Saponification
An ester treated with an alkali.
Undoing an ester
An ester is made from an acid and an alcohol. Now sodium hydroxide, an alkali, is added to an ester.
What do you expect to be formed?
What this lesson covers
The idea
An ester treated with sodium hydroxide, an alkali, is converted back to the alcohol and the sodium salt of the carboxylic acid; this reaction is saponification, as it is used to prepare soap.
Undoing an ester
An ester is made from an acid and an alcohol. Now sodium hydroxide, an alkali, is added to an ester.
What do you expect to be formed?
- The alcohol and the sodium salt of the carboxylic acid
- Only the carboxylic acid
- Carbon dioxide and water only
Ester with an alkali
Press Next step. A teacher does this in the lab.
The reverse of making an ester
Sodium hydroxide turns the ester back into the alcohol. The acid part appears as its sodium salt. This is how soap is made.
An ester treated with sodium hydroxide, an alkali, is converted back to the alcohol and the sodium salt of the carboxylic acid. This reaction is saponification, as it is used to prepare soap.
Notes
An ester treated with sodium hydroxide, an alkali, is converted back to the alcohol and the sodium salt of the carboxylic acid. This is saponification, as it is used to prepare soap.
Check yourself
What is added to an ester in saponification?
What are formed when an ester is treated with sodium hydroxide?
Why is the reaction called saponification?
Soaps are sodium or potassium salts of which kind of acids?
- Concentrated sulphuric acid. Concentrated sulphuric acid is the dehydrating agent used on ethanol.
- Hydrogen with a nickel catalyst. Hydrogen with nickel is used to add hydrogen to unsaturated hydrocarbons.
- Sodium hydroxide, an alkali — correct. Yes!
- The alcohol and the sodium salt of the carboxylic acid — correct. Yes!
- The carboxylic acid and the alcohol. The carboxylic acid is not formed itself. Its sodium salt is formed along with the alcohol.
- An ester and water. An ester and water are formed when an acid reacts with an alcohol, which is the opposite change.
- It produces a gas that cleans. The name comes from its use in the preparation of soap.
- It is used in the preparation of soap — correct. Yes!
- It needs sunlight. The name comes from its use in the preparation of soap, not from sunlight.
- Mineral acids such as HCl. Soaps are salts of long-chain carboxylic acids.
- Short unsaturated hydrocarbons. Hydrocarbons are not acids. Soaps are salts of long-chain carboxylic acids.
- Long-chain carboxylic acids — correct. Yes!