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Washing Soda

Washing Soda is an alkaline compound, which is highly alkaline or basic in nature with a pH value of 11. Its chemical formula is Na₂CO₃.10H2O and is chemical name is sodium carbonate decahydrate. It is also known as soda ash as it can be obtained from the ashes of burned plants. Washing soda is a sodium salt of carbonic acid and is made of two sodium ions and one carbonate ion. Its molar mass is molar mass of Na₂CO₃ is 106 g/mol.

Washing soda is known for its ability to remove stubborn stains from clothes. It is a powerful water softener. It softens the water by binding to the substances that make water hard and allows the clothes to absorb detergent properly for better cleaning. So, it is found as the main component of detergents.

Properties of Washing Soda

• It occurs as an odourless white crystalline solid.
• It has a high alkaline or basic nature as its pH value is 11.
• Its melting point is 851 degrees centigrade.
• When heated, it loses water and thus forms an anhydrous salt.
• It is a hygroscopic solid. It dissolves in water to form bit acidic carbonic acid and sodium hydroxide (strong base).
• Its aqueous solution is a strong base, which reacts quickly with many acids.

Preparation of Sodium Carbonate I Solvay process

The preparation of washing soda involves Solvay process that includes the following steps;

Step 1: Formation and Purification of Brine and formation of ammoniated brine solution

In this step, first, the concentrated solution of sodium chloride is prepared through evaporation. This solution of NaCl is known as brine. The impurities present in the brine are removed by precipitation. Then the concentrated brine solution is filtered and ammonia is mixed with it in the ammonia tower that results in the formation of ammoniated brine solution.

Step 2: Formation of sodium hydrogen carbonate

In this step, carbon dioxide is passed through the ammoniated brine solution. A chemical reaction occurs that gives ammonium chloride and sodium bicarbonate as products. This process occurs in a carbonated tower. The chemical reaction that takes place is shown below;

NH3 (aq) + CO2 (g) + NaCl (aq) + H₂O → NaHCO₃ (s) + NH₄Cl (aq)

Step 3: Formation of Sodium Carbonate

The sodium bicarbonate formed in the previous step is collected from the tower. It is then heated at a temperature of 300 degrees centigrade that leads to the formation of anhydrous sodium carbonate as shown in the below chemical reaction;

2NaHCO₃ → Na₂CO₃ + CO₂ + H₂O

Step 4: Formation of Sodium carbonate decahydrate

10 water molecules are to sodium carbonate which forms hydrated sodium carbonate, which is called Washing Soda. The reaction is shown below

Na₂CO₃ + 10 H₂O —> Na₂CO₃.10H₂O

Step 4: Recovery of ammonia

Ammonia used in this process can be recovered from ammonium chloride (NH₄Cl) formed in the second step. It is obtained by the reaction of a solution of ammonium chloride (NH4Cl) with Ca (OH)₂. The chemical reaction is shown below. This recovered ammonia is reused in the Solvay process.

2NH₄Cl + Ca (OH)₂ → 2NH₃ + CaCl₂ + H₂O

Uses of Washing Soda

• It has the ability to remove a wide range of stains. So it is found as a major component of detergents or can be used as a standalone cleaning agent.
• It is used in the textile industry by textile artists to stick dyes to fabrics. It is particularly used this way for the natural dyes obtained from plants.
• It can be used to remove oily build-up from pans, oven racks, pots, etc., and to remove stains of tea and coffee from plastic containers and ceramics.
• It can also unclog drains. For this, you have to pour around one cup of it into the drain followed by 2 cups of boiling water. Leave it for around 30 minutes then flush the drain.
• It also works well to clean outdoor furniture such as tables, chairs, decks placed in the garden.
• A solution made by mixing half a cup and 2 gallons of water can be used as a spray against aphids, flies, and to prevent black spots on roses.

Note: Washing soda may be dangerous in large quantities, so make sure it is away from the reach of children and pets. Since it can cause skin irritation, you should wear gloves while using washing soda.

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