Saponification

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We use soap on daily basis and now a days soap making is very common at home. People love to make soaps at home of their own choice. Being a science student, have you ever thought of which reaction is involved in soap making? If yes and didn’t get an answer yet, then in this article we are going to explain you the reactions involved in soap making. Saponification definition, saponification reaction, saponification value are some of the important topics for your CBSE Class 10 Board Exam perspective also. You will perform soap making practical as well in chemistry lab of your school in class10. 

What is Saponification? 

In the word saponification, word ‘sapo’ is actually a Latin word which means soap. In general words we can say the process of making soap is called saponification. Soaps are long chains of sodium and potassium salts of fatty acids. In terms of chemistry saponification can be define as the reaction of ester with water and base such as NaOH or KOH to give alcohol and sodium or potassium salt of the acid. The oils which go through the saponification reaction are known as saponified oils. Saponified oils are mixed with sodium hydroxide and water. 

General Saponification Reaction – 

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In words saponification reaction can be written as –

Ester + Water + Base 🡪 Soap (Sodium or Potassium Salts of fatty Acids) + Alcohol  

Or

Fat + Sodium Hydroxide SaponificationGlycerol + Soap (Crude)

In a saponification reaction, ester group reacts with water and base (mostly NaOH) and forms carboxylate ion and alcohol. Carboxylate ion changes into carboxylic acid. The saponification is named as saponification because soaps are made by hydrolysis of fats (esters) since olden times. 

Saponification Reaction (in detail)

Saponification reaction involves reaction of sodium or potassium hydroxides with triglycerides (esters) to produce glycerol (alcohol) and fatty acid salts of potassium or sodium. The fatty acid salts of potassium or sodium are known as ‘soaps’. 

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Saponification Reaction Mechanism 

Saponification reaction mechanism involves following three steps – 

Step 1. 

Nucleophilic attack by hydroxide ion – Nucleophile hydroxide ion attacks on the ester group and forms orthoester. 

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Step 2.

Removal of Leaving group i.e. alkoxide - Orthoester splits and form carboxylic acid (RCOOH) and alkoxide group (OR’). 

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Step 3.

Deprotonation – Deprotonation between carboxylic acid and alkoxide give rise to alcohol and carboxylate ions. 

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Saponification Number or What is Saponification Value?

The amount of base required to saponify 1 gram of fat under specific conditions is known as saponification value or saponification number for that particular fat. It is expressed in terms of KOH or NaOH. Its means that it is expressed in milligrams of KOH or NaOH used in the saponification. 

It can also be defined as the mass of potash in milligrams needed to neutralize the fatty acids and to saponify the esters present. 

Significance of Saponification Value 

1. It tells you about the length of carbon chain in fatty acid being used for saponification. 

2. Saponification value of those fatty acids which have very long carbon chain is generally low. 

3. Saponification value will be higher for fats containing short carbon chain. For example, saponification value for butter is 230-240 while for human fat it is 195-200. 

4. It gives an idea about average molecular weight of the fat or oil used in saponification.

Examples of Saponification Reactions – 

Triglyceride reaction with potassium hydroxide is an example of saponification reaction. 

Reaction – In words – 

Triglyceride + Potassium Hydroxide 🡪 Glycerol + Soap 

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Saponification of triglyceride is a two-step reaction – we are explaining here the two-step process by using NaOH as base. 

Step 1. It involves steam hydrolysis of triglyceride under high pressure which yields glycerol and fatty acids. 

Reaction - 

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Step 2. Fatty acids react with base and forms soap molecules. It’s a simple acid base reaction. 

Reaction - 

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Uses of Saponification 

1. It is used in the fire extinguishers. Burning oils are converted into non-combustible salts which helps in extinguishing the fire. This reaction is endothermic, so it lowers the temperature of surroundings. 

2. Oil paintings get damaged by saponification reaction. 

3. Soaps are made by saponification reaction. Soaps are very useful in many fields. They are used for cleaning, lubricating, laundry etc. 

Saponification Experiment

CBSE Class 10 Science (Chemistry) includes the experiment preparation of soap (Saponification). Practical based questions are asked in your final board examination of at least 12 marks. So, in this way it is an important experiment for you to understand. Here we are giving you procedure followed in the experiment.

Procedure of Saponification Experiment – 

  • Take about 15ml of vegetable oil in a beaker. 

  • Now add 10ml of ethanol and 20ml of 20% sodium hydroxide to vegetable oil with stirring. Don’t touch solid NaOH directly by your hands and stir the solution carefully so that it should not spill out of the beaker. 

  • Heat the mixture for 15-20 minutes until it doesn’t have two separate layers. Don’t overheat the mixture. Take care that oil doesn’t catch fire. 

  • Remove the beaker from the burner and add 15ml of saturated sodium chloride solution. 

  • Cool the mixture till it becomes solid. 

  • Now take the solid and cut it into desired shapes. 

Saponification topic is an important topic in your final board examination. So, prepare the topic strongly. Practice all the questions related to this topic. Still if you have any doubts go through study material, NCERT Solutions of Class 10, doubt sessions, online classes provided by Vadantu.