Class 7 Unit-8 (Materials used in Daily Life)

 

Unit-8 (Materials used in Daily Life)

Acids

The compounds which have sour taste are called acids. 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.

 

Bases (Alkali)

The compounds which have bitter taste are called bases. 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.

 

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.

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.

 

Metals

• Metals are materials that are usually hard, shiny, and strong.
• They are good conductors of heat and electricity.
• Most metals can be bent, hammered, or stretched into shapes.
• Examples: iron, copper, gold, silver, aluminum.
• Uses of metals include making utensils, wires, tools, machines, and buildings.

 

Iron (Fe)

Iron is a metal that is very useful in daily life. It is strong, hard, and widely used in construction and manufacturing.

Physical Properties:

1. Iron is silvery-gray and shiny when freshly cut.
2. It is strong, hard, and malleable, so it can be shaped into different forms.
3. It is a good conductor of heat and electricity.

Uses of Iron:

1. Used in making buildings, bridges, and vehicles.
2. Used to make tools, machinery, and household utensils.
3. Used in alloys like steel and cast iron.

 

Aluminium (Al)

Aluminium is a lightweight metal that is silver-white in color. It is soft, malleable, and does not rust easily.

Physical Properties:

1. Aluminium is silvery-white and shiny.
2. It is lightweight, soft, and malleable, so it can be shaped into thin sheets.
3. It is a good conductor of electricity but less than copper.

Uses of Aluminium:

1. Used to make cooking utensils, foil, and beverage cans.
2. Used in aircraft, vehicles, and electrical cables.
3. Used in construction, packaging, and kitchen appliances.

 

Zinc (Zn)
Zinc is a metal that is bluish-white in color and is found in the Earth’s crust. It is an important metal used in many industries.

Physical Properties:

1. Zinc is hard and brittle at room temperature but becomes malleable when heated.
2. It has a shiny, bluish-silver appearance.
3. It is moderately reactive and conducts electricity.

Uses of Zinc:

1. Used for galvanizing iron and steel to prevent rusting.
2. Used in making batteries and alloys like brass.
3. Used in the production of paints, cosmetics, and medicines.

 

Copper (Cu)

Copper is a reddish-brown metal that is very useful in daily life. It is soft, malleable, and a good conductor of heat and electricity.

Physical Properties:

1. Copper has a shiny reddish-brown color.
2. It is soft, ductile, and malleable, so it can be stretched into wires.
3. It is a good conductor of heat and electricity.

Uses of Copper:

1. Used to make wires, electrical cables, and motors.
2. Used in making coins, utensils, and pipes.
3. Used in alloys like brass and bronze.

 

Silver (Ag)

Silver is a precious metal that is shiny and white in color. It is soft, malleable, and one of the best conductors of electricity.

Physical Properties:

1. Silver has a shiny white metallic appearance.
2. It is soft, malleable, and ductile, so it can be made into thin sheets and wires.
3. It is an excellent conductor of heat and electricity.

Uses of Silver:

1. Used to make jewelry, coins, and utensils.
2. Used in electrical contacts, batteries, and mirrors.
3. Used in photography and medicines.

 

Gold (Au)

Gold is a precious yellow metal that has been used by humans for thousands of years. It is soft, shiny, and does not rust or tarnish easily.

Physical Properties:

1. Gold has a bright yellow metallic color.
2. It is soft, malleable, and ductile, so it can be made into thin sheets or wires.
3. It is a good conductor of electricity.

Uses of Gold:

1. Used in jewelry, coins, and ornaments.
2. Used in electronics and dental work.
3. Used as a standard for currency and in awards.

 

Sulphur (S)

Sulphur is a non-metal that is yellow in color and has a distinct smell. It is found naturally near volcanoes and in minerals.

Physical Properties:

1. Sulphur is yellow and brittle.
2. It is solid at room temperature and does not conduct electricity.
3. It melts easily when heated and has a characteristic smell when burned.

Uses of Sulphur:

1. Used to make matches, gunpowder, and fireworks.
2. Used in the production of sulfuric acid for fertilizers and chemicals.
3. Used in medicine, rubber, and insecticides.

 

 

Non-metals

• Non-metals are materials that are usually soft, dull, and brittle (break easily).
• They do not conduct heat and electricity well.
• Many non-metals exist as gases or soft solids.
• Examples: carbon, sulfur, oxygen, nitrogen.
• Uses of non-metals include making fertilizers, medicines, rubber, and fuels.

 

Iodine (I)

Iodine is a non-metal that is dark gray or purple-black in color. It is essential for the human body in small amounts.

Physical Properties:

1. Iodine is solid at room temperature and has a metallic luster.
2. It sublimes on heating, turning directly into a purple vapor.
3. It is brittle and does not conduct electricity.

Uses of Iodine:

1. Used in antiseptic solutions like tincture of iodine.
2. Added to salt (iodized salt) to prevent iodine deficiency.
3. Used in medicine, photography, and dyes.