Class 8 Science Chapter 10 Materials of Daily Use

 Introduction Materials of Daily Use

• Materials of daily use include acids, bases, and salts which are widely used in our homes, industries, and laboratories.
• They have different properties, applications, and roles in chemical reactions.
• Caution → We should not taste or touch all substances directly as they may be harmful, corrosive, or poisonous.

Acids

• Definition: Substances that produce hydrogen ions (H⁺/protons) in aqueous solution.
• Taste: Sour.
• Examples: Hydrochloric acid (HCl), Sulphuric acid (H₂SO₄), Citric acid.

Bases

• Definition: Substances that produce hydroxyl ions (OH⁻) in aqueous solution.
• Taste: Bitter; feel soapy.
• Examples: Sodium hydroxide (NaOH), Potassium hydroxide (KOH).

Salts

• Definition: Substances formed by the neutralisation reaction of acid and base.
• Examples: Sodium chloride (NaCl), Copper sulphate (CuSO₄).

 Indicator

• Definition: A substance that changes colour in the presence of acids and bases, helping to identify their nature.
• Types: Natural (litmus, red cabbage juice), Synthetic (methyl orange, phenolphthalein).

Table: Colour of Indicators in Acidic, Basic and Neutral Solutions

Indicator	Acidic Solution	Basic Solution	Neutral Solution
Red litmus paper	Remains red	Turns blue	Red
Blue litmus paper	Turns red	Remains blue	Blue
Methyl orange	Red	Yellow	Orange
Phenolphthalein	Colourless	Pink	Colourless
Red cabbage juice	Red/pink	Green/blue	Purple

Acids

Definition

• Substances that release H⁺ ions in aqueous solution and turn blue litmus red.

Types of Acids

1. Mineral Acids
   • Definition: Strong inorganic acids prepared from minerals.
   • Examples: Hydrochloric acid (HCl), Sulphuric acid (H₂SO₄), Nitric acid (HNO₃).
2. Organic Acids
   • Definition: Weak acids found naturally in plants/animals.
   • Examples: Citric acid (citrus fruits), Acetic acid (vinegar), Lactic acid (milk).

Applications of Acids in Daily Life

1. Citric acid in food preservation.
2. Sulphuric acid in car batteries.
3. Acetic acid in vinegar for cooking.
4. Hydrochloric acid in digestion in the stomach.

 Physical Properties of Acids

1. Sour in taste.
2. Turn blue litmus red.
3. Conduct electricity in aqueous solution.
4. Corrosive in nature (can damage skin/metals).

Chemical Properties of Acids (with examples)

1. Reaction with Metals → Produces salt + hydrogen gas.
   • Zn + 2HCl → ZnCl₂ + H₂↑
2. Reaction with Bases (Neutralisation) → Produces salt + water.
   • HCl + NaOH → NaCl + H₂O
3. Reaction with Carbonates → Produces salt + water + carbon dioxide.
   • CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂↑
4. Reaction with Metal Oxides → Produces salt + water.
   • H₂SO₄ + CuO → CuSO₄ + H₂O

 Uses of Acids

Inorganic Acids:

• HCl → Used in cleaning metal surfaces, digestive acid in stomach.
• H₂SO₄ → Used in car batteries, manufacture of fertilizers, detergents.
• HNO₃ → Used in making explosives, fertilizers.
• H₃PO₄ → Used in soft drinks, fertilizers.

Organic Acids:

• Citric acid → Food preservative, sour taste in citrus fruits.
• Acetic acid → Vinegar, used in pickling.
• Lactic acid → Found in curd, used in food industry.
• Tartaric acid → Used in baking powder.

Bases

Definition

• Substances that produce OH⁻ ions in water and turn red litmus blue.
• Examples: NaOH, KOH, NH₄OH.

 Strong Bases and Weak Bases

• Strong Bases
  • Definition: Completely dissociate into OH⁻ ions in solution.
  • Examples: NaOH, KOH.
  • Uses: Soap-making, neutralising acids.
• Weak Bases
  • Definition: Partially dissociate into OH⁻ ions.
  • Examples: NH₄OH, Mg(OH)₂.
  • Uses: Medicine (antacids), laboratory uses.

 Physical Properties of Bases

1. Bitter in taste.
2. Soapy/slippery to touch.
3. Turn red litmus blue.
4. Good conductors of electricity in aqueous solution.
5. Corrosive in strong concentrations.

Chemical Properties of Bases (with equations)

1. Reaction with Acids (Neutralisation)
   • NaOH + HCl → NaCl + H₂O
2. Reaction with Non-metal Oxides
   • 2NaOH + CO₂ → Na₂CO₃ + H₂O
3. Reaction with Ammonium Salts (Releases Ammonia Gas)
   • NaOH + NH₄Cl → NaCl + H₂O + NH₃↑

 Uses of Bases/Alkalis

• Sodium Hydroxide (NaOH)
  • Used in soap-making.
  • Paper industry.
• Potassium Hydroxide (KOH)
  • Used in making liquid soaps.
  • Used in alkaline batteries.
• Ammonium Hydroxide (NH₄OH)
  • Used as a cleaning agent.
  • Used in fertilizers.
• Calcium Hydroxide (Ca(OH)₂)
  • Used in whitewashing walls.
  • Used in neutralising acidic soil.
• Magnesium Hydroxide (Mg(OH)₂)
  • Used as antacid (milk of magnesia).
  • Used in wastewater treatment.

Salts

Definition

• Salts are ionic compounds formed by neutralization of acids and bases.

Types of Salts

1. Neutral Salts
   • Formed when strong acid reacts with strong base.
   • Example: NaCl.
   • Neutral because solution is neither acidic nor basic.
2. Acidic Salts
   • Formed when strong acid reacts with weak base.
   • Example: NH₄Cl.
   • Acidic due to incomplete neutralization.
3. Basic Salts
   • Formed when weak acid reacts with strong base.
   • Example: Na₂CO₃.
   • Basic due to leftover OH⁻ ions.

Physical Properties of Salts

1. Crystalline solids.
2. Soluble in water (mostly).
3. Have definite melting/boiling point.
4. Conduct electricity in solution.
5. Taste may be salty, bitter, or sour depending on type.

Chemical Properties of Salts

a. Ionization in Water

• NaCl → Na⁺ + Cl⁻

b. Reaction with Acids

• Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂↑

c. Reaction with Bases

• NH₄Cl + NaOH → NaCl + NH₃↑ + H₂O

d. Reaction with Active Metals

• Zn + CuSO₄ → ZnSO₄ + Cu

Uses of Salts

• Sodium Chloride (NaCl) → Food seasoning, preservative.
• Sodium Carbonate (Na₂CO₃) → Washing soda, softening hard water.
• Sodium Bicarbonate (NaHCO₃) → Baking soda, antacid.
• Copper Sulphate (CuSO₄) → Fungicide, electroplating, blue vitriol.

 Exam Tip: Always remember → Acid + Base → Salt + Water (Neutralization).
 Use word equations and balanced chemical equations wherever possible in answers

 Comparison: Acids vs Bases vs Salts

Feature	Acids	Bases/Alkalis	Salts
Definition	Substances producing H⁺ ions in solution	Substances producing OH⁻ ions in solution	Formed by neutralisation of acid & base
Taste	Sour	Bitter, soapy	Varies (salty, bitter, etc.)
Litmus test	Blue → Red	Red → Blue	Mostly neutral (no change)
pH range	< 7	> 7	≈ 7 (neutral salts)
Examples	HCl, H₂SO₄, Acetic acid	NaOH, KOH, NH₄OH	NaCl, Na₂CO₃, CuSO₄
Common uses	Batteries, digestion, food industry	Soap-making, antacids, fertilizers	Seasoning, electroplating, detergents

 Interesting Facts

• Litmus is a natural dye obtained from lichens.
• Stomach acid (HCl) has pH ~2, strong enough to dissolve metal nails if left for long.
• Baking powder = Sodium bicarbonate + Tartaric acid → used in fluffy cakes.
• Copper sulphate crystals are blue, but turn white when water of crystallisation is removed.

 Mnemonics/Memory Aids

• Acids turn Blue litmus Red → “Acid makes B to R” (Think: B-R = Break).
• Bases turn Red litmus Blue → “Base makes R to B” (Think: R-B = Reverse).
• Strong Acid + Strong Base = Neutral Salt (NaCl example).

 Summary / Quick Revision

• Acids → Sour, H⁺ producer, corrosive, used in batteries, digestion.
• Bases → Bitter, OH⁻ producer, soapy, used in soap, cleaning, antacids.
• Salts → Neutralisation products, crystalline, wide applications (NaCl, Na₂CO₃, NaHCO₃, CuSO₄).
• Indicators → Litmus, methyl orange, phenolphthalein, red cabbage juice.
• Daily life applications → Preservatives, fertilizers, electroplating, medicines.
• Equations to remember →
  • Acid + Metal → Salt + H₂↑
  • Acid + Base → Salt + H₂O
  • Acid + Carbonate → Salt + H₂O + CO₂↑
  • Base + Ammonium salt → Salt + H₂O + NH₃↑

 Acid Rain

Definition & Overview

• Acid rain → Rainwater mixed with strong mineral acids such as sulphuric acid (H₂SO₄) and nitric acid (HNO₃) formed in the atmosphere.
• Caused by burning of fossil fuels, volcanic eruptions, industries releasing SO₂, NO₂, CO₂.
• pH of acid rain ≈ < 5.6 (normal rainwater has pH ≈ 5.6 due to dissolved CO₂).

 Formation of Acid Rain

1. Formation of sulphuric acid
   • SO₂ (from burning coal, oil, industries) + O₂ → SO₃
   • SO₃ + H₂O → H₂SO₄ (sulphuric acid in rainwater)
2. Formation of nitric acid
   • N₂ + O₂ → NO (in vehicle engines, lightning)
   • NO + O₂ → NO₂
   • NO₂ + H₂O → HNO₃ (nitric acid in rainwater)
3. Acid rain formation
   • Cloud droplets absorb H₂SO₄ and HNO₃ → rain/snow/sleet with acidic pH.

Effects of Acid Rain (4 points)

• Destroys aquatic life → lowers pH of rivers/lakes, kills fish.
• Damages crops & forests → leaches nutrients from soil, harms leaves.
• Corrodes buildings/monuments → dissolves marble (Taj Mahal → “Marble cancer”).
• Affects human health → respiratory problems (asthma, bronchitis).

Control Measures (4 points)

• Reduce fossil fuel use, promote renewable energy.
• Use scrubbers & catalytic converters in industries/vehicles.
• Afforestation (trees absorb CO₂, SO₂, NO₂).
• Awareness & international agreements (e.g., Kyoto Protocol, Paris Agreement).

 Soft Water & Hard Water

a. Soft Water

• Definition → Water that easily forms lather with soap.
• Example → Rainwater, distilled water.
• Why called soft? → No dissolved calcium/magnesium salts.
• Features (3):
  1. Produces lather quickly with little soap.
  2. Does not form scum.
  3. Suitable for washing and laundry.

b. Hard Water

• Definition → Water that does not lather easily with soap but forms scum.
• Example → Well water, river water rich in minerals.
• Why called hard? → Contains dissolved Ca²⁺, Mg²⁺ salts.
• Features (3):
  1. Wastes soap → forms insoluble scum.
  2. Causes scaling in boilers/pipes.
  3. Not good for washing, but healthier to drink (contains minerals).

 Hardness of Water

a. Temporary Hardness

• Caused by calcium & magnesium bicarbonates (Ca(HCO₃)₂, Mg(HCO₃)₂).
• Why called temporary? → Removed by boiling.
• Causes → Scale deposits in kettles and boilers.

Removal Methods:

i. By boiling → Bicarbonates decompose to insoluble carbonates → settle as precipitate.
ii. Clark’s method → Add slaked lime (Ca(OH)₂) → precipitates bicarbonates as insoluble CaCO₃, Mg(OH)₂.

b. Permanent Hardness

• Caused by sulphates, chlorides, nitrates of Ca²⁺, Mg²⁺.
• Why permanent? → Cannot be removed by boiling.
• Causes → Serious boiler scaling, reduces efficiency.

Removal Methods:

i. By washing soda (Na₂CO₃):

• CaSO₄ + Na₂CO₃ → CaCO₃↓ + Na₂SO₄
• Converts soluble salts to insoluble precipitates.

ii. Permutit method (Ion exchange):

• Water passed through sodium zeolite (Na₂Z).
• Ca²⁺, Mg²⁺ ions exchanged with Na⁺ ions.
• Permanent & efficient method for large-scale water softening.

 Alloys (Mixed Metals)

• Alloys → Homogeneous mixtures of two or more metals, or metal + non-metal (like carbon).
• Prepared to improve strength, hardness, resistance, durability compared to pure metals.

 Properties of Alloys (4 points)

1. Harder than parent metals.
2. Resistant to corrosion/rust.
3. Sometimes lighter but stronger.
4. Better appearance (lustre, color).

Some Common Alloys

• Steel → Iron + Carbon (sometimes Ni, Cr).
  • Uses: Construction, tools, vehicles, bridges.
• Brass → Copper + Zinc.
  • Uses: Musical instruments, utensils, decorative items.
• Bronze → Copper + Tin.
  • Uses: Statues, medals, bells, coins (historical).
• Duralumin → Aluminium + Copper + Manganese + Magnesium.
  • Uses: Aircraft, vehicles, machinery (lightweight + strong).

Interesting Facts

• Norway & Canada still face acid rain due to industrial emissions in neighboring countries.
• Soap forms scum in hard water because Ca²⁺ + soap (sodium stearate) → insoluble calcium stearate.
• Bronze Age (historical period) → named after the widespread use of bronze tools.

 Mnemonics

• Temporary hardness → Bicarbonates → Boiling removes. (Think: B = Boil).
• Permanent hardness → Sulphates/Chlorides → Soda/Zeolite removes. (Think: P = Permutit).

Quick Revision

• Acid Rain: Caused by SO₂, NO₂ gases → forms H₂SO₄, HNO₃ → damages environment, monuments, health.
• Soft Water: Easily lathers with soap; Hard Water: Contains Ca²⁺, Mg²⁺, causes scum.
• Temporary Hardness: Due to bicarbonates, removed by boiling/Clark’s method.
• Permanent Hardness: Due to sulphates/chlorides, removed by washing soda/Permutit.
• Alloys: Mixtures of metals → stronger, durable. Examples: Steel, Brass, Bronze, Duralumin.

Also Check Out :- Chapter 1 , chapter 2 , chapter 3 , chapter 4 , chapter 5 , chapter 6 , chapter 7 , chapter 8