Page 50 - Spotlight A+ Form 4 & 5 Chemistry KSSM

(iii) Sodium chloride, NaCl cannot conduct electricity in solid state but it can conduct electricity in
aqueous state. Explain why. [2 marks]
(b) Figure 7.2 shows the symbol of two elements, N and H. Element N reacts with element H to form a
compound.
14 N 1 H
7 1
Figure 7.2
(i) State the type of particle in the compound formed. [1 mark]
(ii) Draw a diagram to show the electron arrangement in the compound formed between atoms N
and H. [2 marks]
(iii) The molecule formed in (b)(ii) can combine with hydrogen ion, H to form ammonium ion,
+
NH . State the type of chemical bond and explain briefly how the chemical bond is formed.
+
4
[2 marks]
8. (a) Figure 8.1 shows three test tubes contain dilute H X acid, HY acid and dry glacial ethanoic acid,
2
CH COOH. H X acid and HY acid are strong acids.
3 2
P Q R

0.1 mol dm 0.1 mol dm Anhydrous
–3
–3
dilute H X acid dilute HY acid ethanoic acid,
2
CH COOH
3
Calcium carbonate, Calcium carbonate, Calcium carbonate,
CaCO
CaCO
CaCO
SPM MODEL PAPER ©PAN ASIA PUBLICATIONS
3
3
3
Figure 8.1
There are no gas bubbles produced in test tube R. Suggest a method that can make calcium
(i)
carbonate, CaCO reacts with ethanoic acid, CH COOH to produce gas bubbles.
[1 mark]
3
3
(ii) Table 8 shows the pH value of aqueous solution of ethanoic acid, CH COOH and dilute HY acid
3
of the same molarity.
Type of acid
0.1 mol dm
Molarity Ethanoic acid Dilute HY acid
–3
0.1 mol dm
–3
pH value 4.0 1.0
Table 8
Explain why the pH value of aqueous solution of ethanoic acid, CH COOH is higher than the
3
pH value of dilute HY acid. [2 marks]
(iii) Figure 8.2 shows the apparatus set up for the titration of 20 cm of 0.5 mol dm sodium
–3
3
hydroxide, NaOH solution with H X acid of an unknown concentration. Phenolphthalein is
2
used as the indicator.
H X acid
2
Sodium hydroxide, NaOH
solution + phenolphthalein
Figure 8.2
The chemical equation for the reaction is as the following.
H X(aq) + 2NaOH(aq) → Na X (aq) + 2H O(l)
2 2 2
3
If 25 cm of H X acid is required to neutralise the sodium hydroxide, NaOH solution in the
2
conical flask, calculate the concentration of the H X acid solution in mol dm . [3 marks]
–3
2
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