Baking Soda Washing Soda Plaster of Paris - Preparation, Formula, Uses, FAQs

Preparation of Baking Soda

Solvay Process

Baking soda is synthesized through Solvay’s process. Solvay’s process involves the reaction of Sodium Chloride, ammonia as well as carbon dioxide in water. The carbon dioxide involved is produced through Calcium Carbonate and the calcium oxide left is used in recovering ammonia from ammonium chloride. Finally, sodium bicarbonate is produced as one of the end products.

Reaction of Ammonia and Carbon Dioxide:
A concentrated solution of sodium chloride (brine) is saturated with ammonia gas, and then carbon dioxide is passed through it.

$\mathrm{NaCl}+\mathrm{NH}_3+\mathrm{CO}_2+\mathrm{H}_2 \mathrm{O} \rightarrow \mathrm{NaHCO}_3+\mathrm{NH}_4 \mathrm{Cl}$

Filtration:
The precipitated sodium hydrogen carbonate is filtered out from the solution.
Drying and Heating:
The filtered $\mathrm{NaHCO}_3$ is washed, dried, and then heated gently to remove any moisture.
(On strong heating, it decomposes to form sodium carbonate, $\mathrm{CO}_2$, and $\mathrm{H}_2 \mathrm{O}$.)

Uses of Baking Soda

• It is used as an ingredient in the manufacturing of antacids
• It is used in making soft and fluffy bread and cakes due to the production of carbon dioxide when it is heated or mixed in water.
• It is used for making soda-acid fire extinguishers.

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Washing Soda

The powder in Washing Soda is whitish and odourless. Its chemical formula is $\mathrm{Na}_2 \mathrm{CO}_3$ and it is commonly called sodium carbonate. This substance is hygroscopic, which means that it absorbs moisture from the air. Water forms a strongly Alkaline solution at low concentrations, which is soluble in water. Washing Soda's chemical name is sodium carbonate and the chemical formula of washing soda/chemical formula of Washing Soda is $\mathrm{Na}_2 \mathrm{CO}_3$.

Solvay synthesizes Washing Soda through a process that depends on phosphoric acid. Salvay’s process uses sodium chloride, ammonia, and carbon dioxide as catalysts.

Calcium carbonate generates carbon dioxide, and the leftover calcium oxide is used to recover ammonia from ammonium chloride. A sodium bicarbonate solution is first obtained, which is then converted to sodium carbonate by heating. Lastly, Washing Soda is produced by recrystallizing sodium carbonate.

Preparation Washing Soda

The first step is to produce sodium bicarbonate, which is then converted to sodium carbonate. Last but not least, Washing Soda is made from sodium carbonate recrystallize.

The Solvay manufacturing process is used to make washing soda. It is manufactured via a reaction between sodium chloride, ammonia, and carbon dioxide in water. In this process, carbon dioxide is formed by manufacturing calcium carbonate and the calcium oxide left after is used to recover ammonia from ammonium chloride.

$\mathrm{NaCl}+\mathrm{NH}_3+\mathrm{CO}_2+\mathrm{H}_2 \mathrm{O} \rightarrow \mathrm{NaHCO}_3+\mathrm{NH}_4 \mathrm{Cl}$

$2 \mathrm{NaHCO}_3 \rightarrow \mathrm{Na}_2 \mathrm{CO}_3+\mathrm{H}_2 \mathrm{O}+\mathrm{CO}_2$

$\mathrm{Na}_2 \mathrm{CO}_3+10 \mathrm{H}_2 \mathrm{O} \rightarrow \mathrm{Na}_2 \mathrm{CO}_3 \cdot 10 \mathrm{H}_2 \mathrm{O}$

Uses of Washing Soda

1.As a Cleaning Agent:

• It is used for removing dirt and stains from clothes and household articles.

• It helps soften hard water, allowing soaps and detergents to lather more effectively.

2. In the Manufacture of Glass, Soap, and Paper:

• Washing soda is an important raw material in the glass, soap, and paper industries.

3. In the Preparation of Other Chemicals:

• It is used in the manufacture of borax, caustic soda (NaOH), and other sodium compounds.

4. For Removing Permanent Hardness of Water:

• It reacts with calcium and magnesium salts in hard water to form insoluble carbonates, which makes the water soft.

5. As a Laboratory Reagent:

• Used in laboratories for various chemical reactions and neutralizations.

6. In Fire Extinguishers:

Washing soda is used in some dry chemical fire extinguishers.

Plaster of Paris

This finely powdered chemical compound hardens when exposed to moisture and allowed to dry. It has the chemical formula $\mathrm{CaSO}_4 .1 / 2 \mathrm{H}_2 \mathrm{O}$ and is sometimes referred to as Calcium Sulphate hemihydrate.

Plaster of Paris is a fine white powder consisting of a chemical compound that hardens after exposure to moisture in the air. It has the chemical formula $\mathrm{CaSO}_4 .1 / 2 \mathrm{H}_2 \mathrm{O}$ and is sometimes referred to as calcium sulphate hemihydrate. In the manufacturing process, gypsum$\left(\mathrm{CaSO}_4 \cdot 2 \mathrm{H}_2 \mathrm{O}\right)$ is used to make Plaster of Paris.

Gypsum becomes calcium sulphate (Plaster of Paris) after it is heated to 373 K, destroying its water molecules.

$\mathrm{CaSO}_4 \cdot 2 \mathrm{H}_2 \mathrm{O} \rightarrow \mathrm{CaSO}_4 \cdot 1 / 2 \mathrm{H}_2 \mathrm{O}+3 / 2 \mathrm{H}_2 \mathrm{O}$

Preparation of Plaster of Paris

Gypsum $\left(\mathrm{CaSO}_4 \cdot 2 \mathrm{H}_2 \mathrm{O}\right)$ is the basis of the Plaster of Paris. During heating at 373 K, gypsum loses its water molecules and forms calcium sulphate (Plaster of Paris).

$\mathrm{CaSO}_4 \cdot 2 \mathrm{H}_2 \mathrm{O} \rightarrow \mathrm{CaSO}_4 \cdot 1 / 2 \mathrm{H}_2 \mathrm{O}+3 / 2 \mathrm{H}_2 \mathrm{O}$

Uses of Plaster of Paris

1. In the Medical Field:

• It is used for making casts and bandages to immobilize broken bones while they heal.

2. In Construction:

• Used for coating walls and ceilings to give them a smooth finish.

• It is also used in decorative work, such as mouldings, cornices, and false ceilings.

3. In Art and Craft:

• Artists use it for making statues, models, and decorative items because it sets quickly and can be easily shaped.

4. In Making Moulds and Casts:

• Used to prepare moulds for pottery, ceramics, and metal castings.

5. For Making Chalks and Blackboards:

• Used in the manufacture of chalk sticks and blackboard chalks.

6. For Sealing and Repairs:

• It is used for filling cracks and holes in walls and ceilings as it sets into a hard, smooth mass when mixed with water.

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Some Solved Examples

Question 1: When CO₂ gas is passed through Ca(OH) ₂ solution, it leads to the formation of:

1) CaO

2) (correct) CaCO₃

3) Both a and b

4) None of these

Solution:

As we learn
Action of $\mathrm{CO}_2$ on limewater -
Turns milky due to the formation of calcium carbonate
- wherein

$\mathrm{Ca}(\mathrm{OH})_2+\mathrm{CO}_2 \rightarrow \mathrm{CaCO}_3+\mathrm{H}_2 \mathrm{O}$

Hence, the answer is option (2).

Question 2: Which of the following options is true regarding the use of plaster of Paris?

1) It can be used in the building industry

2) Used in dentistry

3) Can be used for immobility of the area of fractured bone

4) (correct) All of these

Solution :

As we learn

Uses of Plaster of Paris -

i) In the building industry

ii) Plasters for immobilising the area of bone fracture or sprain

iii) In dentistry

iv) in ornamental work

v) for making casts of statues and busts

Hence, the answer is option (4).

Question 3: Setting down of cement can be prevented by:

1) Quartz

2) Quick lime

3) Plaster of Paris

4) (correct) Gypsum

Solution:

As we have learnt in the setting of Cement,

Gypsum in cement slows down the setting.

Hence, the answer is option (4).

Question 4: The number of water molecules in gypsum, dead burnt plaster, and Plaster of Paris, respectively, is:
1) (correct) 2,0 and 0.5
2) 0.5, 0, and 2
3) 2, 0, and 1
4) 5,0, and 0.5

Solution :

As we have learnt,
Plaster of Paris $\left(\mathrm{CaSO}_4 \cdot \frac{1}{2} \mathrm{H}_2 \mathrm{O}\right)$ is obtained by heating Gypsum $\left(\mathrm{CaSO}_4 \cdot 2 \mathrm{H}_2 \mathrm{O}\right)$ to 393 K .
On heating above 393 K, no water of crystallisation is left behind, and Dead burnt plaster is obtained.
The reaction is given as

$$
\underset{\text { (Gypsum) }}{\mathrm{CaSO}_4} \cdot 2 \mathrm{H}_2 \mathrm{O} \xrightarrow[\text { (393K) }]{\Delta} \underset{\text { (Plaster of Paris) }}{\mathrm{CaSO}_4} \cdot \frac{1}{2} \mathrm{H}_2 \mathrm{O} \xrightarrow[\text { (T>393K) }]{\Delta} \underset{\text { (Dead burnt plaster) }}{\mathrm{CaSO}_4}
$$

Hence, the answer is option (1).

Practice more questions with the link given below