When fresh milk turns into curd, its pH value will decrease.  This is because lactic acid is produced when decrease.  This is because lactic acid is produced when milk changes into curd.

Sodium carbonate.

Sodium hydroxide is a strong base. When excess base is dissolved in the solution of NaOH, the concentration of hydroxide ions (OH^-) per unit volume increases due to dissociation of NaOH as well as the other base in aqueous solution.
NaOH \(\overset{H_{2}O}{\rightleftharpoons}\) Na⁺ + OH^-
Any other base
e.g. M(OH)_x \(\overset{H_{2}O}{\rightleftharpoons}\) M⁺ + xOH^-

Acidic character of a compound is due to the presence of replaceable H⁺ ions, which are released in aqueous solution and are responsible for acidic properties. As HCI, HNO₃ etc have replaceable H⁺ ions, they show acidic character while glucose and alcohol do not have replaceable H⁺ ions, hence, no acidic character is shown by them.

(i) Increase in the strength of alkali. So the nature of solution will be basic.
(ii) Hydroxide ion or hydroxyl ion or OH^- ion.
(iii) A paper impregnated with the universal indicator is generally used to measure the pH of a solution.

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

(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.

Dilution of a concentrated acid is a highly exothermic reaction and a lot of heat is generated. Care must be taken while mixing concentrated acid with water. The acid must always be added slowly to water with constant stirring. If water is added to the concentrated acid, the heat generated may cause the mixture to splash out and cause burns. The glass container may also break due to excessive local heating.

(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.

Sodium hydroxide (NaOH) is a commonly used base and is hygroscopic, that is, it absorbs moisture from the atmosphere and becomes sticky.  The acidic oxides react with base to give salt and water. The reaction between NaOH and \(CO_2\) can be given as \(2NaOH+CO_2\rightarrow Na_2CO_3+H_2O\)

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.
\(CaCO_3+2HCl\rightarrow CaCl_2+CO_2+H_2O\)
\(Ca(OH)_2+CO_2 \rightarrow CaCO_3+H_2O\)