(a) i) Give the name and nature of the radiations... | WAEC SSCE - Chemistry - 2010

Question 1 Report

(a) i) Give the name and nature of the radiations that are emitted during radioactivity.

ii) State two differences between chemical reaction and nuclear reaction.

iii) Balance the following nuclear reactions and identify X and Y.

I. \(^{212}_{84} PO\) \(\to\) \(^{208}_{82} Pb\) + X

II \(^{137}_{55}Cs\) \(\to\) \(^{137}_{55}Ba\) + Y

(b) The electron configuration of an element X is: 1s\(^2\) 2s\(^2\) 2p\(^6\) 3s\(^2\) 3p\(^5\)

(i) Deduce the atomic number of X.

(ii) To what group does X belong?

(iii) Give two properties of the group to which the element X belong.

(iv) Identify element X by name.

(v) Write a balanced equation to represent the reaction between the element X and hot concentrated NaOH.

(c)(i) Explain why: I. graphite is used as a lubricant; II. diamond is used as an industrial cutting tool.

(ii) Write an equation to represent the reaction between aqueous HCI and NH\(_3\) solution.

(iii) Name the type of reaction represented by the equation.

Answer

(a) Radioactivity

(i) Radiations emitted: alpha (\(\alpha\)) radiation, positively charged helium nuclei; beta (\(\beta\)) radiation, negatively charged fast-moving electrons; gamma (\(\gamma\)) radiation, high-energy electromagnetic waves with no charge and no mass.
(ii) Two differences between chemical and nuclear reactions: a chemical reaction involves only the outer (valence) electrons and the atomic nucleus is unchanged, whereas a nuclear reaction involves the nucleus and the element is changed into a different element; the energy change in a nuclear reaction is enormously greater than in a chemical reaction. (Also: chemical reactions can be affected by temperature/pressure/catalyst; nuclear reactions cannot.)
(iii) Balancing:
- I. \(^{212}_{84}Po \to\ ^{208}_{82}Pb +\ ^{4}_{2}X\). Mass number: \(212-208 = 4\); atomic number: \(84-82 = 2\). So X is an alpha particle (\(^{4}_{2}He\)).
- II. \(^{137}_{55}Cs \to\ ^{137}_{56}Ba +\ ^{0}_{-1}Y\). Mass number unchanged (137); atomic number rises by 1 (55 to 56). So Y is a beta particle (\(^{0}_{-1}e\), an electron).

(b) Element X: \(1s^{2}2s^{2}2p^{6}3s^{2}3p^{5}\)

(i) Atomic number: total electrons \(= 2+2+6+2+5 = 17\).
(ii) Group: 7 valence electrons, so Group VII (17), the halogens.
(iii) Two properties of the group: they are reactive non-metals existing as diatomic molecules; they are strong oxidizing agents whose reactivity decreases down the group; they form ions of charge \(-1\) (and coloured, with characteristic states, e.g. Cl\(_2\) is a greenish-yellow gas).
(iv) Identity: X is chlorine.
(v) Reaction with hot concentrated NaOH: \[3Cl_2 + 6NaOH \to 5NaCl + NaClO_3 + 3H_2O\]

(c) Carbon and neutralization

(i) I. Graphite as a lubricant: graphite has a layered structure in which the flat layers are held together by weak forces, so the layers slide easily over one another, giving a slippery, lubricating action. II. Diamond as a cutting tool: in diamond every carbon atom is covalently bonded to four others in a rigid three-dimensional giant structure, making it extremely hard, so it can cut and grind other materials.
(ii) \[HCl_{(aq)} + NH_3{(aq)} \to NH_4Cl_{(aq)}\]
(iii) Type of reaction: neutralization (an acid-base reaction; also a combination reaction).

Answer Details

(a) Radioactivity

(i) Radiations emitted: alpha (\(\alpha\)) radiation, positively charged helium nuclei; beta (\(\beta\)) radiation, negatively charged fast-moving electrons; gamma (\(\gamma\)) radiation, high-energy electromagnetic waves with no charge and no mass.
(ii) Two differences between chemical and nuclear reactions: a chemical reaction involves only the outer (valence) electrons and the atomic nucleus is unchanged, whereas a nuclear reaction involves the nucleus and the element is changed into a different element; the energy change in a nuclear reaction is enormously greater than in a chemical reaction. (Also: chemical reactions can be affected by temperature/pressure/catalyst; nuclear reactions cannot.)
(iii) Balancing:
- I. \(^{212}_{84}Po \to\ ^{208}_{82}Pb +\ ^{4}_{2}X\). Mass number: \(212-208 = 4\); atomic number: \(84-82 = 2\). So X is an alpha particle (\(^{4}_{2}He\)).
- II. \(^{137}_{55}Cs \to\ ^{137}_{56}Ba +\ ^{0}_{-1}Y\). Mass number unchanged (137); atomic number rises by 1 (55 to 56). So Y is a beta particle (\(^{0}_{-1}e\), an electron).

(b) Element X: \(1s^{2}2s^{2}2p^{6}3s^{2}3p^{5}\)

(i) Atomic number: total electrons \(= 2+2+6+2+5 = 17\).
(ii) Group: 7 valence electrons, so Group VII (17), the halogens.
(iii) Two properties of the group: they are reactive non-metals existing as diatomic molecules; they are strong oxidizing agents whose reactivity decreases down the group; they form ions of charge \(-1\) (and coloured, with characteristic states, e.g. Cl\(_2\) is a greenish-yellow gas).
(iv) Identity: X is chlorine.
(v) Reaction with hot concentrated NaOH: \[3Cl_2 + 6NaOH \to 5NaCl + NaClO_3 + 3H_2O\]

(c) Carbon and neutralization

(i) I. Graphite as a lubricant: graphite has a layered structure in which the flat layers are held together by weak forces, so the layers slide easily over one another, giving a slippery, lubricating action. II. Diamond as a cutting tool: in diamond every carbon atom is covalently bonded to four others in a rigid three-dimensional giant structure, making it extremely hard, so it can cut and grind other materials.
(ii) \[HCl_{(aq)} + NH_3{(aq)} \to NH_4Cl_{(aq)}\]
(iii) Type of reaction: neutralization (an acid-base reaction; also a combination reaction).

(a) i) Give the name and nature of the radiations that are emitted during radioactivity. ii) State two differences between chemical reaction and nuclear rea...