1. Ethyne (acetylene) gas (C2H2) is the first member of a homologous series of unsaturated hydrocarbons - Leaving Cert Chemistry - Question 1 - 2014
Question 1
1. Ethyne (acetylene) gas (C2H2) is the first member of a homologous series of unsaturated hydrocarbons. The diagram below shows the arrangement of apparatus used fo... show full transcript
Worked Solution & Example Answer:1. Ethyne (acetylene) gas (C2H2) is the first member of a homologous series of unsaturated hydrocarbons - Leaving Cert Chemistry - Question 1 - 2014
Step 1
Explain the term hydrocarbon.
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Answer
A hydrocarbon is a compound that consists solely of hydrogen (H) and carbon (C) atoms. Hydrocarbons can be classified into various categories based on their structure and types of bonds, such as saturated and unsaturated.
Step 2
To which homologous series does ethyne belong?
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Ethyne belongs to the homologous series known as alkynes, which are characterized by having at least one triple bond between carbon atoms.
Step 3
Identify
(i) the liquid A.
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The liquid A is water.
Step 4
Identify
(ii) the solid B.
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The solid B is calcium(II) dicarbide, also known as calcium carbide (CaC2).
Step 5
Identify
(iii) the liquid C.
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The liquid C is water.
Step 6
Why should the first few test-tubes of gas collected be discarded?
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The first few test-tubes of gas collected should be discarded because they may contain mostly displaced air and impurities rather than pure ethyne gas.
Step 7
What is meant by saying that ethyne is unsaturated?
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Ethyne is termed unsaturated because it contains at least one triple bond between carbon atoms, indicating that it can react with additional atoms to form new compounds, unlike saturated hydrocarbons that cannot accommodate more atoms.
Step 8
Describe a test that would show that ethyne is an unsaturated compound.
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To test for unsaturation, shake a sample of ethyne with a solution of bromine water (identified reagent). If ethyne is present, the reddish-brown color of bromine will disappear, indicating a reaction with the unsaturated compound.
Step 9
Describe the flame observed when a test-tube of ethyne is burned in air.
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When a test-tube of ethyne is burned in air, it produces a smoky and luminous flame due to the incomplete combustion of ethyne in the presence of limited oxygen.
Step 10
Give a use for this very hot flame.
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This very hot flame, produced by burning ethyne gas, is commonly used for cutting metals or welding due to its high temperature exceeding 3000°C.
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