Which of the following is not correct about Baking Soda ?

1. Understanding the pH Scale and Nature of Substances (basic)

In chemistry, we determine how acidic or basic a substance is by using the pH scale. The term 'pH' originates from the German word potenz, which means 'power,' specifically referring to the power or concentration of hydrogen ions in a solution Science, Class X (NCERT 2025 ed.), Chapter 2, p. 25. This scale ranges from 0 to 14. A value of 7 is considered neutral (like pure water), while values below 7 are acidic and values above 7 are basic (or alkaline) Environment, Shankar IAS Academy (10th ed.), Environmental Pollution, p. 102. It is crucial to remember that the scale is logarithmic; this means a solution with a pH of 4 is ten times more acidic than one with a pH of 5, and a hundred times more acidic than one with a pH of 6.

The chemistry of everyday substances often involves salts, which are formed through a neutralization reaction between an acid and a base (Acid + Base → Salt + Water) Science, Class X (NCERT 2025 ed.), Chapter 2, p. 21. However, not all salts are neutral. For instance, Baking Soda (chemically known as sodium hydrogencarbonate or NaHCO₃) is a mild, non-corrosive basic salt Science, Class X (NCERT 2025 ed.), Chapter 2, p. 31. Because it is non-corrosive and has a mild alkaline nature (typically a pH around 8-9), it is safe for human consumption and household use, such as neutralizing excess acid in the stomach (acting as an antacid) or helping food cook faster.

Nature of Solution	pH Range	Ion Concentration
Acidic	0 to < 7	Higher H₃O⁺ (Hydronium) concentration
Neutral	7	Equal H₃O⁺ and OH⁻ concentration
Basic/Alkaline	> 7 to 14	Higher OH⁻ (Hydroxide) concentration

Sources: Science, Class X (NCERT 2025 ed.), Chapter 2: Acids, Bases and Salts, p.18, 21, 25, 29, 31; Environment, Shankar IAS Academy (10th ed.), Environmental Pollution, p.102

2. Classification of Salts: Acidic, Basic, and Neutral (basic)

In chemistry, a salt is not just the white powder on your dining table; it is a diverse class of ionic compounds formed when an acid reacts with a base in a neutralization reaction. While we often think of neutralization as producing something "neutral," the resulting salt can actually be acidic, basic, or neutral depending on the relative "strength" of the parents that created it.

The character of a salt depends on the degree of ionization of its parent acid and base. Strong acids (like Hydrochloric acid, HCl) release a high concentration of H⁺ ions, while weak acids (like Acetic acid, CH₃COOH) release fewer Science, Class X (NCERT 2025 ed.), Chapter 2, p.26. Similarly, strong bases produce more OH⁻ ions than weak bases. Think of it as a tug-of-war: the stronger parent dictates the nature of the child (the salt).

Parent Acid	Parent Base	Nature of Salt	pH Value
Strong	Strong	Neutral	pH = 7
Strong	Weak	Acidic	pH < 7
Weak	Strong	Basic	pH > 7

Science, Class X (NCERT 2025 ed.), Chapter 2, p.29

A classic example of a basic salt is Sodium Hydrogen Carbonate (NaHCO₃), commonly known as Baking Soda. It is formed from a strong base (Sodium Hydroxide) and a weak acid (Carbonic Acid). Because the base is stronger, the salt is mildly basic and non-corrosive, making it safe for sensitive uses like neutralizing stomach acid (as an antacid) or even faster cooking of foods like dal Science, Class X (NCERT 2025 ed.), Chapter 2, p.31.

Sources: Science, Class X (NCERT 2025 ed.), Chapter 2: Acids, Bases and Salts, p.26; Science, Class X (NCERT 2025 ed.), Chapter 2: Acids, Bases and Salts, p.29; Science, Class X (NCERT 2025 ed.), Chapter 2: Acids, Bases and Salts, p.31

3. Industrial Chemicals: The Chlor-Alkali Process (intermediate)

The Chlor-Alkali process is one of the most vital industrial reactions in modern chemistry, serving as the foundation for manufacturing everyday items from soap to PVC pipes. The process begins with brine, which is simply a concentrated aqueous solution of sodium chloride (NaCl). When electricity is passed through this solution, a decomposition reaction occurs. It is named 'Chlor-Alkali' because of the two primary chemical products generated: chlorine (chlor) and sodium hydroxide (an alkali) Science, Acids, Bases and Salts, p.30.

During electrolysis, the salt water decomposes into three distinct and valuable products. Chlorine gas (Cl₂) is released at the anode (the positive electrode), while hydrogen gas (H₂) is released at the cathode (the negative electrode). Simultaneously, sodium hydroxide (NaOH), a strong base, forms in the solution near the cathode. It is important to remember that while many bases exist, an alkali is specifically a base that dissolves in water, characterized by a soapy touch and corrosive nature Science, Acids, Bases and Salts, p.24. The chemical equation for this transformation is:
2NaCl(aq) + 2H₂O(l) → 2NaOH(aq) + Cl₂(g) + H₂(g)

The industrial significance of these products cannot be overstated. Chlorine is essential for water treatment, swimming pools, and the production of disinfectants and CFCs. Hydrogen is used largely for fuels and the production of ammonia for fertilizers. Sodium hydroxide, the alkali component, is indispensable for degreasing metals, manufacturing paper, and creating soaps and detergents. This process perfectly illustrates how a simple substance like common salt can be converted into high-value industrial chemicals through applied electricity.

Sources: Science, Acids, Bases and Salts, p.30; Science, Acids, Bases and Salts, p.24

4. Adjacent Everyday Salts: Bleaching Powder and Washing Soda (intermediate)

In our journey through everyday chemistry, we encounter two salts that are indispensable for hygiene and industry: Bleaching Powder and Washing Soda. While they share common roots in sodium chloride (common salt) chemistry, their roles are distinct—one acts primarily as a powerful oxidizing disinfectant, while the other serves as a versatile cleaner and water softener.

Bleaching Powder (Calcium Oxychloride) is produced by the action of chlorine gas on dry slaked lime, Ca(OH)₂. The chlorine used here is actually a byproduct of the electrolysis of brine (the chlor-alkali process). Chemically represented as CaOCl₂, its real-world utility stems from its ability to release chlorine, making it a potent oxidizing agent Science, Class X (NCERT 2025 ed.), Chapter 2, p.30. This makes it vital for sterilizing drinking water by killing germs and for removing color from cotton, linen, and wood pulp in the textile and paper industries Science, Class X (NCERT 2025 ed.), Chapter 2, p.31.

Washing Soda, or Sodium Carbonate (Na₂CO₃·10H₂O), is another essential salt. It is obtained by the recrystallization of sodium carbonate, which itself can be produced by heating baking soda. Beyond its obvious use as a laundry detergent, washing soda plays a critical role in heavy industry. It is used in the manufacturing of glass, soap, and paper, and serves as the precursor for chemical compounds like borax Science, Class X (NCERT 2025 ed.), Chapter 2, p.32. One of its most important functions in chemistry is the removal of permanent hardness of water, allowing soap to lather effectively even in mineral-rich water.

Feature	Bleaching Powder (CaOCl₂)	Washing Soda (Na₂CO₃·10H₂O)
Key Reactant	Chlorine + Slaked Lime	Sodium Carbonate + Water
Primary Action	Oxidation / Disinfection	Cleaning / Softening
Major Use	Purifying drinking water	Removing permanent water hardness

Sources: Science, Class X (NCERT 2025 ed.), Chapter 2: Acids, Bases and Salts, p.30-31; Science, Class X (NCERT 2025 ed.), Chapter 2: Acids, Bases and Salts, p.32

5. Chemistry of Baking Soda (Sodium Bicarbonate) (intermediate)

Sodium hydrogencarbonate (NaHCO₃), commonly known as baking soda, is a staple in both the kitchen and the medicine cabinet. From a chemical perspective, it is classified as a mild, non-corrosive basic salt. This classification is vital for its everyday utility: unlike strong bases such as sodium hydroxide (caustic soda), which can cause chemical burns, baking soda is safe enough to be handled and even ingested in small quantities Science, Class X (NCERT 2025 ed.), Chapter 2, p.31.

One of the most fascinating aspects of baking soda is how it behaves when heated. During the cooking process, sodium hydrogencarbonate undergoes a decomposition reaction. It breaks down to produce sodium carbonate, water, and carbon dioxide gas (CO₂). The chemical equation for this transformation is:
2NaHCO₃ → Na₂CO₃ + H₂O + CO₂
This release of CO₂ is what makes your cakes rise and gives bread its fluffy texture. In the context of cooking harder foods like gram or dal, adding a pinch of baking soda can significantly speed up the softening process Science, Class X (NCERT 2025 ed.), Chapter 2, p.31.

Beyond the kitchen, its chemical properties make it an excellent antacid. Because it is alkaline (with a mild pH of around 8-9), it can effectively neutralize excess hydrochloric acid (HCl) produced in the stomach, providing relief from indigestion and heartburn. Furthermore, its ability to release a heavy blanket of CO₂ when reacting with acids is utilized in soda-acid fire extinguishers to smother flames by cutting off the oxygen supply.

Property	Description
Nature	Mild, non-corrosive basic salt
By-product of Heating	CO₂ gas (causes rising in dough)
Medical Use	Antacid (neutralizes stomach acid)
Safety Use	Soda-acid fire extinguishers

Sources: Science, Class X (NCERT 2025 ed.), Chapter 2: Acids, Bases and Salts, p.31

6. Functional Applications of Baking Soda (exam-level)

Sodium hydrogencarbonate (NaHCO₃), commonly known as baking soda, is a versatile chemical used extensively in households and industries. Unlike strong, caustic bases like sodium hydroxide, baking soda is a mild, non-corrosive basic salt. This property makes it safe for human consumption and skin contact, which is why it is a staple in both the kitchen and the medicine cabinet Science, Class X (NCERT 2025 ed.), Chapter 2, p.31. Chemically, it is produced using the Solvay process and, when heated during cooking, it decomposes to release carbon dioxide gas, which helps in the aeration of dough.

The functional applications of baking soda can be categorized into three primary areas:

• Culinary Uses: It is used to make baking powder, which is a mixture of baking soda and a mild edible acid like tartaric acid. When moistened or heated, these react to produce CO₂, making cakes and bread soft and spongy. Additionally, adding it to legumes like gram or dal reduces cooking time by softening the tough cellulose fibers Science, Class X (NCERT 2025 ed.), Chapter 2, p.31.
• Medicinal Antacid: During indigestion, the stomach produces excess hydrochloric acid (HCl), causing pain and irritation. Being alkaline, sodium hydrogencarbonate acts as an effective antacid by neutralizing the excess acid, providing immediate relief Science, Class X (NCERT 2025 ed.), Chapter 2, p.27.
• Fire Safety: It is the active ingredient in soda-acid fire extinguishers. When the extinguisher is activated, baking soda reacts with an acid (like sulphuric acid) to produce a rapid discharge of carbon dioxide, which smothers the fire by displacing oxygen Science, Class X (NCERT 2025 ed.), Chapter 2, p.36.

Application	Mechanism	Outcome
Baking	NaHCO₃ + H⁺ → CO₂ + H₂O + Salt	Rise and fluffiness in food
Antacid	Neutralization of HCl	Relief from acidity
Fire Safety	Acid-Base reaction	CO₂ production to extinguish flames

Interestingly, the physical properties of baking soda also vary with environment; for instance, its solubility in water increases significantly with temperature, allowing it to dissolve more effectively in hot liquids than in cold water Science, Class VIII (NCERT 2025 ed.), Chapter 9, p.138.

Sources: Science, Class X (NCERT 2025 ed.), Chapter 2: Acids, Bases and Salts, p.27, 31, 36; Science, Class VIII (NCERT 2025 ed.), Chapter 9: The Amazing World of Solutes, Solvents, and Solutions, p.138

7. Solving the Original PYQ (exam-level)

Review the concepts above and try solving the question.