1. Simple tests carried out on organic chemicals in a laboratory can be very informative - Leaving Cert Chemistry - Question 1 - 2020
Question 1
1. Simple tests carried out on organic chemicals in a laboratory can be very informative.
(a) Ethene (C2H4) is a colourless, gaseous, unsaturated hydrocarbon. To co... show full transcript
Worked Solution & Example Answer:1. Simple tests carried out on organic chemicals in a laboratory can be very informative - Leaving Cert Chemistry - Question 1 - 2020
Step 1
What colour is the bromine solution used in the test?
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The bromine solution used in the test is brown, specifically it can appear in shades of red, orange, or yellow.
Step 2
What change is observed when the gas bubbled through the bromine solution is unsaturated?
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Answer
When the unsaturated hydrocarbon ethene is bubbled through bromine solution, the brown colour of the bromine fades and eventually becomes colourless, indicating a reaction has taken place.
Step 3
What is meant by an unsaturated hydrocarbon?
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An unsaturated hydrocarbon is characterized by having at least one double or triple bond between carbon atoms. This structural feature means it can undergo additional reactions, adding more atoms to its structure.
Step 4
Describe how you carried out a combustion test on a sample of ethyne provided in a stopped test tube.
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To carry out the combustion test, I securely clamped the test tube containing ethyne and removed the stopper. I then inserted a lit taper into the mouth of the test tube, ensuring that it was safe to allow the ethyne to ignite.
Step 5
Describe the flame observed.
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The flame observed was bright, luminous, and sooty, producing smoke. This indicates a potentially incomplete combustion due to the carbon content in ethyne.
Step 6
Give a reason for your choice.
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I would choose batch Y, as its melting point (120–122°C) is higher, indicating that it is likely purer than batch X (117–120°C), which presents a wider range and a lower average melting point.
Step 7
Benzoic acid's purity can be more soluble in what?
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Benzoic acid can be more soluble in hot water than in cold water due to its increased solubility at higher temperatures.
Step 8
Name the method that could have been used to further establish each batch on this fact.
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The method that could be used is recrystallization. This process helps to purify the benzoic acid by dissolving it in a hot solvent and then cooling to form pure crystals.
Step 9
Match soap
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A: soap - Lather forms
Step 10
Match clove oil
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B: clove oil - White emulsion forms
Step 11
Match ethanolic acid
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C: ethanolic acid - Bubbles of gas form
Step 12
Match ethanol
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D: ethanol - A brick-red precipitate appears
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