Correct Answer: B. Iodine crystals molecules are held together by weak forces

Correct Answer: C) its vapour pressure equals the external pressure

Explanation

Boiling is the process by which a liquid turns into a gas as it is heated. This occurs when the temperature of the liquid is high enough for its molecules to have enough energy to overcome the attractive forces holding them together. In simpler terms, the molecules in the liquid move more rapidly, and some of them gain enough energy to escape as gas.

The vapour pressure of a liquid is the pressure exerted by its vapour when it is in equilibrium with the liquid. As the temperature of a liquid increases, its vapour pressure also increases. When the vapour pressure of the liquid becomes equal to the external pressure (usually atmospheric pressure), the liquid starts to boil.

This means that boiling points can vary depending on the external pressure. For example, at high altitudes, where the atmospheric pressure is lower, liquids boil at lower temperatures than they do at sea level.

Correct Answer: C) decreasing the temperature and increasing the pressure

Correct Answer: A. 1s₂2s₂2p₅

Correct Answer: C. hygroscopic

Correct Answer: A. spherical

Correct Answer: C. can start a chemical rection which will normally not take place

Explanation

(a)(i) Characteristic properties of electrovalent compounds.

- They do not contain molecules

- They dissolve in water to form electrolyte

- They have high melting or boiling point

- They are mostly inorganic compounds

(ii) Alpha particles: They are positively charged

- They have low penetrating power

- They exert a very powerful ionizing effect upon any gas through which they pass.

(iii) Catalysts : Catalysts remain unchanged in chemical nature and in mass at the end of a reaction.

- Catalysts alter the rate of a chemical reaction

- They are specific in action

- Catalysts cannot initiate or start a reaction

- They have no effect on the equilibrium of a reversible reaction.

(b)(i) \(_{14}\)Si - 1S\(^2\)2S\(^2\) 2P\(^6\)3S\(^2\)3P\(^2\). Silicon belongs to group four in the periodic table.

(ii) Bond between silicon and oxygen is covalent.

(iii) 1 mole of silicon has a mass of 28 and 6.02 x 10\(^{23}\) atom, in 5.72 x 10\(^{-3}\) g.

= \(\frac{5.72 \times 10^{-3}}{28}\) x 6.02 x 10\(^{23}\)

= 1.2298 x 10\(^{20}\).

(c)(i) X is a good reducing agent because it will react with water to liberate hydrogen.

(ii) X is best stored under oil.

(iii) X will react with cold water to liberate hydrogen gas. It is a violent reaction.

(iv) X\(_2\)O + 2HCI \(\to\) 2XCI + H\(_2\)O.

(v) The likely colour of the salt of X is white.

Explanation

(a)(i)

(ii) Two uses of each of the following compounds:

(1) Sodium Chloride - food seasoning, food preservative, glazing pottery/earthen ware. soap production, crude oil refilling, water softener, production of chlorine/hydrogen/ sodium metal, NaOH/NaClO\(_3\)/NaOCl/Na\(_2\)CO\(_3\) lowering melting point of ice preparation of freezing mixture. Used in tannery industry/tanning.

(2) Uses of sodium trioxocarbonate (IV) - Manufacture of glass/borax in detergents/ soaps, manufacture of paper softening hardwater, manufacture of NaOH treating (concentrated) acid splash, standardization of acids/analytical reagent.

(b)(i) Balanced equations for the reactions involved in the extraction of iron in the blast furnace.

C\(_{(g)}\) + O\(_{2(g)}\) ----> CO\(_{2(g)}\)

CO\(_{2(g)}\) + C\(_{(g)}\) --> 2CO\(_{(g)}\)

Fe\(_{2}\)O\(_{3}\) + 3CO\(_{(g)}\) \(\to\) 2Fe + 3CO\(_{2(g)}\)

CaO + SiO\(_{2}\) -> CaSiO\(_{3}\)

CaCO\(_{3}\) -> CaO + CO\(_{2}\)

(ii) Faraday's first law of electrolysis states that the mass of an element discharged at the electrode is directly proportional to the quantity of electricity passed through the electrolyte.

(iii) Two applications of electrolysis are: Electroplating of metals, Extraction of metals, Purification of metals, Preparation of compounds/elements, Production of gases H\(_{2}\), O\(_{2}\), Cl\(_{2}\) (any 2)

(c) Sugar crystals + concentrated H\(_{2}\)SO\(_{4}\) in a beaker. Observations are as follows:

(1) Concentrated acid dehydrates the sugar.

(2) A mass of carbon/black soot/ sugar charcoal is formed.

(3) Reaction is exothermic (heat evolved or released).

(d) Equations for the reaction of Zinc powder with dilute tetraoxosulphate (VI) acid:

(i) Zn\(_{(g)}\) + H\(_{2}\)SO\(_{4(aq)}\) -> ZnSO\(_{4(aq)}\) + H\(_{2(g)}\)

(ii) Reaction with dilute concentrated H\(_2\)SO\(_4\)

(iii) Zn\(_{(g)}\) + 2H\(_2\)SO\(_{4(aq)}\) -> ZnSO\(_{4(aq)}\) + SO\(_{2(g)}\) + 2H\(_2\)O\(_{(l)}\)

(e) Property of concentrated tetraoxosulphate (VI) acid shown in (d)(1) is oxidizing property.

Correct Answer: B) Calcium Oxide