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Sodium chloride, NaCl, is an ionic compound - OCR Gateway - GCSE Chemistry - Question 21 - 2019 - Paper 3
Question 21
Sodium chloride, NaCl, is an ionic compound. Sodium chloride forms a giant ionic lattice that can be represented using different models. Look at the diagrams. They s... show full transcript
Worked Solution & Example Answer:Sodium chloride, NaCl, is an ionic compound - OCR Gateway - GCSE Chemistry - Question 21 - 2019 - Paper 3
Step 1
Describe two limitations of using the ball-and-stick model for ionic compounds.
Answer
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The ball-and-stick model can misrepresent bond lengths and angles, making it difficult to accurately depict the structure of the ionic compound. This is because it assumes that ionic bonds are rigid when, in reality, the ions can vibrate and move within the lattice structure.
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The model may oversimplify the interactions between ions, as it does not account for the strengths of the ionic bonds or the presence of polarizability, which play a significant role in the stability of ionic compounds.
Step 2
Draw a dot and cross diagram to show the ions in sodium chloride.
Answer
To represent the ions in sodium chloride:
- Sodium ions (Na⁺) can be shown with a dot to represent its electron.
- Chloride ions (Cl⁻) can be shown with crosses to represent the electrons that were gained.
The diagram should depict one Na⁺ and one Cl⁻, with the dot from Na⁺ and the crosses from Cl⁻ clearly indicating the transfer of an electron.
Step 3
Explain the formation of the products during the electrolysis of potassium bromide solution.
Answer
During the electrolysis of potassium bromide (KBr) solution, two reactions occur at the electrodes:
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At the anode (positive electrode), bromide ions (Br⁻) are oxidized to form bromine gas (Br₂). This reaction involves the loss of electrons:
ext{2 Br}^- ightarrow ext{Br}_2 + 2 e^-
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At the cathode (negative electrode), potassium ions (K⁺) will typically remain in solution and water will be reduced instead, leading to the formation of hydrogen gas (H₂) and hydroxide ions (OH⁻):
ext{2 H}_2 ext{O} + 2 e^- ightarrow ext{H}_2 + 2 ext{OH}^-
As a result, bromine gas is evolved at the anode, while hydrogen gas is released at the cathode.