CG Board Class 10 Science Chapter 17 Solutions: Chemistry in Daily Life (दैनिक जीवन में रसायन) (2026-27)

When water containing dissolved magnesium hydrogencarbonate is boiled, the soluble salt undergoes thermal decomposition and precipitates out as insoluble magnesium carbonate. This removes temporary hardness from water.

Chemical Equation:

Mg(HCO₃)₂(aq) → [Boiling] MgCO₃↓ + H_2O(l) + CO₂↑

Iodine is an essential micronutrient required by the human body to synthesize thyroid hormones. Iodine is added to common salt in the form of potassium iodate (KIO₃) during the purification process to prevent iodine deficiency disorders such as goitre.

Sample ‘B’** is hard water.

Reason: Hardness in water is caused specifically by dissolved salts (sulphates, chlorides, or hydrogencarbonates) of calcium or magnesium. Since sample ‘B’ contains dissolved magnesium sulphate (MgSO₄), it will form scum with soap rather than lather. Sample ‘A’ contains a sodium salt (NaHCO₃), which does not cause hardness.

Two natural sources of common salt (sodium chloride, NaCl) are

1. Sea Water: Contains 30-35 g of dissolved salts per liter, primarily sodium chloride.
2. Rock Salt Mines: Underground salt deposits formed by the drying up of ancient seas or oceans.

Sodium hydrogencarbonate (NaHCO₃) is a mild basic/alkaline salt. Because its pH is greater than 7, it reacts with excess acids to form salt, water, and carbon dioxide gas, thereby neutralizing acidity.

10H_2O signifies the water of crystallization, which is the fixed number of water molecules bound into one formula unit of the crystalline sodium carbonate salt.

No, it does not make the washing soda wet; washing soda remains a dry, white crystalline solid in this state.

Chemical Formula:** NaHCO₃ (Sodium hydrogencarbonate)

• Two Uses:

1. In Making Baking Powder: Mixed with tartaric acid to make cakes and breads soft and spongy.
2. As an Antacid: Used to neutralize excess stomach acid and relieve acidity.

Efflorescence** is the property of crystalline washing soda (Na_2CO₃ · 10H_2O) losing 9 molecules of its water of crystallization when exposed to open air, turning into a white powder of sodium carbonate monohydrate (Na_2CO₃ · H_2O).

Na_2CO₃ · 10H_2O(s) → [Open air] Na_2CO₃ · H_2O(s) + 9H_2O

Baking powder is a mixture of baking soda (sodium hydrogencarbonate, NaHCO₃) and a mild edible acid like tartaric acid.

Plaster of Paris (CaSO₄ · 1/2H_2O) when mixed with water rehydrates and sets into a hard, rigid mass of gypsum (CaSO₄ · 2H_2O). This hardening property supports and keeps fractured bones in the correct alignment.

Dry slaked lime** (calcium hydroxide, Ca(OH)₂) reacts with chlorine gas to produce bleaching powder.

Ca(OH)₂(s) + Cl₂(g) → CaOCl₂(s) + H_2O(g)

2-3\%

Cullets (broken pieces of glass) act as a flux in glass manufacturing. They lower the melting point of the raw material mixture (batch), reducing fuel consumption and speeding up the melting process in the tank furnace.

Glass is not a definite chemical compound with a fixed stoichiometry; rather, it is a non-crystalline homogeneous mixture of metal silicates. Because it is a mixture, its structural bonding varies, and it behaves as a super-cooled liquid rather than a sharp crystalline solid, giving it no fixed melting point.

1. Immediately after shaking, test tube A (water + oil) shows rapid separation of oil into a distinct upper layer, whereas test tube B (water + oil + soap) forms a uniform cloudy emulsion.
2. Upon sitting undisturbed, the oil layer separates out first in test tube A. In test tube B, soap molecules surround the oil droplets to form stable micelles, keeping the oil suspended in water.

Soap in Hard Water:** Produces very little lather and forms a sticky white curdy precipitate (scum) because calcium and magnesium ions precipitate soap fatty acid ions.

• Detergent in Hard Water: Produces abundant foam and no scum because the charged ends of detergent sulphonic acid salts do not form insoluble precipitates with Ca²⁺ or Mg²⁺ ions.

No.** Detergents give abundant foam equally in both soft water and hard water because they do not form precipitates with the calcium or magnesium ions present in hard water. Therefore, they cannot be used to distinguish hard water from soft water.

When soap is applied, its molecules wrap around oily dirt particles to form micelles colloidal suspension in water. Mechanical scrubbing or beating helps detach these micelle-entrapped dirt clusters from the fabric fibers so they can be easily rinsed away with water.

(i) The chemical formula of baking soda is:**

(a) NaHSO₄

(b) Na_2CO₃

(c) NaHCO₃

(d) Na_2CO₃ · 10H_2O

• Correct Option: (c) NaHCO₃
• Explanation: Baking soda is chemically sodium hydrogencarbonate with formula NaHCO₃.

Soft Water:** Water that produces abundant lather quickly and easily when mixed with soap (e.g., rain water, distilled water).

• Hard Water: Water that takes a long time to produce lather with soap and forms an insoluble sticky precipitate (scum) due to dissolved salts of calcium or magnesium.

Causes of Hardness:** Hardness is caused by dissolved salts of calcium (Ca²⁺) or magnesium (Mg²⁺), such as hydrogencarbonates, sulphates, or chlorides.

• Types of Hardness: There are two types of hardness

1. Temporary Hardness: Caused by dissolved calcium or magnesium hydrogencarbonates [Ca(HCO₃)₂, Mg(HCO₃)₂]. It can be removed by boiling or by adding limewater.
2. Permanent Hardness: Caused by dissolved calcium or magnesium chlorides or sulphates (CaCl₂, MgCl₂, CaSO₄, MgSO₄). It cannot be removed by boiling.

At 4°C, liquid water reaches its maximum density of 1 g/mL, whereas ice at 0°C has a lower density of 0.9 g/mL. Consequently, ice floats on top of rivers and lakes. Because ice is a thermal insulator, it insulates the deeper water below from the freezing atmospheric cold. The water under the top ice layer remains liquid, allowing aquatic plants and animals to survive comfortably.

Baking powder is a solid dry mixture of baking soda (NaHCO₃) and tartaric acid.

When baking powder is mixed with water or heated during baking, the sodium hydrogencarbonate reacts with hydrogen ions (H^+) from tartaric acid

NaHCO₃ + H^+ → CO₂↑ + H_2O + Sodium salt of acid

The released carbon dioxide (CO₂) gas expands and bubbles up through the dough, making the cake rise and become soft and spongy.

Preparation Process:** Plaster of Paris is produced by heating gypsum (CaSO₄ · 2H_2O) at 100°C (373 K).

CaSO₄ · 2H_2O → [100°C] CaSO₄ · 1/2H_2O + 11/2H_2O

• Reason for Air-tight Storage: Plaster of Paris absorbs moisture from damp air and converts back into a hard solid mass of gypsum, ruining its setting utility. Thus, it must be stored in moisture-proof, air-tight containers.

Chemical Name:** Sodium carbonate decahydrate (Na_2CO₃ · 10H_2O).

• Three Main Raw Materials:

1. Sodium chloride (NaCl)
2. Ammonia (NH₃)
3. Carbon dioxide (CO₂) / Limestone (CaCO₃)

(i) Name the compound.**

(ii) Which gas is released when the compound is left out in open air? Give the balanced equation for this reaction.

(i)

(i) Compound Name: Bleaching powder (Chemical name: Calcium oxychloride, CaOCl₂).

(ii) Gas Released: Chlorine gas (Cl₂).

When exposed to air, it reacts with carbon dioxide gas to release chlorine

CaOCl₂(s) + CO₂(g) → CaCO₃(s) + Cl₂↑

(i) Write the chemical equation for the reaction which takes place on heating.**

(ii) Why is ‘X’ used as an antacid?

(i)

• Identification: ‘X’ is Sodium hydrogencarbonate (NaHCO₃); ‘Y’ is Carbon dioxide gas (CO₂).

(i) Chemical Equation on Heating:

2NaHCO₃ → [Heat] Na_2CO₃ + H_2O + CO₂↑

(ii) Reason for Antacid Use: ‘X’ (NaHCO₃) is a mild alkaline salt that neutralizes excess hydrochloric acid in the stomach to form salt, water, and CO₂, giving fast relief from hyperacidity.

(i) Necessary materials**

(ii) Substances that give or impart colour to glass

(iii) The chemical reaction taking place in tank furnace

(i)

(iii)

(i) Necessary Raw Materials: Silica (sand), Alkali metal carbonate (Na_2CO₃ or K_2CO₃), Divalent metal salt (limestone CaCO₃ or litharge PbO), and Cullets (broken glass pieces as flux).

(ii) Colouring Substances:

• Green: Chromium oxide (Cr_2O₃)
• Yellow: Cadmium sulphide (CdS)
• Red: Copper oxide (Cu_2O)
• Purple: Manganese oxide (MnO₂)
• Blue: Cobalt oxide (CoO)

(iii) Reactions in Tank Furnace (at 1400°C):

Na_2CO₃ + SiO₂ → Na_2SiO₃ + CO₂↑

CaCO₃ + SiO₂ → CaSiO₃ + CO₂↑

Na_2SiO₃ + CaSiO₃ + 4SiO₂ → Na_2O · CaO · 6SiO₂ (Glass)

The raw materials for cement production are limestone (CaCO₃), clay, and gypsum.

1. Pulverization & Mixing: 3 parts limestone and 1 part clay are finely pulverized, mixed, and fed into a rotary kiln maintaining temperatures between 1100-1800°C.
2. Decomposition: At 1100°C, limestone decomposes to quicklime

CaCO₃ → [1100°C] CaO + CO₂↑

1. Synthesis Reactions (1400-1500°C): Calcium oxide reacts with silica, alumina, and iron oxide present in clay to form silicates and aluminates

• 2CaO + SiO₂ → 2CaO · SiO₂ (Dicalcium silicate)
• 3CaO + SiO₂ → 3CaO · SiO₂ (Tricalcium silicate)
• 3CaO + Al_2O₃ → 3CaO · Al_2O₃ (Tricalcium aluminate)
• 4CaO + Al_2O₃ + Fe_2O₃ → 4CaO · Al_2O₃ · Fe_2O₃ (Tetracalcium alumino ferrite)

1. Clinker Formation: The resulting fused pebble-like mass is called clinker.
2. Grinding with Gypsum: Clinker is cooled, blended with 2-3\% gypsum (CaSO₄ · 2H_2O), and ground into fine cement powder.

Soap molecules are sodium or potassium salts of long-chain fatty acids (RCOOM). When soap is dissolved in water, it ionizes into carboxylate ions (RCOO^-) and metal ions (M^+).

The carboxylate ion (RCOO^-) consists of two parts

1. Hydrocarbon Tail (R): Non-polar, hydrophobic (water-repelling), and lipophilic (attracted to oil/dirt).
2. Carboxylate Head (COO^-): Polar, hydrophilic (water-attracted), and ionic.

Formation of Micelles: When oily dirt is present in water, soap molecules align themselves radially around the oil drop. The hydrophobic hydrocarbon tails stick inside the oil droplet, while the hydrophilic polar heads (COO^-) face outward into the water, forming a spherical structure called a micelle. These micelles suspend the dirt in water as a colloid, allowing it to be easily washed away.