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Give a concise answer to each of the following questions - VCE - SSCE Chemistry - Question 5 - 2003 - Paper 1
Question 5
Give a concise answer to each of the following questions. a. The Downs Cell uses a molten electrolyte containing NaCl to produce sodium at an iron cathode. Explain ... show full transcript
Worked Solution & Example Answer:Give a concise answer to each of the following questions - VCE - SSCE Chemistry - Question 5 - 2003 - Paper 1
Step 1
a. The Downs Cell uses a molten electrolyte containing NaCl to produce sodium at an iron cathode. Explain why an aqueous solution of NaCl cannot be used to produce sodium at an iron cathode.
Answer
When using an aqueous solution of NaCl, water is also present, which can lead to the preferential reduction of water instead of sodium ions at the cathode. The reduction reactions can be represented as:
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Reduction of water:
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Reduction of sodium:
Since the reduction of water to hydrogen and hydroxide occurs at a lower electrode potential compared to sodium, sodium ions are not reduced, making aqueous NaCl unsuitable for sodium production.
Step 2
b. Alumina dissolved in molten cryolite is used in preference to molten alumina in the electrolytic production of aluminium. Explain why.
Answer
Molten cryolite significantly lowers the melting point of alumina, which helps in reducing the energy required for the electrolysis process. This is crucial since maintaining high temperatures for molten alumina alone would be inefficient. Additionally, cryolite improves the conductivity of the electrolyte, which enhances the efficiency of the operation. The energy savings achieved by using cryolite thus make it a preferred choice.
Step 3
c. If the tertiary structure of an enzyme is disrupted, the enzyme is no longer active. Explain why.
Answer
The tertiary structure of an enzyme is essential for maintaining its specific three-dimensional shape, which is critical for the enzyme's active site. The active site is the area that binds to the substrate molecules. If the tertiary structure is disrupted, the active site’s shape changes, rendering it unable to bind substrates effectively. This loss of specific shape directly correlates to a significant reduction in enzymatic activity.
Step 4
d. When a solution of the enzyme amylase is boiled at 100°C for several minutes, the enzyme loses its tertiary structure yet its primary structure remains intact. Explain why.
Answer
The primary structure of an enzyme, which consists of a sequence of amino acids linked by peptide bonds, is held together by covalent bonds. However, the tertiary structure is stabilized by non-covalent interactions such as hydrogen bonds, ionic bonds, and hydrophobic interactions. When amylase is boiled, these weak non-covalent interactions are disrupted due to the high temperature, leading to the denaturation of the enzyme's tertiary structure. Nevertheless, the covalent peptide bonds maintaining the primary structure remain intact, thus preserving the sequence of amino acids.