(a) Define the following terms:
(i) Acid
(ii) pH scale
(iii) Neutralisation.

(b) (i) Outline the steps that would be necessary to convert insoluble lead (II) oxide into insoluble chloride.
(ii) Write the balanced equations for the reaction required to convert insoluble lead (II) oxide into insoluble lead chloride.
(iii) If iron reacts with dilute sulphuric acid, what will be the products?
(iv) A solution of iron (III) chloride has a pH less than 7. Is the solution acidic or alkaline?

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Solution

(a)
(i) Acids are compounds that generate hydronium ions (the only positively charged ions) when they get dissolved in water. Examples include hydrochloric acid (HCl) and sulphuric acid ( $H_{2} {SO}_{4}$ ).

HCl + H₂O ⇌ H₃O⁺+ Cl^-

(ii) pH scale is defined as the scale of acidity that is used to determine the acidic or basic (alkaline) nature of a solution. On the pH scale, bases (or alkalis) have a pH value greater than 7, while acids have a pH value less than 7. Neutral solutions have the pH value 7.

(iii) The reaction between an acid and a base to form a salt and water is called neutralisation reaction. For example, hydrochloric acid reacts with sodium hydroxide to form sodium chloride and water.

NaOH + HCl →NaCl + H₂O
Normal salt

(b) (i) and (ii) Preparation of lead chloride from lead oxide involves the following steps:

Step I: Lead (II) oxide (insoluble) is treated with dilute nitric acid to form soluble lead nitrate.

PbO + 2HNO₃→ Pb(NO₃)₂ + H₂O
Insoluble Soluble

Step II: Lead nitrate is then treated with hydrochloric acid to form insoluble lead (II) chloride and water.
Pb(NO₃)₂ + 2HCl→PbCl₂ + 2HNO₃
Insoluble

(iii) When iron metal reacts with dilute sulphuric acid, it forms iron (II) sulphate or ferrous sulphate and releases hydrogen gas.

$Fe + dil . H_{2} {SO}_{4} \to {FeSO}_{4} + H_{2}$

(iv) On the pH scale, bases (or alkalis) have a pH value greater than 7, while acids have a pH value less than 7. Therefore, iron (III) chloride solution with a pH value less than 7 is acidic in nature.

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Write a balanced chemical equation with state symbols for the following reactions.

(i) Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride.

(ii) Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution and water.

Q. (a) Write the balanced equations for the preparation of the following compounds (as the major product), starting from iron and using only one other substance:
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