General Science Notes Chapter 15 Class 7 Maharashtra Board

Notes For All Chapters – General Science Class 7

Materials we Use

1. Introduction

• We use different materials in our daily life, such as soap, detergents, toothpaste, cement, and alloys.
• These materials help in cleaning, construction, and daily activities.
• Some materials are natural, while others are man-made (synthetic).

2. Soap and Detergents

(A) Soap

• Soap is made from natural fats and oils mixed with sodium hydroxide or potassium hydroxide.
• It is used for cleaning the body and clothes.

✔ Ingredients in Soap:

• Fatty acids – Help remove dirt.
• Glycerin – Keeps skin soft.
• Perfume and color – Give fragrance and appearance.

✔ Types of Soap:

1. Bath Soap – Soft and mild, used for the skin.
2. Washing Soap – Harder, used for clothes and utensils.

✔ Disadvantages of Soap:

• Does not work well in hard water.
• Produces scum, making washing difficult.

(B) Detergents

• Detergents are synthetic cleaning agents made from petrochemicals.
• They work in both hard and soft water.

✔ Advantages of Detergents:

• Work in hard water.
• Produce more foam and remove oil and grease easily.

✔ Disadvantages of Detergents:

• Some harm aquatic life when released into water bodies.
• Can cause skin irritation.

✔ Uses of Detergents:

• Washing clothes, dishes, and surfaces.
• Used in shampoos, liquid soaps, and cleaning powders.

3. Toothpaste and Dental Hygiene

• Toothpaste helps in cleaning and protecting teeth from decay.

✔ Main Ingredients in Toothpaste:

• Fluoride – Prevents cavities and strengthens teeth.
• Calcium carbonate – Removes plaque and dirt.
• Sweeteners and flavoring agents – Improve taste.

✔ Why is Fluoride Important?

• It makes teeth stronger and resistant to decay.

✔ Harmful Effects of Tobacco Masheri:

• Damages tooth enamel.
• Can cause gum diseases.

4. Cement and Its Uses

✔ What is Cement?

• Cement is a binding material used in construction.
• It is made from lime, silica, alumina, iron oxide, and gypsum.

✔ Uses of Cement:

• Building houses, bridges, and roads.
• Making concrete and plaster.

✔ Types of Cement:

• Portland Cement – Most commonly used for construction.
• White Cement – Used for decoration.

✔ What Happens if Cement is Mixed with Too Much Water?

• It becomes weak and cracks easily.

✔ Why is Cement Important in Concrete?

• It holds bricks, stones, and sand together, making structures strong.

5. Alloys – Mixtures of Metals

✔ What is an Alloy?

• An alloy is a mixture of two or more metals to improve strength and durability.

✔ Examples of Alloys and Their Uses:

✔ Advantages of Alloys:

• Stronger and more durable than pure metals.
• Resistant to rust and corrosion.

6. Rusting and Its Prevention

✔ What is Rusting?

• Rusting occurs when iron reacts with water and oxygen, forming a brownish iron oxide layer.

✔ How to Prevent Rusting?

1. Painting and oiling – Protects metal from air and water.
2. Galvanization – Coating iron with zinc to prevent rust.
3. Using stainless steel – Does not rust easily.

7. Cleaning and Hygiene in Daily Life

✔ Importance of Cleaning Materials:

• Helps remove germs and dirt from the body, clothes, and surroundings.
• Prevents diseases and keeps us healthy.

✔ Examples of Cleaning Materials:

• Soap and shampoo – For body and hair.
• Detergents – For washing clothes and dishes.
• Toothpaste – For cleaning teeth.