Question

A. Give one word or a phrase for the following. [2 marks]
(i) The energy released when an electron is added to a neutral gaseous isolated atom to form a negatively charged ion.
(ii) Process of formation of ions from molecules which are not in ionic state.

B. How will you distinguish between ammonium hydroxide and soidum hydroxide using copper sulphate solution? [2 Marks]

C. Give a reason for each of the following. [3 marks]
(i) Ionic compounds have a high melting point.
(ii) Ionisation potential increases across a period, from left to right.
(iii) Conductivity of dilute hydrochloric acid is greater than that of acetic acid.

D. Arrange the following as per the the instruction given in the brackets: [3 marks]
(i) He, Ar, Ne (In the increasing order of the number of electron shells)
(ii) K, Pb, Ca , Zn (In the increasing order of the reactivity)
(iii) Na, K, Li (In the increasing order of atomic size)

Answer 1

A. (i) Electron affinity [1mark]
(ii) Ionisation [1 mark]

B. Ammonium hydroxide when added to copper sulphate drop-wise forms a pale blue ppt. of copper hydroxide which dissolves in excess of ammonium hydroxide to form a deep blue solution.
[1 mark]
Sodium hydroxide when added to copper sulphate drop-wise forms a pale blue precipiate which is insoluble in excess sodium hydroxide. [1 mark]
C. (i) Ionic compounds have high melting points because there is a strong electrostatic force of attraction between the oppositely charged ions and hence a large amount of energy is required to break the strong bonding force between ions. [1 mark]

(ii) On the periodic table, ionisation energy generally increases as you move left to right across a period. This is due to increasing nuclear charge, which results in the outermost electron being more strongly bound to the nucleus.

(iii) Acetic acid is weak electrolyte which dissociates partially whereas HCl is strong electrolyte which dissociates completely. Therefore, conductivity of dilute hydrochloric acid is greater than acetic acid.

D. (i) When we go down the group in the periodic table, the electron shells are added to the elements. We can also say that, in successive periods, the electron shell number increases by one. Hence the order of elements according to the increase in number of electron shells is as follows, He < Ne < Ar. [1 mark]

(ii) The reactivity series of metals, also known as the activity series, refers to the arrangement of metals in the descending order of their reactivities.
So, the correct order is: Pb < Zn < Ca < K. [1 mark]

(iii) We know that atomic size increases from right to left and from top to bottom in the Periodic Table. So the correct order of atomic radius is Li < Na < K. [1 mark]