(i) If H⁺ ion concentration is more, pH will be less and vice versa or pH of a solution is inversely proportional to H⁺ ion concentration or pH 52 log (H⁺).
(ii) This solution is neutral.
(iii) 1MNaOH solution.
(iv) When the pH in the mouth is below 5.5, bacteria present in the mouth produce acids by degradation of sugar and corrode the tooth enamel. It can be prevented by using tooth pastes which are generally basic.
(v) As hydronium [H₃O]⁺ ion.

(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.

The Substance which is used for making different shapes is Plaster of Paris.  Its chemical name is calcium sulphate hemihydrate \([CaSO_4.1/2H_2O].\) The two formula unit of \(CaSO_4\) share one molecule of water.  As a result, it is soft.  When it is left open for some time, it absorbs moisture from the atmosphere and forms gypsum, which is a hard solid mass.

\(\underset{Plaster\ of\ Paris}{​​CaSO_4.{1\over 2}H_2O}+1{1\over2}{H_2O}\rightarrow \underset{Gypsum}{CaSO_4.2H_2O}\)

The gas evolved at anode during electrolysis of brine is chlorine (G) When chlorine gas is passed through dry \(Ca(OH)_2\ (Y)\) produces bleaching powder (Z) used for disinfecting drinking water.
\(Ca(OH)_2+Cl_2\rightarrow CaOCl_2+H_2O\)
Since Y and Z are calcium salts, therefore X is also a calcium salt and is calcium carbonate.
\(CaCO_3+2HCl\rightarrow CaCl_2+CO_2+H_2O\)
\(Ca(OH)_2+CO_2 \rightarrow CaCO_3+H_2O\)

(i) An aqueous solution with pH value 7.0 is neutral in nature.

(ii) The pH value is given by the formula:

           \(pH=-log[H^+]\)

           \(pH+-(-2)\ log\ 10\)

or, pH = 2

(iii) 1 M NaOH solution has a higher pH value.  This because \(pH=-log[H^+]\ NaOH\) dissociates to give hydroxyl ion, not hydrogen ions.  On the other hand, HCl is a strong acid and dissociates to give hydrogen ions.

(i) The raw materials used in the manufacture of sodium carbonate by Solvay process are calcium carbonate \((CaCO_3)\),  ammonia gas \((NH_3)\), and sodium chloride solution \((NaCl)\).

(ii) Sodium hydrogen carbonate formed during Solvay process is separated from a mixture of \(NH_4Cl\) and \(NaHCO_3\) by the method of filtration.

(iii) Sodium carbonate is obtained from sodium hydrogen carbonate by heating it and then adding calculated amount of water into its.