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A student investigated the electrolysis of different substances - AQA - GCSE Chemistry - Question 6 - 2018 - Paper 1
Question 6
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A student investigated the electrolysis of different substances. Figure 6 shows the apparatus. Figure 6 dc power supply Graphite electrodes Solid zinc chloride ... show full transcript
Worked Solution & Example Answer:A student investigated the electrolysis of different substances - AQA - GCSE Chemistry - Question 6 - 2018 - Paper 1
Step 1
Explain why electrolysis would not take place in the apparatus shown in Figure 6.
Answer
Electrolysis would not take place because solid zinc chloride does not conduct electricity. In its solid form, the ions in zinc chloride are fixed in place within the crystalline structure and cannot move freely. Therefore, there are no mobile charge carriers available to facilitate the flow of electric current.
Step 2
Explain why graphite conducts electricity.
Answer
Graphite conducts electricity due to its unique structure and bonding. Each carbon atom in graphite forms three covalent bonds with other carbon atoms, creating a planar structure with layers. The fourth electron from each carbon atom is delocalized, allowing it to move freely throughout the structure. This movement of delocalized electrons enables the conduction of electricity within graphite.
Step 3
How should the apparatus be changed?
Answer
The apparatus should be changed by using measuring cylinders instead of test tubes. Test tubes cannot measure volume accurately since they do not have proper graduations, making it difficult to obtain precise volume measurements of the gases produced.
Step 4
Describe the trends shown in the results.
Answer
The results in Figure 8 show that the volume of hydrogen gas collected increases steadily over time, indicating that hydrogen is being produced at a consistent rate. In contrast, the volume of chlorine gas rises initially but then levels off, suggesting that while chlorine is being produced, its collection rate slows after a certain point. The trend indicates that up to around 8 minutes, chlorine is gathered at an increasing rate, but after that, it remains constant, similar to the volume rate of hydrogen collection.
Step 5
Suggest one reason for the difference in volume of each gas collected.
Answer
One reason for the difference in gas volumes collected is that chlorine gas may dissolve in the sodium chloride solution during the electrolysis process, while hydrogen gas does not dissolve significantly. This difference in solubility results in less chlorine gas being collected compared to hydrogen.
Step 6
Calculate the amount in moles of chlorine collected after 20 minutes.
Answer
To calculate the moles of chlorine gas collected, we first read the volume from Figure 8, which is approximately 6.6 cm³. We convert this volume to dm³: ext{Volume in dm³} = rac{6.6 ext{ cm}^3}{1000} = 0.0066 ext{ dm}^3
Next, to find the number of moles, we use the molar volume of a gas: ext{Moles} = rac{ ext{Volume in dm}^3}{ ext{Molar Volume (24.0 dm}^3 ext{)}}
Calculating this gives: ext{Moles of chlorine} = rac{0.0066}{24.0} = 2.75 imes 10^{-4} ext{ mol}
Thus, the amount of chlorine collected after 20 minutes is approximately .