Page 34 - Spotlight A+ Form 4 & 5 Chemistry KSSM

Form
5
Chapter 1 Redox Equilibrium Chemistry
CHAP. CHAP.
+
1 4. The voltmeter reading is recorded. All (e) Hydrogen ions, H are reduced to form 1
observations at the electrodes are recorded.
hydrogen gas, H by gaining electrons.
2
5. Steps 1 to 4 are repeated using zinc, Zn plate Reduction occurs at the copper, Cu plate.
+
and copper, Cu plate. Hydrogen ion, H acts as oxidising agent.
(f) Electrons move from iron, Fe nail to copper,
Results: Cu plate through wire. In other words,
Table 1.10 electrons flow from reducing agent to the
oxidising agent. Therefore, iron, Fe nail
Voltmeter
Pair of Observations at the is an anode while copper, Cu plate is the
reading cathode of the voltaic cell.
metals electrodes
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(V) (g) Electrons that flow through the wire from
Iron, Fe 0.8 Iron, Fe nail becomes iron, Fe to copper, Cu produce electric
nail + thinner. current.
2. Zinc, Zn plate + copper, Cu plate:
copper, Gas bubbles are released (a) Oxidation half equation:
Cu plate around copper, Cu plate. 2+ –
Zn(s) → Zn (aq) + 2e
Zinc, Zn 1.1 Zinc, Zn plate becomes (b) Reduction half equation:
–
+
plate + thinner. 2H (aq) + 2e → H (g)
2
copper, Gas bubbles are released (c) Overall ionic equation:
Cu plate around copper, Cu plate. Zn(s) + 2H (aq) → Zn (aq) + H (g)
+
2+
2
(d) Zinc atom, Zn is oxidised to zinc ion, Zn
2+
Inference: by losing two electrons. Oxidation occurs
1. Iron, Fe nail and zinc, Zn plate dissolves and at the zinc, Zn plate and zinc, Zn acts as
corrodes to form iron(II) ion, Fe and zinc ion, reducing agent.
2+
2+
Zn respectively. (e) Hydrogen ions, H are reduced to form
+
2. Hydrogen gas, H is produced. hydrogen gas, H by gaining electrons.
2 2
Reduction occurs at the copper, Cu plate.
+
Conclusion: Hydrogen ion, H acts as oxidising agent.
Hypothesis is accepted. Two different metals that (f) Electrons move from zinc, Zn plate to
are dipped into an electrolyte and connected by copper, Cu plate through wire. In other
wire will produce electricity. words, electrons flow from reducing agent
to oxidising agent. Therefore, zinc, Zn plate
Discussion: is the anode while copper, Cu plate is the
1. Iron, Fe nail + copper, Cu plate: cathode of the voltaic cell.
(a) Oxidation half equation: (g) Electrons that flow through the wire from
Fe(s) → Fe (aq) + 2e – zinc, Zn to copper, Cu produce electric
2+
(b) Reduction half equation: current.
–
+
2H (aq) + 2e → H (g) 3. Reaction in the simple chemical cell is a redox
2
(c) Overall ionic equation: reaction because oxidation and reduction
2+
+
Fe(s) + 2H (aq) → Fe (aq) + H (g) occur at the same time.
2 4. If two copper, Cu electrodes are used, there
(d) Iron atom, Fe is oxidised to iron(II) ion, Fe is no potential difference between electrodes.
2+
by losing two electrons. Oxidation occurs When there is no electron flow, electric current
at the iron, Fe nail and iron, Fe acts as is not generated and voltmeter reading will
reducing agent.
show 0 V.

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