Class 8 Unit-10 (Materials used in Daily Life)

 

Unit-10 (Materials used in Daily Life)

Acids

The compounds which have sour taste are called acids.

Chemically, acids are compounds which produce H+ (proton) in water.

Examples: Lemon juice, vinegar, hydrochloric acid.

Physical properties of acids

1. Acids have sour taste.

2. Acids turn moist blue litmus to red.

3. Common acids are citric acid (in lemon), acetic acid (in vinegar), and sulfuric acid (in batteries).

4. Acids can burn skin.

 

Chemical Properties of acids:

1. Acids react with bases to form salt and water (neutralization reaction).

2. They react with carbonates to produce carbon dioxide gas.

3. Strong acids can corrode metals and burn skin, so they must be handled carefully.

 

1. Mineral Acids (Inorganic Acids)

Mineral acids are acids that are obtained from minerals and do not contain carbon (except carbonic acid). They are usually strong acids.

Examples:

  • Hydrochloric acid (HCl) – found in stomach; used in industries.
  • Sulfuric acid (H₂SO₄) – used in batteries and fertilizers.
  • Nitric acid (HNO₃) – used in explosives and dyes.

Uses:

  • Used in fertilizers, batteries, and industrial chemicals.
  • Used in cleaning metals and laboratories.

2. Organic Acids
Organic acids are acids that are found in living organisms and contain carbon. They are usually weak acids.

Examples:

  • Citric acid – found in lemons and oranges.
  • Acetic acid (CH₃COOH) – found in vinegar.
  • Lactic acid – found in sour milk.

Uses:

  • Used in food preservation and flavoring.
  • Used in medicines and cosmetics.
  • Used in fermentation and soft drinks.

 

Bases (Alkali)

The compounds which have bitter taste are called bases.

Chemically, bases are compounds which produce OH-(proton) in water.

Examples: Soap, baking soda, lime water.

Physical properties of bases

1. Bases have bitter taste.

2. Bases turn moist red litmus paper blue.

3. Bases react with acids to form salt and water.

4. Some bases are sodium hydroxide, calcium hydroxide, and ammonia.

 

Chemical Properties of bases:

1. Base reacts with acids to form salt and water.

2. Base reacts with ammonium salt to form ammonia gas.

 

Uses of Bases

1. Soap and Detergent Making:
Bases like sodium hydroxide (NaOH) are used to make soaps and cleaning agents.

2. Agriculture:
Bases such as calcium hydroxide (Ca(OH)₂) are used to neutralize acidic soil and make it suitable for crops.

3. Paper and Textile Industry:
Bases are used in the manufacture of paper, textiles, and dyes.

4. Medicines:
Some bases like magnesium hydroxide (Mg(OH)₂) are used as antacids to reduce stomach acidity.

5. Water Treatment:
Bases are used to purify water by removing impurities and hardness.

6. Chemical Industry:
Bases are used in making fertilizers, plastics, and various chemicals.

 

Salts

Salt can be defined as a compound formed by reaction of an acid with a base.

Examples: Sodium carbonate, potassium chloride, copper sulphate, sodium nitrate, etc.

The types of salt:

1. Neutral salt: A salt formed by strong acid and strong base is called neutral salt.

2. Acidic salt:  A salt formed by strong acid and weak base is called acidic salt.

3. Basic salt:  A salt formed by weak acid and strong base is called basic salt.

Physical properties of salts

1. Salt is a substance formed when an acid reacts with a base.

2. Most salts are crystalline solids and soluble in water.

3. Salt is used in cooking, medicines, and industries.

 

Indicators

Substances which impact different colour in acid and base area called acid-base indicators.

 

pH Scale

The pH scale measures how acidic or alkaline a substance is. The scale ranges from 0 to 14. A pH of 7 is neutral. A pH less than 7 is acidic, and a pH greater than 7 is basic. Pure water is neutral, with a pH of 7.0.

 

Acid rain

Acid rain is rainwater that is more acidic than normal due to harmful gases in the air. It is caused when sulfur dioxide (SO₂) and nitrogen oxides (NOâ‚“) mix with rainwater to form sulfuric acid and nitric acid.

Causes of Acid Rain:

1. Burning of fossil fuels like coal, oil, and petrol in factories, power plants, and vehicles.

2. Emission of gases like sulfur dioxide and nitrogen oxides into the atmosphere.

3. Volcanic eruptions and forest fires also release acidic gases.

Effects of Acid Rain:

1. Damages plants and crops by changing soil pH.

2. Corrodes buildings, monuments, and metals.

3. Harms aquatic life in rivers and lakes by lowering water pH.

4. Affects human health indirectly by polluting air and water.

 

Hardness of water

Hardness of water refers to the presence of dissolved salts of calcium and magnesium ions in water. Hard water does not easily form lather with soap and can cause scaling in pipes and appliances.

 

Soft water: Water that produces lather (foam) with soap readily is called soft water.

Hard water: Water that does not produce lather with soap readily is called hard water.

 

Types of Hardness:

1. Temporary Hardness:

o Caused by bicarbonates of calcium and magnesium.

o Can be removed by boiling the water.

2. Permanent Hardness:

o Caused by chlorides and sulfates of calcium and magnesium.

o Cannot be removed by boiling; requires chemical treatment like washing soda.

 

Advantages of Hard Water

1. Source of Minerals:
Hard water contains calcium and magnesium, which are essential for healthy bones and teeth.

2. Good for Drinking:
Drinking moderately hard water may improve heart health and provide necessary minerals for the body.

3. Tastes Better:
Hard water often has a better taste compared to soft water because of dissolved minerals.

4. Beneficial for Plants:
Calcium and magnesium in hard water help plants grow and strengthen their structure.

5. Reduces Heart Disease Risk:
Studies suggest that hard water may help reduce cardiovascular problems due to its mineral content.

 

Disadvantages of Hard Water

1. Forms Scales in Appliances:
Hard water leaves chalky deposits (scale) in boilers, kettles, and pipes, reducing efficiency.

2. Consumes More Soap:
Hard water does not lather easily, so more soap or detergent is needed for washing.

3. Affects Laundry:
Clothes washed in hard water may become stiff and rough.

4. Skin and Hair Problems:
Hard water can cause dry skin, irritation, and rough hair.

5. Clogs Pipes:
Continuous use of hard water can block water pipes due to mineral deposits.

 

Removal of Hardness:

  1. Boiling – removes temporary hardness.
  2. Addition of washing soda (Na₂CO₃) – removes permanent hardness.
  3. Ion-exchange methods – used in water softening plants.

 

Alloys

An alloy is a mixture of two or more metals, or a metal and a non-metal, combined to get better properties than the individual elements.

Examples of Alloys:

1. Steel – Iron + Carbon (stronger than iron).

2. Brass – Copper + Zinc (used in musical instruments).

3. Bronze – Copper + Tin (used in statues and coins).

4. Solder – Lead + Tin (used for joining metals).

5. Duralumin – Aluminium + Copper + Magnesium (used in airplanes).

Characteristics of Alloys

1. Stronger than Pure Metals:
Alloys are usually harder and stronger than the metals they are made from.

2. Resistant to Corrosion:
Many alloys, like stainless steel, do not rust easily.

3. Improved Durability:
Alloys are more durable and long-lasting compared to pure metals.

4. Special Properties:
Alloys can have specific properties such as lightness, flexibility, or heat resistance depending on their composition.

5. Malleability and Ductility Vary:
Alloys are often less malleable or ductile than pure metals, making them suitable for structural uses.

6. Uniform Composition:
Alloys are homogeneous mixtures, meaning the metals and other elements are mixed evenly.

 

1. Brass

Composition: Copper + Zinc
Properties:

·   Yellowish in color and shiny.

·   Harder than copper and resistant to corrosion.

·   Used to make musical instruments, decorative items, coins, and valves.

2. Bronze

Composition: Copper + Tin
Properties:

·   Reddish-brown in color and stronger than copper.

·   Resistant to corrosion and does not rust easily.

·   Used in statues, coins, medals, and machinery parts.

3. Steel

Composition: Iron + Carbon (sometimes other elements)
Properties:

·   Stronger and harder than iron.

·   Can be tempered or stainless to resist rust.

·   Used in construction (bridges, buildings), tools, vehicles, and machinery.

 

Comments

Post a Comment

Popular posts from this blog

Class 8 Unit-2 (Information & Communication Technology)

                                          Chapter-2 Information & Communication Technology  Group 'A' (Multiple Choice Questions) Which of the following are not the tools of information and communication technology? (a) Newspaper ✅             (b) Projectors (c) Television                     (d) Microscope What is the full form of ATM? (a) Automatic transfer machine     (b) Automatic teller machine (c) Automated teller machine ✅ (d) Autograph transfer machine Which of the following statements are incorrect about the precautions to be taken while using ATM? (a) ATM cards and PINs should be kept safe. (b) The PIN should be changed from time to time. (c) It is ...
Read more

Class 6 Unit-2 (Information & Communication Technology)

  Unit-2 Information & Communication Technology   Page No. 31, 32 D. Differentiate between: 1.      Traditional technology and modern technology: Traditional Technology Modern Technology 1.      Based on old methods and local materials 1.      Based on advanced science and innovation 2.      Less efficient and more time-consuming 2.      Highly efficient and time-saving 3.      Requires manual labor 3.      Often automated or machine-based 4.      Example: Grinding spices on stone 4.      Example: Using a mixer grinder   2.      Local skills and modern skills: Local Skills Modern Skills ...
Read more

Class 7 Unit-2 (Information & Communication Technology)

Unit-2 Information & Communication Technology   Page No. 21 and 22   D. Give reasons: Sitting locally and acting globally is possible due to the development of ICT. ICT (Information and Communication Technology) allows people to communicate and access information globally through the internet, video calls, emails, and other tools. This enables people to work or collaborate with others around the world while staying in one place. Cybersecurity is an important aspect of ICT. Cybersecurity protects computers, networks, and data from unauthorized access, attacks, or damage. Without cybersecurity, ICT systems would be vulnerable to hackers, data loss, and cyber crimes.   E. Very short answer type questions: What are data? Data are raw facts and figures that have no meaning on their own. What is information? Information is processed data that has meaning and can be used for decision-mak...
Read more