A student prepared and collected ethene (C₂H₄) gas using the arrangement of apparatus and chemicals shown below - Leaving Cert Chemistry - Question 1 - 2018
Question 1
A student prepared and collected ethene (C₂H₄) gas using the arrangement of apparatus and chemicals shown below. A few stopped test-tubes of the gas were kept to exa... show full transcript
Worked Solution & Example Answer:A student prepared and collected ethene (C₂H₄) gas using the arrangement of apparatus and chemicals shown below - Leaving Cert Chemistry - Question 1 - 2018
Step 1
Identify the white solid A.
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Answer
The white solid A is aluminium oxide (Al₂O₃).
Step 2
Describe the appearance of the gas collected.
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The gas collected is colourless, which can also be described as clear.
Step 3
Explain why the first few test-tubes of gas collected are not then used.
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The initial test-tubes of gas are likely to contain impurities or a mixture of air and ethene, due to the displacement of air during collection.
Step 4
There is a risk of suck-back while carrying out this experiment.
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Suck-back occurs when there is a sudden drop in pressure that causes liquid from the apparatus to be drawn back into the delivery tube.
Step 5
What is suck-back hazardous?
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Suck-back can be hazardous as it may lead to the breaking of glassware or contamination of the gas with liquid, potentially causing dangerous reactions.
Step 6
What precaution should be taken to avoid suck-back?
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To avoid suck-back, a break in vacuum should be made by breaking the vacuum with water or by removing the delivery tube before allowing heating or cooling effects.
Step 7
Identify a reagent used to test ethene for unsaturation.
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Bromine (Br₂) solution is a common reagent used to test for unsaturation in ethene.
Step 8
What colour change is a positive result in using the reagent you identified?
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The positive result shows a colour change from red/orange to colourless, indicating a reaction has occurred.
Step 9
How was the combustion test carried out?
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The combustion test was conducted by inserting a splint or match into the test-tube which was then ignited.
Step 10
Describe the flame observed.
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The flame was bright yellow, luminous, and very clean, although slightly smoky.
Step 11
Complete and balance the following equation for the complete combustion of ethene in oxygen:
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The complete and balanced equation is: C₂H₄ + 3O₂ → 2CO₂ + 2H₂O.
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