \rightarrow } { Fe }_{ 2 }{ O }_{ 3 }+{ SO }_{ 2 }+{ SO }_{ 3 }\)
Crystals loose their color, due to loss of water of crystallization on heating.

Sodium sulphate is a neutral salt because it is made from strong acid and strong base.
Sodium carbonate is a basic salt because it is made from strong base and a weak acid.

Egg shells contain calcium carbonate When nitric acid is added to it, carbon dioxide gas is evolved. The reaction can be given as
\(CaCO_3+2HNO_3\rightarrow Ca(NO_3)_2+H_2O+CO_2\)

lons are produced only in aqueous medium and presence of H⁺ ions are responsible for the existence of acidic properties. Hence, acids show acidic behaviour only in the presence of water and not in its absence.

(i) pH = 6 has more H⁺ ion concentration.
(ii) Solution A having pH 6 is acidic.
Solution B having pH 8 is basic.

Dry HCl gas does not contain any H⁺ or H₃O⁺ ions, so it does not show any acidic property. Hence, it does not change the colour of dry litmus paper. To show its acidic behaviour, it needs wet litmus paper.

An acid molecule dissociates in an aqueous solution to produce H⁺ (or H₃,O⁺) ions and corresponding anions A. These free ions carry the electrical charge from one place to other, hence conduct electricity

(i) Tomato - Malic acid and citric acid
(ii) Vinegar - Acetic acid
(iii) Tamarind - Tartaric acid and citric acid.

pH in increasing order of H⁺ion concentration is C < E < D < A < B

(i) Universal indicator is a mixture of many different indications (or dyes) which give different colours at different pH values of the entire pH scale. The colour produced by the universal indicator is used to find the pH value of acid or base by matching the colour with the colours on pH colour chart.
(ii) Solution A is acidic and will turn litmus solution from blue to red.
Solution B is basic and will turn phenolphthalein from colourless to pink.
(iii) Green colour will be obtained.

(a) Concentrated sulphuric acid is called the king of chemicals as it is a very strong acid and is highly corrosive.

(b) The three chemical reactions that take place during the conversion of sulfur dioxide to sulphuric acid in the 'Contact Process' are given below.

Step I: Sulphur dioxide is mixed with air and passed over vanadiumpent (V) oxide catalyst heated to \(450^oC\) to form sulphur trioxide.

\(\underset{Sulphur\ dioxide}{2SO_{2(g)}}+\underset{Oxygen}{O_{2(g)}}\underset{\rightleftharpoons }{V_2O_5}\underset{Sulphur\ trioxide}{2SO_{3(g)}}+Heat\)

Step II : Sulphur trioxide is dissolved in concentrated sulphuric acid to form a thick fuming liquid called oleum.

\(\underset{Sulphuric\ acid}{H_2SO_4(l)}+\underset{Sulphur\ trioxide}{SO_{3(g)}}\begin{matrix} V_2O_5 \\ \rightleftharpoons \\ \end{matrix}\underset{Oleum}{H_2S_2O_{7(l)}}\)

Step III: Oleum is diluted with a calculated quantity of water to obtain sulphuric acid.

\(H_2S_2O_{7(l)}+\underset{Water}{H_2O_{(l)}}\rightarrow\underset{Sulphuric\ acid}{2H_2SO_{4(aq)}}\)

(c) If water is added to sulphuric acid then a large amount of heat is evolved.  This changes water to steam, which can splash the acid.  Hence, it is dangerous.