Unsaturated Hydrocarbons MCQs Quiz | Class 10
Test your understanding of Class X Science (Code 086), Unit I: Chemical Substances – Nature and Behaviour. This quiz covers Alkenes, Alkynes, double/triple bonds, and their basic properties. Click ‘Submit Quiz’ to see your score and download the PDF answer key.
Overview of Unsaturated Hydrocarbons
Unsaturated hydrocarbons are organic compounds that contain at least one carbon-carbon double bond or triple bond. Unlike saturated hydrocarbons (alkanes), they have fewer hydrogen atoms bonded to the carbon atoms than the maximum possible number. This unsaturation makes them more reactive chemically.
Key Classifications
- Alkenes: Hydrocarbons containing at least one double bond between two carbon atoms. They form a homologous series with the general formula CnH2n. The simplest alkene is Ethene (C2H4).
- Alkynes: Hydrocarbons containing at least one triple bond between two carbon atoms. They form a homologous series with the general formula CnH2n-2. The simplest alkyne is Ethyne (C2H2).
Comparison Table
| Series | Bond Type | General Formula | Suffix | Example |
|---|---|---|---|---|
| Alkane | Single (C-C) | CnH2n+2 | -ane | Ethane |
| Alkene | Double (C=C) | CnH2n | -ene | Ethene |
| Alkyne | Triple (C≡C) | CnH2n-2 | -yne | Ethyne |
Important Properties
- Combustion: They burn with a yellow, sooty flame due to incomplete combustion caused by a high percentage of carbon.
- Addition Reactions: Unsaturated hydrocarbons undergo addition reactions. For example, adding hydrogen (hydrogenation) in the presence of catalysts like Nickel or Palladium converts vegetable oils into fats.
- Test for Unsaturation: They decolorize bromine water (which is brown) and alkaline potassium permanganate solution (purple), confirming the presence of double or triple bonds.
Quick Revision List
- Minimum 2 carbon atoms are needed to form an alkene or alkyne.
- Ethene is used to ripen fruits; Ethyne is used in welding torches.
- Saturated hydrocarbons burn with a clean blue flame; Unsaturated burn with a sooty flame.
- Valency of carbon is always 4 in all these compounds.
Extra Practice Questions
- Write the electron dot structure of Ethene.
- Why do unsaturated hydrocarbons show addition reactions while saturated ones do not?
- What happens when Ethyne is burnt in air?
- Differentiate between an alkane and an alkene based on burning behavior.
- Name the catalyst used in the hydrogenation of vegetable oils.
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