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NSWChemistryQuick questions

Module 7: Organic Chemistry

Quick questions on Alkanes, alkenes and alkynes explained: HSC Chemistry Module 7

10short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.

What is combustion (all hydrocarbons)?
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Complete combustion (excess O2O_2) gives carbon dioxide and water. The general equation for any CxHyC_xH_y:
What are substitution reactions of alkanes?
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Alkanes are unreactive towards most reagents at room temperature. With halogens (chlorine or bromine) in UV light, they undergo free radical substitution:
What are addition reactions of alkenes?
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Addition reactions break the weaker π\pi bond and add two new groups across the former double bond, leaving a saturated product.
What are reactions of alkynes?
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Alkynes undergo combustion and addition like alkenes, but each π\pi bond can be added across in turn. So ethyne plus excess bromine gives 1,1,2,2-tetrabromoethane:
What is the bromine water test?
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To distinguish a saturated hydrocarbon (alkane) from an unsaturated one (alkene or alkyne), add a few drops of bromine water and shake.
What is markovnikov direction wrong?
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The H adds to the carbon with more Hs already. Think "the rich get richer" for H atoms.
What are soot from incomplete combustion of alkanes?
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Alkanes generally burn cleanly; alkenes and alkynes are sootier. If asked to compare flames, mention the C:H ratio.
What is q1?
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State the general molecular formula for an alkane, an alkene and an alkyne, and give one observation that distinguishes an alkene from an alkane chemically. [3 marks]
What is q2?
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Write a balanced equation for the complete combustion of octane (C8H18C_8H_{18}) and calculate the volume of CO2CO_2 at 25 degrees C and 100 kPa produced from 5.00 g of octane (molar volume 24.79 L mol−1^{-1}). [3 marks]
What is q3?
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But-1-ene reacts with HBr to give a major and minor product. (a) State Markovnikov's rule. (b) Identify the major product.

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