Achievement Test 2 (Textbook) (Question 1 – 3) – Chemistry Form 4 Chapter 2 (Matter and the Atomic Structure)

Question 1:
Table 1 shows the melting point and boiling point of substances A, B, C, D and E.


(a) Classify substances A, B, C, D and E according to states of matter at room temperature.

(b) State the substance that will change from liquid to solid when placed in the freezer at temperature 2 °C.

(c) Describe the changes that take place on the particles of substance B with relation to energy and attraction force between particles when cooled from 80 °C to –2 °C.


Answer:
(a)


(b) Substance C

(c) Substance B changes from gas to liquid. The kinetic energy of substance B particles decreases. The attraction force between the particles become stronger.

Question 2:
A group of students carried out an experiment to determine the melting point of lauric acid, C₁₂H₂₄O₂.

Figure 1 shows the heating curve obtained.


(a) Copy Figure 1 and label the melting point of lauric acid, C₁₂H₂₄O₂ on the diagram.

(b) Draw the arrangement of particles in lauric acid, C₁₂H₂₄O₂ between R and S.

(c) The melting point of lauric acid, C₁₂H₂₄O₂ is 43 °C.
Suggest a suitable method of heating lauric acid, C₁₂H₂₄O₂.

(d) Draw a labelled diagram to show the set-up of apparatus for the method suggested in (c).


Answer:
(a)

(b)



(c) Water bath

(d)

Question 3:
Chen Ling cleans her wound using alcohol as shown in Photograph 1. Chen Ling’s skin feels cool when wiped with alcohol. Explain this situation.


Answer:
Alcohol evaporates when it is rubbed onto the skin. Heat is absorbed from the skin by alcohol particles causing Chen Ling to feel cold.