Page 16 - Q & A STPM 2022 Chemistry

Chemistry Term 1 STPM Chapter 1 Atoms, Molecules and Stoichiometry
1.3 The Mole and the Avogadro Constant

Section A Multiple-choice Questions

Question 1
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Which of the following gases occupies the largest volume at standard
temperature and pressure? [Relative atomic mass: H = 1, C = 12, N = 14,
O = 16, Cl = 35.5]
A 8.0 g methane C 20.0 g nitrogen
B 16.0 g oxygen D 30.0 g chlorine Term

Answer: C 1
Exam Tips
Exam Tips
Determine the number of moles of each compound. Number of moles of gas
is directly proportional to its volume (n ∝ V ).
8.0
In A, the number of moles of CH 4 = —– = 0.5
16
16.0
In B, the number of moles of O 2 = —— = 0.50
32
20.0
In C, the number of moles of N 2 = —— = 0.71
28
30.0
In D, the number of moles of Cl 2 = —— = 0.42
71
Question 2
0.78 g potassium is completely burnt in excess chlorine vapour. The solid product
is then dissolved in 200 cm of 0.20 mol dm sodium chloride solution. What is
3
–3
the concentration of chloride ions in the solution?
[Relative atomic mass: K = 39, Cl = 35.5]
A 0.02 mol dm C 0.20 mol dm
–3
–3
B 0.05 mol dm D 0.30 mol dm –3
–3
Answer: D
Exam Tips
Exam Tips
Write a balanced equation for the reaction between potassium and chlorine.
2K + Cl 2 : 2KCl
Number of moles of Cl ions formed from KCl
–
0.78
= number of moles of K = —— = 0.02
39
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01 STPM Q&A Chem T1 layout.indd 11 4/19/19 9:28 AM