Class 10 Science – Important Compounds
Chapter 2: Acids, Bases and Salts
CBSE • Foundation • Competitive Level | Hindi + English
1. Sodium Hydroxide (NaOH) – सोडियम हाइड्रॉक्साइड
📘 Concept / अवधारणा
Sodium Hydroxide (NaOH) is a strong base, commonly known as
caustic soda. It is highly soluble in water and produces hydroxide ions
in aqueous solution.
सोडियम हाइड्रॉक्साइड एक प्रबल क्षार है, जिसे सामान्यतः कास्टिक सोडा कहा जाता है। यह जल में घुलकर OH⁻ आयन प्रदान करता है।
सोडियम हाइड्रॉक्साइड एक प्रबल क्षार है, जिसे सामान्यतः कास्टिक सोडा कहा जाता है। यह जल में घुलकर OH⁻ आयन प्रदान करता है।
NaOH → Na⁺ + OH⁻
⚗️ Preparation – Chlor-Alkali Process
Aqueous sodium chloride (brine) is electrolysed to produce sodium
hydroxide, chlorine and hydrogen.
सांद्र NaCl विलयन अर्थात् brine के विद्युत अपघटन से NaOH, Cl₂ तथा H₂ प्राप्त होते हैं।
सांद्र NaCl विलयन अर्थात् brine के विद्युत अपघटन से NaOH, Cl₂ तथा H₂ प्राप्त होते हैं।
2NaCl + 2H₂O → 2NaOH + Cl₂ + H₂
Remember: This process is called the Chlor-Alkali Process
because chlorine and alkali (NaOH) are produced.
🏭 Uses / उपयोग
• Manufacture of soaps and detergents.
• Manufacture of artificial fibres such as rayon.
• Paper manufacturing.
• Extraction of aluminium from bauxite.
• Used in many chemical industries.
• साबुन और डिटर्जेंट बनाने में।
• रेयान जैसे कृत्रिम रेशे बनाने में।
• कागज उद्योग में।
• बॉक्साइट से एल्युमिनियम के निष्कर्षण में।
• Manufacture of artificial fibres such as rayon.
• Paper manufacturing.
• Extraction of aluminium from bauxite.
• Used in many chemical industries.
• साबुन और डिटर्जेंट बनाने में।
• रेयान जैसे कृत्रिम रेशे बनाने में।
• कागज उद्योग में।
• बॉक्साइट से एल्युमिनियम के निष्कर्षण में।
🎯 30 MCQ – Multiple Choice Questions
✍️ 30 Subjective Questions – 1 to 6 Marks
1 Mark
1. What is the formula of sodium hydroxide? / सोडियम हाइड्रॉक्साइड का सूत्र क्या है?
1. What is the formula of sodium hydroxide? / सोडियम हाइड्रॉक्साइड का सूत्र क्या है?
NaOH.
1 Mark
2. What is the common name of NaOH?
2. What is the common name of NaOH?
Caustic soda / कास्टिक सोडा.
1 Mark
3. Name the industrial process used to prepare NaOH from brine.
3. Name the industrial process used to prepare NaOH from brine.
Chlor-alkali process.
1 Mark
4. Which gas is released at the anode during electrolysis of brine?
4. Which gas is released at the anode during electrolysis of brine?
Chlorine gas.
1 Mark
5. Which gas is released at the cathode?
5. Which gas is released at the cathode?
Hydrogen gas.
2 Marks
6. Why is NaOH called a strong base?
6. Why is NaOH called a strong base?
NaOH dissociates almost completely in water and produces a high concentration of OH⁻ ions. इसलिए यह प्रबल क्षार है।
2 Marks
7. Write the dissociation equation of NaOH in water.
7. Write the dissociation equation of NaOH in water.
NaOH → Na⁺ + OH⁻
NaOH gives sodium and hydroxide ions in aqueous solution.
2 Marks
8. What is brine?
8. What is brine?
Brine is a concentrated aqueous solution of sodium chloride (NaCl).
2 Marks
9. Give two uses of sodium hydroxide.
9. Give two uses of sodium hydroxide.
Soap manufacture and paper manufacture. It is also used in rayon and aluminium industries.
2 Marks
10. What happens when NaOH reacts with HCl?
10. What happens when NaOH reacts with HCl?
NaOH + HCl → NaCl + H₂O
A neutralization reaction occurs.
3 Marks
11. Explain the chlor-alkali process.
11. Explain the chlor-alkali process.
Brine is electrolysed. Chlorine is produced at the anode, hydrogen at the cathode and sodium hydroxide remains in solution.
2NaCl + 2H₂O → 2NaOH + Cl₂ + H₂
2NaCl + 2H₂O → 2NaOH + Cl₂ + H₂
3 Marks
12. Write three important uses of NaOH.
12. Write three important uses of NaOH.
Soap/detergent manufacture, paper manufacture and extraction of aluminium from bauxite.
3 Marks
13. Why is NaOH solution basic?
13. Why is NaOH solution basic?
NaOH ionizes in water and produces OH⁻ ions. These ions give the solution its basic character and turn red litmus blue.
3 Marks
14. Write the products obtained during electrolysis of brine.
14. Write the products obtained during electrolysis of brine.
Sodium hydroxide, chlorine gas and hydrogen gas.
3 Marks
15. Differentiate between NaOH and NaCl.
15. Differentiate between NaOH and NaCl.
NaOH is a strong base, whereas NaCl is a neutral salt. NaOH contains OH⁻ ions in aqueous solution; NaCl gives Na⁺ and Cl⁻ ions.
4 Marks
16. Explain the chemical reactions occurring during chlor-alkali process.
16. Explain the chemical reactions occurring during chlor-alkali process.
At the cathode: 2H₂O + 2e⁻ → H₂ + 2OH⁻
At the anode: 2Cl⁻ → Cl₂ + 2e⁻
Na⁺ combines with OH⁻ to form NaOH.
Overall: 2NaCl + 2H₂O → 2NaOH + Cl₂ + H₂
At the anode: 2Cl⁻ → Cl₂ + 2e⁻
Na⁺ combines with OH⁻ to form NaOH.
Overall: 2NaCl + 2H₂O → 2NaOH + Cl₂ + H₂
4 Marks
17. Explain four uses of sodium hydroxide.
17. Explain four uses of sodium hydroxide.
NaOH is used in soap and detergent manufacture, paper manufacture, rayon production and aluminium extraction from bauxite.
4 Marks
18. Why is the chlor-alkali process commercially important?
18. Why is the chlor-alkali process commercially important?
It simultaneously produces three valuable industrial chemicals: NaOH, chlorine and hydrogen.
4 Marks
19. A student adds NaOH to HCl. What type of reaction occurs? Explain.
19. A student adds NaOH to HCl. What type of reaction occurs? Explain.
It is a neutralization reaction.
NaOH + HCl → NaCl + H₂O
The acid and base react to form salt and water.
NaOH + HCl → NaCl + H₂O
The acid and base react to form salt and water.
4 Marks
20. Why should concentrated NaOH be handled carefully?
20. Why should concentrated NaOH be handled carefully?
Because concentrated NaOH is highly corrosive and can cause severe burns to skin and tissues.
5 Marks
21. Describe preparation, properties and uses of sodium hydroxide.
21. Describe preparation, properties and uses of sodium hydroxide.
NaOH is prepared by electrolysis of brine. It is a strong, highly soluble and corrosive base. It produces OH⁻ ions in water. It is used in soap, paper, rayon and aluminium industries.
5 Marks
22. Explain the chlor-alkali process with equation.
22. Explain the chlor-alkali process with equation.
Concentrated NaCl solution is electrolysed. Chlorine forms at the anode and hydrogen at the cathode. NaOH remains in solution.
2NaCl + 2H₂O → 2NaOH + Cl₂ + H₂
2NaCl + 2H₂O → 2NaOH + Cl₂ + H₂
5 Marks
23. Explain why electrolysis of brine is called chlor-alkali process.
23. Explain why electrolysis of brine is called chlor-alkali process.
Because chlorine and an alkali, sodium hydroxide, are produced. Hydrogen is also obtained as a useful by-product.
5 Marks
24. Write an application-based note on NaOH in industry.
24. Write an application-based note on NaOH in industry.
NaOH is a major industrial alkali used for soaps, detergents, paper, rayon and processing bauxite for aluminium extraction.
6 Marks
25. Explain the complete chlor-alkali process with electrode reactions.
25. Explain the complete chlor-alkali process with electrode reactions.
Brine contains Na⁺ and Cl⁻ ions. During electrolysis, Cl⁻ ions are oxidized at the anode to Cl₂. Water is reduced at the cathode to H₂ and OH⁻. Na⁺ combines with OH⁻ to produce NaOH.
Anode: 2Cl⁻ → Cl₂ + 2e⁻
Cathode: 2H₂O + 2e⁻ → H₂ + 2OH⁻
Overall: 2NaCl + 2H₂O → 2NaOH + Cl₂ + H₂
Anode: 2Cl⁻ → Cl₂ + 2e⁻
Cathode: 2H₂O + 2e⁻ → H₂ + 2OH⁻
Overall: 2NaCl + 2H₂O → 2NaOH + Cl₂ + H₂
6 Marks
26. Discuss the physical and chemical properties of NaOH.
26. Discuss the physical and chemical properties of NaOH.
NaOH is a white solid, highly soluble in water, strongly alkaline and corrosive. It dissociates into Na⁺ and OH⁻ ions and neutralizes acids.
6 Marks
27. Explain five major industrial uses of NaOH.
27. Explain five major industrial uses of NaOH.
Soap, detergents, paper, rayon and aluminium extraction are major applications.
6 Marks
28. Compare NaOH with baking soda.
28. Compare NaOH with baking soda.
NaOH is a strong base and highly corrosive, whereas NaHCO₃ is a mild basic salt. NaOH is mainly industrial, while baking soda is widely used in cooking and as an antacid.
6 Marks
29. A factory requires chlorine, hydrogen and sodium hydroxide. Which process should it use and why?
29. A factory requires chlorine, hydrogen and sodium hydroxide. Which process should it use and why?
The chlor-alkali process should be used because electrolysis of brine produces all three substances simultaneously.
6 Marks
30. Write a comprehensive note on sodium hydroxide.
30. Write a comprehensive note on sodium hydroxide.
NaOH is caustic soda and a strong alkali. It is prepared by the chlor-alkali process from brine. It gives OH⁻ ions in water, is corrosive and has many industrial uses such as soap, paper, rayon and aluminium manufacture.
2. Bleaching Powder (CaOCl₂) – ब्लीचिंग पाउडर
📘 Concept / अवधारणा
Bleaching powder is commonly represented by the formula
CaOCl₂ and is known as calcium oxychloride.
It is prepared by passing chlorine gas over dry slaked lime.
Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O
🏭 Uses / उपयोग
• Disinfection of drinking water.
• Bleaching cotton and linen in textile industries.
• Bleaching wood pulp in paper industries.
• Oxidizing agent in chemical industries.
• Bleaching cotton and linen in textile industries.
• Bleaching wood pulp in paper industries.
• Oxidizing agent in chemical industries.
Important: Bleaching powder is used for disinfection because it can release chlorine/active chlorine species.
🎯 30 MCQ
✍️ 30 Subjective Questions – 1 to 6 Marks
1 Mark
1. Write the formula of bleaching powder.
1. Write the formula of bleaching powder.
CaOCl₂.
1 Mark
2. What is the common chemical name of bleaching powder?
2. What is the common chemical name of bleaching powder?
Calcium oxychloride.
1 Mark
3. Which gas is used to prepare bleaching powder?
3. Which gas is used to prepare bleaching powder?
Chlorine gas.
1 Mark
4. Which base is used in its preparation?
4. Which base is used in its preparation?
Slaked lime, Ca(OH)₂.
1 Mark
5. Name one use of bleaching powder.
5. Name one use of bleaching powder.
Disinfection of drinking water.
2 Marks
6. Write the preparation equation of bleaching powder.
6. Write the preparation equation of bleaching powder.
Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O
2 Marks
7. Why is bleaching powder used in drinking water?
7. Why is bleaching powder used in drinking water?
It releases active chlorine species that destroy many harmful microorganisms.
2 Marks
8. Give two uses of bleaching powder.
8. Give two uses of bleaching powder.
Water disinfection and bleaching of cotton/linen.
2 Marks
9. What happens when chlorine reacts with dry slaked lime?
9. What happens when chlorine reacts with dry slaked lime?
Bleaching powder is formed along with water.
2 Marks
10. Why is bleaching powder considered an oxidizing agent?
10. Why is bleaching powder considered an oxidizing agent?
Because its active chlorine can participate in oxidation reactions.
3 Marks
11. Explain preparation of bleaching powder.
11. Explain preparation of bleaching powder.
Dry slaked lime is treated with chlorine gas under suitable conditions to form calcium oxychloride.
Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O
Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O
3 Marks
12. Write three uses of bleaching powder.
12. Write three uses of bleaching powder.
Water disinfection, textile bleaching and paper-pulp bleaching.
3 Marks
13. What is the role of chlorine in bleaching powder?
13. What is the role of chlorine in bleaching powder?
Chlorine provides the active chlorine responsible for bleaching and disinfection.
3 Marks
14. Why should bleaching powder be stored properly?
14. Why should bleaching powder be stored properly?
It can lose available chlorine over time, especially under unsuitable storage conditions.
3 Marks
15. Distinguish between bleaching powder and slaked lime.
15. Distinguish between bleaching powder and slaked lime.
Bleaching powder is calcium oxychloride and has bleaching/disinfecting properties. Slaked lime is Ca(OH)₂ and is used in construction and several neutralization processes.
4 Marks
16. Explain the importance of bleaching powder in public health.
16. Explain the importance of bleaching powder in public health.
It is widely used to disinfect drinking water and reduce microbial contamination, helping prevent water-borne diseases.
4 Marks
17. Explain four uses of bleaching powder.
17. Explain four uses of bleaching powder.
Water disinfection, textile bleaching, paper-pulp bleaching and use as an oxidizing agent.
4 Marks
18. Write the preparation equation and identify reactants.
18. Write the preparation equation and identify reactants.
Reactants are chlorine and dry slaked lime.
Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O
Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O
4 Marks
19. Why is chlorine important in bleaching powder?
19. Why is chlorine important in bleaching powder?
Chlorine contributes active chlorine species responsible for oxidation, bleaching and disinfection.
4 Marks
20. Explain bleaching action at the school level.
20. Explain bleaching action at the school level.
Bleaching powder provides active chlorine that oxidizes coloured substances, converting them into less-coloured or colourless products.
5 Marks
21. Describe preparation, properties and uses of bleaching powder.
21. Describe preparation, properties and uses of bleaching powder.
It is prepared from chlorine and dry slaked lime. It is an oxidizing/bleaching material and is used for water disinfection and bleaching textile and paper materials.
5 Marks
22. Explain why bleaching powder is suitable for water treatment.
22. Explain why bleaching powder is suitable for water treatment.
It provides active chlorine, which kills or inactivates many microorganisms in water.
5 Marks
23. Compare bleaching powder and chlorine gas as disinfectants.
23. Compare bleaching powder and chlorine gas as disinfectants.
Both provide chlorine-based disinfection. Bleaching powder is easier to store and transport than chlorine gas, making it convenient for many applications.
5 Marks
24. Explain the industrial importance of bleaching powder.
24. Explain the industrial importance of bleaching powder.
It is important in water treatment, textile bleaching, paper manufacturing and chemical oxidation processes.
6 Marks
25. Explain bleaching powder in detail.
25. Explain bleaching powder in detail.
Bleaching powder is calcium oxychloride, commonly represented as CaOCl₂. It is prepared by passing chlorine over dry slaked lime. It has bleaching and disinfecting properties and is used for drinking water, textiles and paper pulp.
6 Marks
26. Explain its preparation with chemical equation and uses.
26. Explain its preparation with chemical equation and uses.
Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O
Uses include water disinfection, bleaching cotton/linen, paper-pulp bleaching and oxidation.
Uses include water disinfection, bleaching cotton/linen, paper-pulp bleaching and oxidation.
6 Marks
27. A village has contaminated drinking water. Which compound can be used and why?
27. A village has contaminated drinking water. Which compound can be used and why?
Bleaching powder can be used because it releases active chlorine that helps destroy many microorganisms.
6 Marks
28. Explain the bleaching and disinfecting properties of bleaching powder.
28. Explain the bleaching and disinfecting properties of bleaching powder.
Its active chlorine oxidizes coloured compounds and damages/inactivates microorganisms, producing bleaching and disinfecting effects.
6 Marks
29. Write a comprehensive note on calcium oxychloride.
29. Write a comprehensive note on calcium oxychloride.
Calcium oxychloride is commonly represented as CaOCl₂ and is called bleaching powder. It is prepared using chlorine and slaked lime and is extensively used for bleaching and disinfection.
6 Marks
30. Why is bleaching powder an important chemical in daily life and industry?
30. Why is bleaching powder an important chemical in daily life and industry?
Because it combines convenient chlorine-based disinfection with bleaching applications in water treatment, textiles and paper industries.
3. Baking Soda (NaHCO₃) – बेकिंग सोडा
📘 Concept / अवधारणा
Baking soda is sodium hydrogen carbonate (NaHCO₃).
It is a mild basic salt and is widely used in cooking, baking and as an
ingredient of some antacids.
⚗️ Preparation
In the Solvay process, sodium hydrogen carbonate is precipitated from
a solution containing sodium chloride, ammonia and carbon dioxide.
NaCl + H₂O + CO₂ + NH₃ → NH₄Cl + NaHCO₃
🔥 Heating of Baking Soda
2NaHCO₃ → Na₂CO₃ + H₂O + CO₂
The released CO₂ helps dough rise and makes cakes and bread soft and
spongy.
🏭 Uses / उपयोग
• Baking powder.
• Antacid formulations.
• Fire extinguishers in traditional school-level examples.
• Mild cleaning applications.
• Antacid formulations.
• Fire extinguishers in traditional school-level examples.
• Mild cleaning applications.
🎯 30 MCQ
✍️ 30 Subjective Questions – 1 to 6 Marks
1 Mark
1. Write the formula of baking soda.
1. Write the formula of baking soda.
NaHCO₃.
1 Mark
2. Give the chemical name of baking soda.
2. Give the chemical name of baking soda.
Sodium hydrogen carbonate.
1 Mark
3. Is baking soda acidic or basic in nature?
3. Is baking soda acidic or basic in nature?
It is mildly basic.
1 Mark
4. Which gas is released when baking soda is heated?
4. Which gas is released when baking soda is heated?
Carbon dioxide.
1 Mark
5. Write one use of baking soda.
5. Write one use of baking soda.
It is used in baking powder.
2 Marks
6. What happens when NaHCO₃ is heated?
6. What happens when NaHCO₃ is heated?
2NaHCO₃ → Na₂CO₃ + H₂O + CO₂
2 Marks
7. Why is baking soda used in cakes?
7. Why is baking soda used in cakes?
On heating, it releases CO₂, which makes the dough rise and become porous.
2 Marks
8. Why is baking soda used as an antacid?
8. Why is baking soda used as an antacid?
It is a mild base and can neutralize excess stomach acid.
2 Marks
9. What is baking powder?
9. What is baking powder?
It is generally a mixture containing baking soda and an edible weak acid, commonly represented in school texts by tartaric acid, used to release CO₂ during baking.
2 Marks
10. Write two uses of baking soda.
10. Write two uses of baking soda.
Baking and antacid formulations.
3 Marks
11. Explain the thermal decomposition of baking soda.
11. Explain the thermal decomposition of baking soda.
On heating, sodium hydrogen carbonate decomposes to sodium carbonate, water and carbon dioxide.
2NaHCO₃ → Na₂CO₃ + H₂O + CO₂
2NaHCO₃ → Na₂CO₃ + H₂O + CO₂
3 Marks
12. Explain the role of CO₂ in baking.
12. Explain the role of CO₂ in baking.
CO₂ bubbles expand on heating and create pores, making bread/cake rise and become soft and spongy.
3 Marks
13. Why is NaHCO₃ called a mild base?
13. Why is NaHCO₃ called a mild base?
It has basic properties but is much less caustic than strong bases such as NaOH.
3 Marks
14. Give three applications of baking soda.
14. Give three applications of baking soda.
Baking powder, antacid formulations and certain cleaning/fire-extinguisher applications.
3 Marks
15. What happens when baking soda reacts with an acid?
15. What happens when baking soda reacts with an acid?
NaHCO₃ + HCl → NaCl + H₂O + CO₂
4 Marks
16. Explain why baking soda is used in baking powder.
16. Explain why baking soda is used in baking powder.
Baking soda reacts with an edible acid or decomposes on heating to release CO₂. The gas forms bubbles in the dough and causes it to rise.
4 Marks
17. Explain the reaction of baking soda with HCl.
17. Explain the reaction of baking soda with HCl.
NaHCO₃ + HCl → NaCl + H₂O + CO₂
The reaction produces salt, water and carbon dioxide gas.
4 Marks
18. Why is baking soda useful as an antacid?
18. Why is baking soda useful as an antacid?
It neutralizes excess hydrochloric acid in the stomach because it is a mild base.
4 Marks
19. Explain why excessive baking soda should not be consumed unnecessarily.
19. Explain why excessive baking soda should not be consumed unnecessarily.
Although it is a mild base, excessive intake can disturb normal acid-base balance and cause unwanted effects. It should be used appropriately.
4 Marks
20. Differentiate between NaHCO₃ and NaOH.
20. Differentiate between NaHCO₃ and NaOH.
NaHCO₃ is a mild basic salt used in baking and antacids, whereas NaOH is a strong, highly corrosive base mainly used industrially.
5 Marks
21. Explain preparation, properties and uses of baking soda.
21. Explain preparation, properties and uses of baking soda.
NaHCO₃ is obtained industrially in the Solvay process. It is a mild base, reacts with acids to release CO₂ and is used in baking and antacid formulations.
5 Marks
22. Explain the importance of thermal decomposition of NaHCO₃.
22. Explain the importance of thermal decomposition of NaHCO₃.
Heating produces Na₂CO₃, water and CO₂. The CO₂ is particularly useful in baking because it creates a porous structure.
5 Marks
23. Explain the chemistry of baking powder.
23. Explain the chemistry of baking powder.
Baking powder contains sodium hydrogen carbonate and an edible acid. On moistening/heating, they react to produce CO₂, which makes baked products rise.
5 Marks
24. Compare baking soda and baking powder.
24. Compare baking soda and baking powder.
Baking soda is NaHCO₃. Baking powder contains baking soda plus an edible acid and is formulated to release CO₂ during baking.
6 Marks
25. Explain baking soda with chemical equations and uses.
25. Explain baking soda with chemical equations and uses.
Formula: NaHCO₃.
With acid: NaHCO₃ + HCl → NaCl + H₂O + CO₂
On heating: 2NaHCO₃ → Na₂CO₃ + H₂O + CO₂
Uses: baking, antacid formulations and other household/industrial applications.
With acid: NaHCO₃ + HCl → NaCl + H₂O + CO₂
On heating: 2NaHCO₃ → Na₂CO₃ + H₂O + CO₂
Uses: baking, antacid formulations and other household/industrial applications.
6 Marks
26. Explain why cakes become soft and spongy.
26. Explain why cakes become soft and spongy.
Baking soda generates CO₂. The gas expands during heating and forms numerous small pores in the dough, producing a light and spongy texture.
6 Marks
27. A student adds dilute HCl to NaHCO₃. What observations will occur?
27. A student adds dilute HCl to NaHCO₃. What observations will occur?
Effervescence occurs because CO₂ gas is released. The products are NaCl and H₂O along with CO₂.
6 Marks
28. Explain the industrial preparation of baking soda in the Solvay process.
28. Explain the industrial preparation of baking soda in the Solvay process.
In the Solvay process, brine is treated in the presence of ammonia and carbon dioxide. Sodium hydrogen carbonate precipitates because of its lower solubility and can be separated.
6 Marks
29. Explain the reaction of baking soda with acids and its practical importance.
29. Explain the reaction of baking soda with acids and its practical importance.
NaHCO₃ reacts with acids to form salt, water and CO₂. This property is useful in baking, where CO₂ provides leavening, and in mild antacid applications.
6 Marks
30. Write a comprehensive note on sodium hydrogen carbonate.
30. Write a comprehensive note on sodium hydrogen carbonate.
Sodium hydrogen carbonate (NaHCO₃) is baking soda. It is mildly basic, reacts with acids to produce CO₂ and decomposes on heating. Its major applications include baking and antacid formulations.
4. Washing Soda (Na₂CO₃·10H₂O) – वॉशिंग सोडा
📘 Concept / अवधारणा
Washing soda is sodium carbonate decahydrate.
Its chemical formula is Na₂CO₃·10H₂O.
It is a basic salt containing ten molecules of water of crystallisation.
⚗️ Preparation
Sodium carbonate can be obtained from sodium hydrogen carbonate by heating.
The anhydrous sodium carbonate can then crystallise with ten molecules of water.
2NaHCO₃ → Na₂CO₃ + H₂O + CO₂
Na₂CO₃ + 10H₂O → Na₂CO₃·10H₂O
🏭 Uses / उपयोग
• Cleaning agent.
• Removal of permanent hardness of water.
• Manufacture of glass, soap and paper.
• Used in chemical industries.
• Used as a laboratory reagent.
• Removal of permanent hardness of water.
• Manufacture of glass, soap and paper.
• Used in chemical industries.
• Used as a laboratory reagent.
💧 Water Hardness
Washing soda can remove permanent hardness by precipitating calcium and
magnesium ions as insoluble carbonates.
Na₂CO₃ + CaCl₂ → CaCO₃↓ + 2NaCl
🎯 30 MCQ
✍️ 30 Subjective Questions – 1 to 6 Marks
1 Mark
1. Write the formula of washing soda.
1. Write the formula of washing soda.
Na₂CO₃·10H₂O.
1 Mark
2. Give the chemical name of washing soda.
2. Give the chemical name of washing soda.
Sodium carbonate decahydrate.
1 Mark
3. How many water molecules are present in washing soda?
3. How many water molecules are present in washing soda?
Ten molecules.
1 Mark
4. What is water of crystallisation?
4. What is water of crystallisation?
The fixed number of water molecules chemically associated with a salt crystal.
1 Mark
5. Name one use of washing soda.
5. Name one use of washing soda.
Removal of permanent hardness of water.
2 Marks
6. What is washing soda used for?
6. What is washing soda used for?
It is used as a cleaning agent and for removing permanent hardness of water.
2 Marks
7. Why is washing soda called decahydrate?
7. Why is washing soda called decahydrate?
Because each formula unit contains ten molecules of crystallisation water.
2 Marks
8. Write the formula of anhydrous sodium carbonate.
8. Write the formula of anhydrous sodium carbonate.
Na₂CO₃.
2 Marks
9. What is water of crystallisation?
9. What is water of crystallisation?
It is the definite amount of water present in the crystalline structure of a salt.
2 Marks
10. Give two industrial uses of washing soda.
10. Give two industrial uses of washing soda.
Manufacture of glass and manufacture of soap/paper.
3 Marks
11. Explain formation of washing soda from sodium carbonate.
11. Explain formation of washing soda from sodium carbonate.
Na₂CO₃ + 10H₂O → Na₂CO₃·10H₂O
Crystallisation with ten water molecules produces washing soda.
3 Marks
12. How does washing soda help remove permanent hardness?
12. How does washing soda help remove permanent hardness?
Carbonate ions react with Ca²⁺ and Mg²⁺ ions to form insoluble carbonates, which can be removed.
3 Marks
13. Write the reaction of sodium carbonate with calcium chloride.
13. Write the reaction of sodium carbonate with calcium chloride.
Na₂CO₃ + CaCl₂ → CaCO₃↓ + 2NaCl
3 Marks
14. Mention three uses of washing soda.
14. Mention three uses of washing soda.
Cleaning, removal of permanent hardness and manufacture of glass/soap/paper.
3 Marks
15. Differentiate between baking soda and washing soda.
15. Differentiate between baking soda and washing soda.
Baking soda is NaHCO₃, whereas washing soda is Na₂CO₃·10H₂O. Baking soda is used in baking; washing soda is mainly used for cleaning and water softening.
4 Marks
16. Explain the role of washing soda in removing hardness of water.
16. Explain the role of washing soda in removing hardness of water.
Na₂CO₃ supplies CO₃²⁻ ions. These react with Ca²⁺/Mg²⁺ ions and form insoluble carbonates, thereby removing these ions from water.
4 Marks
17. Explain water of crystallisation with example.
17. Explain water of crystallisation with example.
Water of crystallisation is fixed water present in salt crystals. Washing soda, Na₂CO₃·10H₂O, contains ten water molecules per formula unit.
4 Marks
18. Write four uses of washing soda.
18. Write four uses of washing soda.
Cleaning, water softening, glass manufacture and soap/paper manufacture.
4 Marks
19. What happens when sodium carbonate reacts with calcium chloride?
19. What happens when sodium carbonate reacts with calcium chloride?
Na₂CO₃ + CaCl₂ → CaCO₃↓ + 2NaCl
Insoluble calcium carbonate precipitates.
4 Marks
20. Why is washing soda a useful basic salt?
20. Why is washing soda a useful basic salt?
Its carbonate ions make it alkaline and allow it to react with acidic substances and hardness-producing ions.
5 Marks
21. Describe preparation, properties and uses of washing soda.
21. Describe preparation, properties and uses of washing soda.
Sodium carbonate crystallises with ten water molecules to form Na₂CO₃·10H₂O. It is basic and is used for cleaning, water softening and glass/soap/paper industries.
5 Marks
22. Explain permanent hardness and its removal using washing soda.
22. Explain permanent hardness and its removal using washing soda.
Permanent hardness is mainly due to soluble calcium and magnesium salts such as chlorides/sulfates. Washing soda supplies CO₃²⁻ ions that precipitate CaCO₃ and MgCO₃.
5 Marks
23. Explain the importance of water of crystallisation.
23. Explain the importance of water of crystallisation.
It forms part of the crystal structure and may influence the physical properties of hydrated salts. Washing soda contains ten water molecules.
5 Marks
24. Compare sodium carbonate and washing soda.
24. Compare sodium carbonate and washing soda.
Na₂CO₃ is anhydrous sodium carbonate. Na₂CO₃·10H₂O is hydrated sodium carbonate, called washing soda.
6 Marks
25. Explain washing soda in detail.
25. Explain washing soda in detail.
Washing soda is sodium carbonate decahydrate, Na₂CO₃·10H₂O. It contains ten water molecules of crystallisation. It is used as a cleaning agent, for water softening and in glass, soap and paper industries.
6 Marks
26. Explain the chemistry of permanent hardness removal by washing soda.
26. Explain the chemistry of permanent hardness removal by washing soda.
Washing soda dissociates to provide carbonate ions:
Na₂CO₃ → 2Na⁺ + CO₃²⁻
Ca²⁺ + CO₃²⁻ → CaCO₃↓
Mg²⁺ + CO₃²⁻ → MgCO₃↓
Thus hardness-producing ions are removed as precipitates.
Na₂CO₃ → 2Na⁺ + CO₃²⁻
Ca²⁺ + CO₃²⁻ → CaCO₃↓
Mg²⁺ + CO₃²⁻ → MgCO₃↓
Thus hardness-producing ions are removed as precipitates.
6 Marks
27. Explain water of crystallisation using washing soda as an example.
27. Explain water of crystallisation using washing soda as an example.
Washing soda has formula Na₂CO₃·10H₂O. The dot indicates ten water molecules associated with each formula unit in the crystalline structure.
6 Marks
28. Write six important applications of washing soda.
28. Write six important applications of washing soda.
Cleaning, permanent water-softening, glass manufacture, soap manufacture, paper manufacture and chemical/laboratory applications.
6 Marks
29. A water sample contains Ca²⁺ ions causing hardness. How can washing soda help?
29. A water sample contains Ca²⁺ ions causing hardness. How can washing soda help?
Add sodium carbonate. CO₃²⁻ ions react with Ca²⁺ to form insoluble CaCO₃, which precipitates and can be separated.
6 Marks
30. Write a comprehensive note on washing soda.
30. Write a comprehensive note on washing soda.
Washing soda is Na₂CO₃·10H₂O. It is sodium carbonate decahydrate and contains water of crystallisation. It is a basic salt used for cleaning, removal of permanent hardness and manufacture of glass, soap and paper.
