Sodium Carbonate - Definition, Formula and Structure, Synthesis, Physical and Chemical Properties and Uses

You must have seen those eye-candy advertisements where little kids dirtying their clothes are seen being happily embraced by their mothers, stating that they have the best Brand of ‘washing powder’ and hence all dirt would vanish in no time!

Have you wondered what goes into making this special kind of ‘washing powder’? It is Sodium Carbonate, also known as washing soda, which forms the key ingredient of all such detergents. 

Hence it becomes quite obvious for us to know the chemistry of this compound and wash off all the hazes related to it.

TABLE OF CONTENTS

• What is Sodium Carbonate?
• Formula and Structure of Sodium Carbonate
• Synthesis of Sodium Carbonate
• Physical Properties of Sodium Carbonate
• Chemical Properties of Sodium Carbonate
• Use of Sodium Carbonate
• Frequently Asked Questions-FAQs

What is Sodium Carbonate?

Sodium carbonate is an inorganic compound with formula . Sodium carbonate is also commonly known as Soda ash. It is water-soluble and is known to form an alkaline solution in water. Its crystalline hydrated form is called washing soda which has the formula . Soda ash is extracted from trona, a non-marine evaporite mineral ore. Trona is a double salt containing sodium carbonate and sodium bicarbonate formed as a result of the series of evaporation processes taking place at lakes.

Sodium carbonate is of great advantage over sodium hydroxide, that it is no-corrosive and is, therefore, safer to handle.

Formula and Structure of Sodium Carbonate

Sodium carbonate () is known to be a disodium salt of carbonic acid ). In its pure form, soda ash exists as a white powder and is known to be odourless. Sodium carbonate is water-soluble and forms an alkaline solution as it is composed of salt of a strong base and weak acid.

It is composed of an ionic bond between two sodium ions and a polyatomic carbonate ion ().

Synthesis of Sodium Carbonate (

Sodium carbonate, a carbonate of an alkali metal i.e., sodium, is exclusively produced by Solvay’s process. We shall understand the various steps involved here. 

Step 1: In Solvay’s process, a saturated brine solution is made by evaporating sodium chloride sourced from inland or sea, and is then filtered and passed through an ammonia tower. The ammonia gas is absorbed in the concentrated brine. Next, is then bubbled through the ammoniated brine solution.

The resultant solution of ammoniated brine is filtered to remove and impurities, as they are insoluble carbonates.

Step 2: Formation of insoluble (in carbonation tower)

Ammonium carbonate which is formed in the first step is concentrated with and to form ammonium bicarbonate . This is an exothermic reaction.

(s)

Sodium hydrogen carbonate crystals separate here, as it is insoluble in cold brine solution because of the common ion effect. It is separated by filtration, and the filtrate is used for recovering and .

Step 3 : Next, calcination is done to get sodium carbonate at .

.

Step 4 : In this process, is recovered in the recovery tower, where some of the ammonium bicarbonate left decomposes and when the solution containing is treated with ,is a by-product.

Step 5 : Solvay thought of even preparing as a product with the following steps involved.

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Physical properties of Sodium Carbonate 

• It is a crystalline solid which is white in colour. 
• It exists as a monohydrated salt (), anhydrous salt (), heptahydrous salt () and decahydrate salt ().
• Sodium carbonate is alkaline in nature.
• It has a melting point of 851°C and boiling point of 1600 °C
• Its molar mass is 105.988
• Its density is 2.54 in an anhydrous state.
• Soda ash is highly soluble in water. 

Chemical properties of Sodium Carbonate 

• Sodium carbonate in an anhydrous state (soda ash), is stable towards heat and melts without decomposition at 851 °C.
• Decahydrate sodium carbonate when heated at 100 °C and above 100 °C forms sodium carbonate monohydrate and anhydrous sodium carbonate respectively. 

• Aqueous solutions of sodium carbonate are mildly alkaline due to hydrolysis which releases ions.

• Aqueous solutions of sodium carbonate absorb carbon dioxide from the air forming sodium hydrogen carbonate.

•  Sodium carbonate reacts with weak acids, such as lime juice liberating carbon dioxide.

Uses of Sodium Carbonate 

• It is used in water softening, laundering, and cleaning in household and industrial sectors.
• It is used in the manufacturing of glass (sodium silicate), soap, borax, and caustic soda.
• It is used in paper, paints, and textile, soap, detergent industries.
• It is an important laboratory reagent for various analytical procedures.
• It is used as a modifier of values.

Practice Problems

Q.1. Why Solvay’s process cannot be used for manufacturing ?

Answer: Solvay process cannot be extended to manufacture , because is too soluble to be precipitated by the addition of to a saturated solution of potassium chloride.

Q.2. Anhydrous sodium carbonate is commonly known as?

1. Soda Ash
2. Soda lime
3. Slaked Lime
4. Sodium hydrogen carbonate

Answer: (A)

Solution:

Anhydrous sodium carbonate i.e., is known as soda ash. Soda lime is a mixture of , i.e. sodium hydroxide and calcium oxide. Slaked lime is and sodium hydrogen carbonate is . 

Q.3. What will be the chemical formula for washing soda?

Answer: (C)

Solution: 

Washing soda is decahydrate of sodium carbonate. Hence the formula is . 

Q.4. Brine, used in Solvay’s process is a saturated solution of :

Answer: (A)

Solution: 

Brine is a saturated solution of . 

Frequently Asked Questions-FAQs

Q.1. Sodium carbonate is acid or base?

Answer: Sodium carbonate is basic in nature. It is a salt obtained from a weak acid and strong base like sodium hydroxide . Hence upon hydrolysis, gives hydroxide ions. Therefore it is a basic salt.

Q.2. What are the possible health hazards related to sodium carbonate?

Answer: On accidental exposure and inhalation, it can cause severe irritation in the respiratory tract, cause shortness of breath, and pulmonary edema. Eye contact can cause corneal damage. Hence, it should be handled carefully.

Q.3. Are detergents made from sodium carbonate environmentally friendly?

Answer: Since is naturally occurring in soil and water so it is not expected to have any negative impacts on the environment or soil. But detergents with other organic compounds and long-chain branched hydrocarbons along with inorganic sodium salts make a strongly alkaline substance which is not easily biodegradable in nature. So, detergents are not environmentally friendly.

Q.4. What is the major difference between sodium carbonate and sodium bicarbonate?

Answer: Sodium carbonate is a strongly basic salt whereas sodium bicarbonate is a weaker base and is a monoacidic base. Also, sodium carbonate is used as washing soda and sodium bicarbonate is used as baking soda in edible products like cake, dhokla etc.

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