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Alcohols and carboxylic acids

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Explainer Video

Tutor: Alisha

Summary

Alcohols and carboxylic acids

In a nutshell

Alcohols are molecules with the functional group $-OH$ and have the suffix '-ol.' Carboxylic acids have the functional group $-COOH$ and have the suffix '-anoic acid.'

Equations

reactants		products
$sugar$	$\overset{yeast}{\rightarrow}$	$ethanol + carbon \space dioxide$
$carboxylic \space acids + metal \space carbonates$	$\rightarrow$	$salt + water + carbon \space dioxide$
$alcohol + carboxylic \space acid$	$\rightarrow$	$ester + water$

Alcohols

Alcohols have the functional group $-OH$ and the general formula $C_nH_{2n+1}OH$ . You need to know names of the first four alcohols.

Name	chemical formula
Methanol	$CH_3OH$
Ethanol	$C_2H_5OH$
Propanol	$C_3H_7OH$
Butanol	$C_4H_9OH$

1. Methanol, 2. Ethanol, 3. Propanol, 4. Butanol

Properties of alcohols

The alcohols mentioned above have similar properties.

property	explanation
Flammable	Undergo complete combustion producing carbon dioxide and water.
Water soluble	Solutions have a neutral pH.
Undergo oxidation	React with oxygen to form a carboxylic acid.
React with sodium	Alcohols react with sodium to form a salt and hydrogen.

Uses of alcohols

Use	which alcohol?	Example
Solvent	Methanol and ethanol can be used as solvents to dissolve both water soluble and non-water soluble substances.	Methanol can dissolve hydrocarbons and fats.
Fuel	All four alcohols mentioned can be used as fuels.	Ethanol is used in spirit burners.

Ethanol formation

Ethanol can be formed via fermentation to produce alcoholic beverages, in the presence of yeast. Anaerobic conditions are required, this means that fermentation must happen in the absence of oxygen. This is because the enzyme in yeast works best in anaerobic conditions. Fermentation also happens most efficiently at $37\ \degree C$ and under slightly acidic conditions.

$sugar \overset{yeast}{\rightarrow} ethanol + carbon \space dioxide$

Note: If the conditions are far from the optimum, the enzyme in yeast may denature and the reaction would occur more slowly or not at all.

Carboxylic acids

Carboxylic acids have the functional group $-COOH$ and the general formula $C_nH_{2n+1}COOH$ . Carboxylic acids are weak acids. This is because when they dissolve they form anionic ions and release a low concentration of $H^+$ ions present, forming weak acidic solutions. This is why they have a higher pH than other acids, such as hydrochloric acid.

You need to know names of the first four carboxylic acids.

name	chemical formula
Methanoic acid	$HCOOH$
Ethanoic acid	$CH_3COOH$
Propanoic acid	$C_2H_5COOH$
Butanoic acid	$C_3H_7COOH$

1. Methanoic acid, 2. Ethanoic acid, 3. Propanoic acid, 4. Butanoic acid

Reactions of carboxylic acids

Carboxylic acids react like other acids.

$carboxylic \space acids + metal \space carbonates \rightarrow salt + water + carbon \space dioxide$

Example

$ethanoic \space acid + magnesium \,carbonate \rightarrow magnesium \,ethanoate + water + carbon \,dioxide\\ \ \\CH_3COOH+MgCO_3 \rightarrow CH_3COO ^-Mg^+ + H_2O + CO_2$

Esters

Esters have the functional group $-COO$ . They are formed by reacting an alcohol and carboxylic acid together, in the presence of an acid catalyst such as concentrated sulfuric acid.

$alcohol + carboxylic \space acid \rightarrow ester + water$

Example

$methanol + ethanoic \,acid \rightarrow {methyl \,ethanoate + water} \\ \ \\ CH_3OH + CH_3COOH \rightarrow H_3COOCCH_3 + H_2O$

Learn with Basics

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