Baking Soda and Washing Soda

Introduction: 

By now we know that the combination of acid and base forms salts. Common salt (NaCl) can be formed by combining hydrochloric acid and sodium hydroxide solution. This common salt is very important for our body to the maintain balance of fluids and keep nerves and muscles running smoothly. The salt thus obtained is an important raw material for the substances we use daily, such as washing soda, baking soda, bleaching powder, and many more. 

Washing soda is a key component in all laundry soaps and detergents, not only these but many household products. Washing soda is also used in the paper and wool industries, but the major demand comes from the glass industry. The world demand for sodium carbonate stands at over 50 million tons per year. 

It’s such huge demand to fulfil this, but for economic reasons, most of it is now manufactured by an industrial process known as the Solvay process.  

Baking soda is also another important substance used in food industries. Baking soda is also used as a mild antacid, even its main component in fire extinguishers. 

Let us learn more about these substances like washing soda and baking soda obtained from common salt. 

Sodium Carbonate (Na₂CO3) 

Sodium carbonate is also termed as washing soda, and it is a sodium salt of carbonic acid.  

The molecular formula of sodium carbonate is Na₂CO_3. 

It is commonly mentioned as soda ash because it was originally obtained from burned seaweed’s ashes. 

Preparation of Sodium Carbonate 

Solvay Process: 

For over a decade, sodium carbonate has been manufactured mainly by a method known as the Solvay process. This process is also called the ammonia-soda process. 

The starting materials used in this process are Brine, calcium carbonate, ammonia, and water.  

Brine: Sodium chloride provides sodium ions to make the sodium carbonate. It can be easily obtained from ocean and seawater by evaporation. 

Calcium carbonate: It is also known as Limestone. Calcium carbonate provides carbonate ions in the formation of sodium carbonate. It is readily available from mining. 

Ammonia: It can be obtained technologically by Haber’s process. Ammonia is an expensive substance, but it is recycled in this process. 

Obtaining washing soda by Solvay process involves many chemical reactions; however, main parts of this process include: 

1. Purification of Brine 

2. Formation of Sodium Hydrogen Carbonate and Sodium Carbonate 

3. Recovery of Ammonia 

1. Purification of Brine:  

First, the Brine is subjected to evaporation to increase the concentration of NaCl. Precipitation of Brine is carried out to get impurity-free (Mg, Fe, Ca Salts) NaCl solution. 

Saturation of Brine with ammonia and CO₂: Finally, this saturated brine solution passes through the ammonia tower to get aqueous sodium chloride. (Ammonia was also obtained during the process). The process is a very exothermic reaction. So, energy is released as heat. The ammonia tower cooled. 

Ammoniated brine is filtered to remove calcium and magnesium impurities as insoluble carbonates.  

Step-2: Formation of Sodium Hydrogen Carbonate (In carbonation tower) 

The purified brine (NaCl) solution is first saturated with ammonia and then carbonated with CO₂ forming NaHCO_3. 

NaHCO₃ is insoluble in cold brine solution because of the common ion effect. It is separated by filtration, and the filtered is used for recovering NH₃ & CO₂. 

The above reaction is a precipitation reaction in which the sodium hydrogen carbonates come as a solid white precipitate. 

The key reaction in Solvay synthesis is,  

NaCl + NH₃ +CO₂+H₂O ® NaHCO₃(s) +  NH₄Cl 

2. Calcination to Get Sodium Carbonate 

When sodium bicarbonate is heated, it gives sodium carbonate, water vapors and CO₂ gas. 

The calcium oxide is reacted with water to produce basic calcium hydroxide.  

Step – 4 (In recovery tower): Ammonia and carbon dioxide recovery.  

The solution containing ammonium chloride is treated with Ca(OH)₂. Calcium chloride is obtained as a by-product. In this process, NH₃ is recovered, and CO₂ is recycled (for NaHCO₃ synthesis.) 

Here the ammonia is recycled, which makes the Solvay process more economical. 

The whole Solvay process can be summarized shown as 

Advantage of the Solvay process: 

1. It uses inexpensive, abundantly available raw materials NaCl brine and limestone (CaCO₃).  

2. It maximizes recycle of two major reactants, ammonia, and carbon dioxide. 

Note : It may be mentioned here that Solvay process cannot be extended to the manufacture of postassium carbonate because potassium hydrogen carbonate is too soluble to be precipitated by the addition of ammonium hydrogen carbonate to a saturated solution of potassium chloride. 

Physical Properties of Sodium Carbonate: 

1. Sodium carbonate is a white crystalline solid with a melting point of 851 °C. 

2. Sodium carbonate is soluble in water. 

Chemical Properties of Sodium Carbonate: 

1. Washing soda is a white crystalline solid, and it exists as a decahydrate, Na₂CO₃·10H₂O. 

2. Heating Effect: Anhydrous Na₂CO₃ is called soda ash, which does not decompose on heating but melts at 852 °C. 

On heating, this decahydrate loses its water of crystallisation to form monohydrate. Above 373 K, the monohydrate becomes completely anhydrous and changes to a white powder called soda ash. 

3. Reaction With Water: It is readily soluble in water. The carbonated part of sodium carbonate gets hydrolyzed by water to form an alkaline solution. 

4. Reaction with CO₂: Passing CO₂ through its aqueous solution produces sodium hydrogen carbonate. 

5. It dissolved in acid with the effervescence of CO₂ and causticized by lime to give caustic soda. 

Uses of Sodium Carbonate: 

1. Sodium carbonate is used in water softening plants, cleaning, and laundering. 

2. It is mainly used in the production of glasses. Washing soda is also used to manufacture borax, soap, and caustic soda. 

3. It is used in paper, paints, and textile industries.  

4. It is an important laboratory reagent both in qualitative and quantitative analysis.  

Sodium Hydrogen Carbonate (NaHCO₃) 

Chemical name of baking soda is sodium hydrogen carbonate or sodium bicarbonate. 

Its molecular formula is NaHCO₃. 

Preparation Of Sodium Bicarbonate 

1. By Solvay Process: It is an intermediate product of Solvay’s process. 

2. From Sodium Carbonate: 

Sodium hydrogen carbonate is made by saturating a solution of sodium carbonate with carbon dioxide. (The white crystalline powder of sodium hydrogen carbonate, which is less soluble, gets separated out.) 

Physical Properties of Sodium Bicarbonate 

1. It is a white crystalline substance. 

2. It is sparingly soluble in water. 

3. Sodium bicarbonate is non-flammable. 

Chemical Properties of Sodium Bicarbonate 

1. Water: It reacts with water to form carbonic acid and sodium hydroxide. 

2. Heating Action: On heating, it decomposes to give sodium carbonate and CO₂, which is used to detect bicarbonates. 

Uses Of Sodium Bicarbonates: 

1. It is used as ‘SODA BICARB’ to neutralize stomach acidity. 

2. It is used in fire extinguishers: It is used as one of the components along with sulfuric acid. In fire extinguishers, sodium bicarbonate and sulphuric acid are kept in different chambers. They can react with each other to give carbon dioxide. 

• Carbon dioxide so produced is thrown over the fire, which covers the fire and stops oxygen supply.  
• This fire extinguisher is also known as a soda-acid fire extinguisher. 

3. Sodium hydrogen carbonate is a mild antiseptic for skin infections. 

4. It is used as baking powder in the manufacturing of cake, making it fluffy.  

The backing powder contains  NaHCO₃ and Ca(H₂PO₄)₂. H₂O 

The CO₂ produced makes cake or bread rise. 

5. It is used in toothpaste for whitening the teeth and removing plaque. 

6. It is used as bio-pesticide. 

Summary:

• Sodium chloride (NaCI) is a very important raw material for the manufacture of many
• substances that are used in daily life, like sodium carbonate and sodium bicarbonate.
• Sodium carbonate (washing soda) is a white crystalline solid and soluble in water. Sodium carbonate is prepared commercially by using the Solvay process. The raw
• material used in this process is calcium carbonate, ammonia, sodium chloride and water.
• Na2CO3 exists as dehydrate Na2CO3-10H2O, but after heating, above 373 K becomes
• completely anhydrous and is called soda ash. It reacts with water and CO: to give carbonic acid and sodium bicarbonate.
• It is used in water softening, the textile industry, the glass industry, and cleaning. Sodium bicarbonate is another chemical that is obtained as an intermediate in the Solvay
• process.
• It is a white crystalline solid, non-flammable and sparingly soluble in water.
• When sodium bicarbonate is heated, sit gives sodium carbonate as a product.
• It is used as antacids, mild antiseptic, biofertilizer.
• NaHCO is also used in the manufacturing of cake and as a fire-extinguisher.