Carbon and its Compounds · Lesson 11 of 13
Properties Of Ethanoic Acid
“Ethanoic acid makes esters, salts and carbon dioxide while quietly powering vinegar chemistry.”
• Describe the physical and acidic properties of ethanoic acid. • Explain vinegar and glacial acetic acid. • Explain esterification between ethanoic acid and ethanol. • Explain saponification and the products formed. • Write reactions of ethanoic acid with a base, carbonate and hydrogencarbonate.
Ethanoic acid, commonly called acetic acid, is the second commercially important carbon compound studied in detail. Its carboxyl group gives it acidic properties and allows it to undergo reactions characteristic of carboxylic acids.
Ethanoic acid is a carboxylic acid. A dilute aqueous solution containing a small percentage of acetic acid is called vinegar and is widely used as a food preservative, especially in pickles.
Vinegar is a dilute aqueous solution of acetic acid commonly used as a food preservative.
Glacial Acetic Acid
Pure ethanoic acid has a melting point close to ordinary winter temperatures in cold climates and can freeze there. This behaviour led to the name glacial acetic acid.
Ethanoic Acid Is A Weak Acid
Ethanoic acid shows acidic behaviour, but unlike strong mineral acids such as hydrochloric acid, carboxylic acids are weak acids. A universal indicator can therefore show a difference in acid strength even when both solutions turn suitable litmus paper toward the acidic colour.
Esterification Reaction
Esterification is the reaction of a carboxylic acid with an alcohol to form an ester and water, usually in the presence of an acid catalyst.
Ethanoic acid reacts with ethanol in the presence of an acid catalyst to form an ester. Esters are commonly sweet-smelling substances and are used in perfumes and flavouring agents.
Saponification
Saponification is the alkaline breakdown of an ester to form an alcohol and the sodium or potassium salt of a carboxylic acid.
The term is important because soap preparation involves sodium or potassium salts of long-chain carboxylic acids.
Reaction With A Base
Like other acids, ethanoic acid reacts with sodium hydroxide to form a salt and water. The salt is sodium ethanoate, also commonly called sodium acetate.
Reaction With Carbonates And Hydrogencarbonates
Ethanoic acid reacts with sodium carbonate and sodium hydrogencarbonate to produce sodium ethanoate, carbon dioxide and water. The evolved carbon dioxide can be identified by passing it through lime water.
How To Distinguish Ethanol And Ethanoic Acid
Ethanoic acid shows acidic behaviour with indicators and reacts with carbonates or hydrogencarbonates to release carbon dioxide. Ethanol does not show the same acidic indicator behaviour and does not produce carbon dioxide with these salts under the same comparison.
Problem
How can the gas from ethanoic acid reacting with sodium carbonate be identified?
- 1.The reaction produces a gas along with sodium ethanoate and water.
- 2.Pass the gas through freshly prepared lime water.
- 3.Carbon dioxide turns lime water milky because calcium carbonate forms.
- 4.This confirms that the evolved gas is carbon dioxide.
Quiz
What is the common name of ethanoic acid?
What is formed when ethanoic acid reacts with ethanol in the presence of acid catalyst?
What is saponification?
What gas forms when ethanoic acid reacts with sodium hydrogencarbonate?
Why is ethanoic acid called a weak acid?
Practice Problems
- Explain the terms vinegar and glacial acetic acid.
- Compare ethanoic acid with hydrochloric acid using acid strength and indicator behaviour.
- Write the esterification reaction between ethanoic acid and ethanol and explain the role of the acid catalyst.
- Write the saponification reaction and identify the alcohol and salt formed.
- Write the reactions of ethanoic acid with sodium hydroxide, sodium carbonate and sodium hydrogencarbonate.
- Explain how you could experimentally distinguish ethanol from ethanoic acid.
- Explain how carbon dioxide produced from ethanoic acid and carbonate can be confirmed.
Key Takeaways
• Ethanoic acid is acetic acid and belongs to the carboxylic acid family. • Vinegar is dilute acetic acid in water, while pure ethanoic acid can be called glacial acetic acid. • Ethanoic acid and ethanol form an ester and water during esterification. • Saponification breaks an ester with alkali to form an alcohol and a carboxylate salt. • Ethanoic acid reacts with bases, carbonates and hydrogencarbonates in characteristic acid reactions.