Explanation

(a)(i) Two elements which react with steam to produce hydrogen are Fe, Zn, Al, Mg (any two).

(ii) An aqueous solution of KBr turned reddish brown on bubbling chlorine through it because the chlorine oxidized the KBr / displaced the bromine from KBr. The free bromine coloured the solution.

(iii) Equation for the reaction involved in (a)(ii) Cl\(_2\) + 2KBr --> 2KCI + Br\(_2\)

(b)(i) Types of chemical industries that use limestone as raw materials: Iron/steel/iron and steel/metallurgical industry, paper industry, cement industry, glass industry, fertilizer industry.

(ii) Examples or hygroscopic substances CuO\(_2\) Conc. H\(_2\)SO\(_4\) . CaO alumina, silica gel (any one)

(c)(i) The SO\(_2\) is obtained by burning sulphur in air or roasting sulphide ore in air: S + O\(_2\) -> SO

(ii) The equation for the reaction in the catalyst chamber is 2SO\(_2\) + O\(_2\) --> 2SO\(_3\).

(iii) The steps required to core SO\(_3\) to acid arc:

- Dissolution in conc. H\(_2\)SO\(_4\) to form oleum. Or 2SO\(_3\) + H\(_2\)SO\(_4\) --> H\(_2\)S\(_2\)O\(_7\).

- Dilution of oleum with calculated amount of of water. Or H\(_2\)S\(_2\)O\(_7\) + H\(_2\)O --> 2H\(_2\)SO\(_4\)

(d)(i) Wastes soap, causes furl in pans and kettles / scales in boilers, results in burst pipes/narrow tubes in boilers, reduces heat capacity of boilers, makes dirty marks on clothes during washing or dying (any two).

(ii) Methods that remove both temporary and permanent hardness in water simultaneously.

- Addition of washing soda ((Na\(_2\)CO\(_3\)).

- Distillation.

- Use of cation exchange resins / permutit / zeolite

(iii) Role of alum in purification of water is coagulation. Role of chlorine in purification of water is killing of bacteria, germicide / sterilization

Explanation

a)(i) An acid-base indicator is either a weak organic acid or base which gives different colours in an acidic or basic mediurn. (Organic dye which changes colour according to the pH/hydrogen ion concentration of the solution).

(ii) Example of an acid-base indicator is: (i) phenolphthalein. (ii) methyl red. (iii) methyl orange. (iv) methyl yellow (v) alizarin yellow. (vi) litmus paper/solution. (vii) methyl violet. (viii) bromothymol blue (ix) bromocresol green.

(b) Property exhibited by nitrogen (IV) oxide in each of the following equations:

(i) 4Cu + 2NO\(_2\) —> 4CuO + N\(_2\), NO\(_2\) is an oxidizing agent

(ii) H\(_2\)O + 2NO\(_2\) —> HNO\(_3\) + HNO\(_3\), NO\(_2\) is oxidizing agent as well as a reducing agents or NO\(_2\) serves as acid anhydride or mixed anhydride.

(c)(i) Enthalpy of combustion is the amount of heat evolved or liberated when one mole of a substance is burnt mpletely in excess oxygen.

(ii) Enthalpy of combustion is always negative because heat is always given out or the action is exothermic.

(d) To distinguish between primary cell and secondary cell.

(i) (a) Primary cells cannot be recharged while secondary cells can be recharged.

(b) Primary cells do not last long while secondary cells last long.

(c) Reactions in primary cells are not reversible while reactions in secondary cells are reversible.

(ii) Examples of each of the cells in 1(d)(i). Primary cell: radio battery, dry cell, alkaline battery, button battery, Le'clanche cells, Daniel cell, torch battery, clock battery, bicycle lamp battery (any of these).

Secondary cell: lead-acid (storage - cell), lead-acid accumulator, lithium-ion battery, battery in rechargeable lamp, car battery, nickel-metal hydride cell, phone battery, nickel-cadmium cell, (hydrogen-oxygen) fuel cell, aluminium air cell/battery (any of these).

(e) Mole is defined as the amount of substance containing 6.02 x10\(^{23}\) particles of that substance as present in 12g of carbon-12 or the amount of substance containing as many elementary entities as there are atoms in 12g of carbon-12.

(f) Amount of hydrochloric acid in 40.0cm\(^{3}\) of 0.40 mo/dm\(^{3}\) dilute HCl

n = CV; C = concn in mo/dm\(^{3}\)

n = 0.40 x \(\frac{40}{1000}\); V = volume in dm\(^{3}\)

n(mol) = 0.016mol; n = amount in mol

(g) Two substances used as electrodes during electrolysis of acidified water are: graphite (carbon) and platinum.

(h) Two forces of attraction that can exist between covalent molecules

(1) Van der waals' forces or induced dipole-dipole forces.

(2) Hydrogen bonds.

(3) Permanent dipole-dipole interactions or dipolar forces (any of the two):

(i) Products formed when butane undergoes incomplete combustion are carbon (ii) oxide and water.

(j) Electron configuration of \(_{26}\)Fe\(^{3+}\)

\(_{26}\)Fe; Fe - 3\(\bar{e}\) \(\to\) Fe\(^{3+}\) lost of 3 electrons

\(_{26}\)Fe 26 protons + 26 electrons

\(_{26}\)Fe\(^{3+}\) 26 protons + 23 electrons

\(_{26}\)Fe\(^{3+}\) \(\to\) 1s\(^2\), 2s\(^2\), 2p\(^6\), 3s\(^2\), 3P\(^2\), 3d\(^5\)

Correct Answer: A. increases polarity

Correct Answer: D. Addition reaction

Explanation

Alkanols can be formed from alkenes through an addition reaction. In this reaction, the carbon-carbon double bond of the alkene is broken, and a hydroxyl group (-OH) is added to one of the carbon atoms, resulting in the formation of an alcohol.

Correct Answer: D. Gas

Explanation

Chlorine gas exists in the gaseous state at room temperature (around 25 degrees Celsius) and standard pressure.

Correct Answer: C. NO₂' O₂ and H₂O

Correct Answer: C. destroy bacteria and algae

Correct Answer: B. n-heptane

Correct Answer: B. crystallization.

Explanation

Crystallization is a separation technique that exploits differences in the solubilities of components in a solution. When a solution is allowed to cool or evaporate under controlled conditions, one of the salts may begin to crystallize out of the solution before the other due to its lower solubility. This process can be used to separate the salts based on their differing solubilities and crystal formation.

Correct Answer: D. cannot be regenerated once used up