8.1 When a piece of sodium metal (Na) is added to water in a test tube, hydrogen gas is released - NSC Physical Sciences - Question 8 - 2021 - Paper 2
Question 8
8.1 When a piece of sodium metal (Na) is added to water in a test tube, hydrogen gas is released. When phenolphthalein indicator is added to the test tube, the solut... show full transcript
Worked Solution & Example Answer:8.1 When a piece of sodium metal (Na) is added to water in a test tube, hydrogen gas is released - NSC Physical Sciences - Question 8 - 2021 - Paper 2
Step 1
8.1.1 Define the term reduction in terms of electron transfer.
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Answer
Reduction is defined as the gain of electrons during a chemical reaction. In the context of electron transfer, this means that a species gains one or more electrons, resulting in a decrease in its oxidation state.
Step 2
8.1.2 Write down the reduction half-reaction.
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The reduction half-reaction for the reaction involving sodium metal can be represented as:
ightarrow H_2(g) + 2OH^-(aq)$$
Step 3
8.1.3 Write down the balanced equation for the reaction that takes place.
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The balanced equation for the overall reaction when sodium metal is added to water is:
ightarrow H_2(g) + 2NaOH(aq)$$
Step 4
8.1.4 Give a reason why the solution turns pink.
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The solution turns pink due to the formation of sodium hydroxide (NaOH), which is a strong base. The phenolphthalein indicator turns pink in alkaline (basic) solutions as it changes color at a pH above 7.
Step 5
8.1.5 Refer to the relative strengths of the REDUCING AGENTS to explain why no reaction is observed.
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Copper does not react with water because it is a weaker reducing agent than hydrogen. When copper is added to water, it fails to displace hydrogen ions, leading to no observable reaction.
Step 6
8.2.1 What does the single line (|) in the cell notation above represent?
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Answer
The single line (|) in the cell notation represents a phase boundary between different states of matter. In this case, it separates the solid lead (Pb) from the aqueous lead ions (Pb2+).
Step 7
8.2.2 State the energy conversion that takes place in this cell.
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The energy conversion in this electrochemical cell is the conversion of chemical energy into electrical energy. This occurs when the redox reactions at the electrodes generate a flow of electrons.
Step 8
8.2.3 Calculate the initial emf of the cell under standard conditions.
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To calculate the initial emf (electromotive force) of the cell, we can use the standard reduction potentials. For the overall reaction, we have:
