Page 18 - ACE YR IGCSE A TOP APPROACH TO CHEM

(d) Explain why potassium chloride has a high melting point.

[2]

(e) Solid potassium chloride cannot conduct electricity, but molten potassium chloride is a
good conductor of electricity. Explain why.

Penerbitan Pelangi Sdn Bhd. All Rights Reserved.

[2]

(f) Potassium oxide is also an ionic compound.

(i) It has a different ratio of positive and negative ions for the formation. For potassium
oxide, the ratio of potassium ions to oxide ions is 2 : 1. Explain why.

[3]
(ii) Potassium oxide is a base. Suggest a physical test to show it is a base.

test :

result :
[2]
[Total: 14]

3 Carbon dioxide is needed for photosynthesis. It takes up 0.03% of the air composition.

(a) Carbon dioxide is a gas at room temperature. Explain why.

[1]

(b) Carbon atoms and oxygen atoms are bonded together to form carbon dioxide.

(i) What kind of bonding is formed?

[1]
(ii) Use a dot-and-cross diagram to show the electron arrangement in a molecule of
carbon dioxide. Show only the outer shell electrons.

[3]

Chapter 2 Atoms, Elements and Compounds 15

Chapter 2.indd 15 3/4/22 11:59 AM