Page 31 - Focus SPM KSSM F4 2020 - Chemistry

Chemistry Form 4 Chapter 3 The Mole Concept, Chemical Formula and Equation
(a) What is the meaning of relative atomic mass? [1 mark]
(b) Give one reason why carbon-12 is used as the standard atom to compare the mass of an atom?
[1 mark]
(c) Based on Figure 3.24, state the relative atomic mass of element Y. [1 mark]
(d) In an investigation, Y reacts with bromine gas to form the compound YBr .
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(i) Write the chemical equation for the reaction. [1 mark]
(ii) Interpret the chemical equation in 2(d)(i) quantitatively. [1 mark]
(iii) Using the relative atomic mass of element Y from your answer in 2(c), calculate the number of moles
of bromine gas required to react completely with 3.6 g of Y. [2 marks]
(IV) In another investigation, 9.6 g of Y reacts with 6.4 g of oxygen. Complete the table below to determine
the empirical formula of the oxide of Y.
[Relative atomic mass: O, 16]

Element Y O Chapter

Mass (g)
3
Number of moles of atoms

Simplest ratio of moles
[3 marks]

Section B
2. (a) The following is the description of P, Q and R. The letters are not the real symbol of the elements.

• One P atom has twice the mass of one Q atom.
• Ten P atoms has equal mass with seven R atoms.
• Relative atomic mass of P is 28

(i) Determine the relative atomic masses of Q and R. Then, arrange the elements in an ascending order
of relative atomic mass. [3 marks]
(ii) Explain why a sample of 14 g of P has equal number of atoms as that in a 20 g sample of of R.
[4 marks]
(iii) R is a reactive metal that can react with oxygen to form metal oxide. Describe briefly how you can
determine the empirical formula of metal R oxide in the laboratory. [7 marks]
(b) Hydrocarbon W consists of 92.3% carbon and 7.7% hydrogen by mass. The relative molecular mass of
hydrocarbon W is 26. Determine the empirical formula and molecular formula of W.
[Relative atomic mass: H,1; C,12] [6 marks]

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