Ever wondered why some alcohols burn cleaner than petrol or...
Chemistry66 views·Updated 27 Jul 2026·3 pagesUnderstanding Alcohols: Reactions and Properties
Scarlett Edwardes@scarlett_1917
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1
of 3
Alcohol Basics and Combustion
Alcohols contain the hydroxyl group and can be classified as primary, secondary, or tertiary based on how many carbon atoms are attached to the carbon bearing the OH group. This classification massively affects how they react!
When alcohols burn in air, they produce a clean, pale blue flame and undergo complete combustion to form water and carbon dioxide. This makes them brilliant fuels because they help reduce our carbon footprint - especially ethanol made from fermented sugar.
Substitution reactions happen when alcohols react with halogen-containing substances. The carbon attached to OH becomes slightly positive , making it attractive to nucleophiles. For making chloroalkanes, you can react alcohols with phosphorus pentachloride (PCl₅) or hydrochloric acid - tertiary alcohols react fastest, primary alcohols slowest.
Quick Tip: Remember the reactivity order for haloalkanes: iodoethane (most reactive) → bromoethane → chloroethane (least reactive). It's all about bond strength!
2
of 3
Making Haloalkanes and Dehydration
Creating bromoalkanes involves substitution reactions where the hydroxyl group gets replaced by a bromide ion. You'll need an acid catalyst like 50% concentrated sulphuric acid to make this happen effectively.
For iodoalkanes, chemists use phosphorus triiodide (PI₃), usually made during the reaction itself by mixing the alcohol with red phosphorus and iodine under reflux conditions. The equation is: 3ROH + PI₃ → 3RI + H₃PO₃.
Dehydration reactions are elimination reactions that need an acid catalyst and heat. A water molecule forms from the OH group plus another hydrogen atom, and which hydrogen gets removed affects your final product - you'll end up with alkenes. The position of the double bond depends on which hydrogen was eliminated.
Test Alert: If you see damp white gas forming, test it with litmus paper - it's probably HCl gas, which will turn the paper red!
3
of 3
Oxidation Reactions and Testing
Oxidation of alcohols follows predictable patterns that you absolutely need to know. Primary alcohols oxidise to aldehydes, then to carboxylic acids. Secondary alcohols form ketones. Tertiary alcohols? They don't oxidise at all under normal conditions.
The key is controlling your conditions: use distillation to collect aldehydes before they oxidise further, or use reflux when you want carboxylic acids. Your go-to oxidising agent is usually potassium dichromate with sulphuric acid.
Chemical tests are crucial for identification. When acidified potassium dichromate oxidises alcohols, you'll see the orange dichromate turn green. Fehling's solution is brilliant for distinguishing aldehydes from ketones - it goes from blue to brick red with aldehydes when heated, but stays blue with ketones.
Memory Trick: "Reflux for carboxylic, distillation for aldehyde" - because you can collect the aldehyde before it becomes a carboxylic acid!
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Chemistry66 views·Updated 27 Jul 2026·3 pagesUnderstanding Alcohols: Reactions and Properties
Scarlett Edwardes@scarlett_1917
Ever wondered why some alcohols burn cleaner than petrol or how they transform into completely different compounds? Alcohols are versatile organic molecules that can undergo fascinating chemical reactions, from being oxidised into aldehydes and acids to being converted into halogen-containing...
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Alcohol Basics and Combustion
Alcohols contain the hydroxyl group and can be classified as primary, secondary, or tertiary based on how many carbon atoms are attached to the carbon bearing the OH group. This classification massively affects how they react!
When alcohols burn in air, they produce a clean, pale blue flame and undergo complete combustion to form water and carbon dioxide. This makes them brilliant fuels because they help reduce our carbon footprint - especially ethanol made from fermented sugar.
Substitution reactions happen when alcohols react with halogen-containing substances. The carbon attached to OH becomes slightly positive , making it attractive to nucleophiles. For making chloroalkanes, you can react alcohols with phosphorus pentachloride (PCl₅) or hydrochloric acid - tertiary alcohols react fastest, primary alcohols slowest.
Quick Tip: Remember the reactivity order for haloalkanes: iodoethane (most reactive) → bromoethane → chloroethane (least reactive). It's all about bond strength!
2
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Making Haloalkanes and Dehydration
Creating bromoalkanes involves substitution reactions where the hydroxyl group gets replaced by a bromide ion. You'll need an acid catalyst like 50% concentrated sulphuric acid to make this happen effectively.
For iodoalkanes, chemists use phosphorus triiodide (PI₃), usually made during the reaction itself by mixing the alcohol with red phosphorus and iodine under reflux conditions. The equation is: 3ROH + PI₃ → 3RI + H₃PO₃.
Dehydration reactions are elimination reactions that need an acid catalyst and heat. A water molecule forms from the OH group plus another hydrogen atom, and which hydrogen gets removed affects your final product - you'll end up with alkenes. The position of the double bond depends on which hydrogen was eliminated.
Test Alert: If you see damp white gas forming, test it with litmus paper - it's probably HCl gas, which will turn the paper red!
3
of 3Sign up to see the content. It's free!
- Access to all documents
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Oxidation Reactions and Testing
Oxidation of alcohols follows predictable patterns that you absolutely need to know. Primary alcohols oxidise to aldehydes, then to carboxylic acids. Secondary alcohols form ketones. Tertiary alcohols? They don't oxidise at all under normal conditions.
The key is controlling your conditions: use distillation to collect aldehydes before they oxidise further, or use reflux when you want carboxylic acids. Your go-to oxidising agent is usually potassium dichromate with sulphuric acid.
Chemical tests are crucial for identification. When acidified potassium dichromate oxidises alcohols, you'll see the orange dichromate turn green. Fehling's solution is brilliant for distinguishing aldehydes from ketones - it goes from blue to brick red with aldehydes when heated, but stays blue with ketones.
Memory Trick: "Reflux for carboxylic, distillation for aldehyde" - because you can collect the aldehyde before it becomes a carboxylic acid!
We thought you’d never ask...
Our AI Companion is a student-focused AI tool that offers more than just answers. Built on millions of Knowunity resources, it provides relevant information, personalised study plans, quizzes, and content directly in the chat, adapting to your individual learning journey.
You can download the app from Google Play Store and Apple App Store.
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Similar content
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