Page 31 - ACE YR IGCSE A TOP APPROACH TO CHEM

(c) Blow carbon dioxide into limewater [1]
turn cloudy [1] O
Limewater is calcium hydroxide. When carbon
dioxide reacts with calcium hydroxide, calcium O Si O
carbonate is formed. Calcium carbonate is a
precipitate that turns the solution cloudy. O
(d) Carbon dioxide:
• Simple covalent compound 5 (a) + + – + + – + – +
–
• Intermolecular forces / van der Waals forces – – + – + – + – – + – + – +
–
are weak. + – + – + – + – + – + –
–
–
–
• Less energy to overcome. – + – + – + – + + – – +
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Copper(II) oxide: – – –
• Ionic compound A regular arrangement [1]
• Ionic bond is strong. of positive ions [1]
• More energy to overcome. and a sea of electrons / delocalised electrons. [1]
Note: Mark is only given if the following has been
mentioned for both compounds. (b) Has delocalised electrons / free moving electrons
Type of compound [1] [1]
Type of bonding [1] (c) Any two from: [2]
Level of energy required to break the bonds [1] • Shiny
• High density
4 (a) Giant covalent structure [1] • High melting point / boiling point
(b) Diamond: • Malleable / Ductile
• Each carbon atom is bonded to four other • Sonorous
carbons. • Strong
• Tetrahedron (d) Particles are arranged in layers. [1]
Graphite: Particles can slide over each other. [1]
• Each carbon atom is bonded to three other (e) (i) Mixture of a metal with another or more
carbons. metals (or non-metals). [1]
• Layers of hexagonal shape
Note: Show comparisons [2] (ii) Zinc [1]
(iii) More useful / Its properties are improved.
(c) Graphite has free moving electrons. [1] [1]
Diamond has no free moving electron. [1]
6 (a) (i) T and X [2]
(d) Any one from: [1] Valency of an element is the number of
• Diamond is harder. / Graphite is softer. electrons its atoms lose or gain or share, to
• Diamond has a higher melting point. / form a compound.
Graphite has a lower melting point. T = 2,8,2, T formed 2 +
• Diamond is denser. / Graphite is less dense. X = 2,8,6, X formed 2 –
Note: Word of comparison must be used. So, they have the valency of 2.
(e) Any one from: [1] (ii) S [1]
Diamond: Br has a valency of 1. It loses 1 electron to
form Br . To form an ionic compound, charges
–
• Tools for drilling / cutting should be cancelled out.
• Jewellery S = 2,8,1. It has a valency of 1. It forms S .
+
+
–
Any one from: [1] 1 mole of S reacts with 1 mole of Br to form
Graphite: an ionic compound with a 1 : 1 ratio.
• As a lubricant (iii) V [1]
• Pencil V = 2,8,4. V has a valency of 4. It can share the
• Electrode 4 electrons with 4 halogens to form a covalent
compound.
(f) Each silicon atom is bonded to four oxygen (iv) W [1]
atoms. [1] W = 2,8,5. W has a valency of 3. It will gain 3
Each oxygen atom is bonded to two silicon electrons to form W .
3–
atoms. [1] (v) Y [1]
Tetrahedron [1] Y has the number of protons 17. The number
of protons is equal to the number of electrons.
So, the electronic configuration is 2,8,7.

Answers 143

Answers.indd 143 3/4/22 3:54 PM