ICSE Class 7 Chemistry Chapter 8 Wastes

Chapter 8: Wastes

In This Chapter You Will Learn

Some common wastes

Classification of wastes

Recycling waste

What can we do to minimise the harmful effects of plastics.

Introduction

Materials which are discarded by us as useless and unwanted are known as wastes. Wastes include solid, liquid and gaseous wastes. But in this chapter we will discuss about solid as well as liquid wastes and the ways of their proper disposal. You will also study about some common waste materials which can be reused and recycled.

8.1 Some Common Wastes

A lot of wastes are produced in every household. Can you remember the types of wastes generated in your home everyday ? Write the wastes generated in your home in the following columns.

Solid wastes

Solid wastes includes the following :

Food wastes - Food wastes include fruit and vegetable peels, left over food, residues of meat, fish, etc. These wastes are generated in homes, restaurant and hotels.

Ash - Ash is produced from burning of wood, coal, coke, etc. Ash is produced mainly in factories, thermal power plants, iron and steel industries.

Rubbish - Paper, plastics, rubber, wood, glass, metallic wastes, polythene bags, cardboard, etc. are called rubbish. These wastes are generated from homes industries, offices, schools, etc.

Liquid wastes

Liquid wastes include wastes discharged from kitchen and bathrooms which contain soap, oil, detergent, human excreta. Besides, a large amount of liquid wastes or effluents is also discharged from industries which contain chemicals, metals wastes.

Gaseous wastes

Harmful gases, smoke and metal particulate come in this category. These wastes are produced by motor vehicles, industries and thermal power plants.

Teacher's Note

Help students identify different types of waste they generate at home daily, making them aware of the sources and composition of household waste.

8.2 Classification Of Waste

1. Biodegradable waste - This type of waste can be broken down into similar substances by the natural action of micro-organisms and thus disappear into the environment.

This includes paper, wheat, biogas, cattle dung, leather, vegetable waste, rice husk, tea leaves, wool, silk, domestic waste, etc.

2. Non-biodegradable waste - Type of waste which cannot be broken down into non-toxic substance by action of micro-organisms. This includes plastic, DDT, glass bottle, aluminium foil, pesticides, etc.

Teacher's Note

Use examples from the local environment to help students understand which wastes decompose naturally and which persist in the environment.

8.3 Recycling Wastes

Of all the components of garbage, only a few, such as metal wastes, glass, paper, certain plastics can be recycled by simple processes.

Recycling conserves not only the non-renewable resources but some renewable resources also.

For example, recycling of paper waste saves trees.

Recycling of metals, glass, etc. saves energy and natural resources.

For example, recycling of metal wastes saves energy used for extracting metals from their ores.

Things which can be recycled are

Empty toothpaste tubes (of aluminium), newspaper waste, electric bulb, empty oil tin, empty glass bottles, PVC shoes, etc.

Recycling of paper - Only the paper used in newspapers, magazines, books, notebooks, etc. can be recycled.

Activity 1

Make recycled paper at home - Make recycled paper at home, collect the paper from old books, newspaper. Tear out all the paper into small pieces and put them into a bucket overnight. Remove the extra water make a paste of paper by pounding it. Spread this pulp on a fine wire mesh and press it to squeeze out the excess water. Move a roller over the pulp to remove extra amount of water and put some weight on it. Leave the pulp for drying for several hours. After drying your hand made recycled paper is ready.

Teacher's Note

Conducting this hands-on activity helps students directly experience the recycling process and understand the value of reusing paper materials.

8.4 Plastic - A Boon Or A Curse

We are living in the plastic age. Plastics are versatile materials for use in our daily life and industry. Plastics are light in weight and are not attacked by moisture and micro-organisms. Plastics last longer.

Plastics can be given any colour and shape of your choice. Plastics are not affected by soil, water, air and micro-organisms. Thus, plastics are non-biodegradable and cause many environmental problems.

8.5 What Can We Do To Minimise The Harmful Effects Of Plastics

(1) Use plastic bags to the minimum. If possible reuse the plastic bags.

(2) Ask the shopkeeper to use paper bags.

(3) Carry a cloth or a jute bag while going out to the market for shopping.

(4) Do not store eatables in plastics bags.

(5) Do not throw used plastic bags here and there. Empty plastic bags choke the drainage system.

(6) Never burn plastic waste. Burning plastics give off toxic gases.

(7) Do not put the domestic garbage into plastic bags while disposing it into the garbage dump.

Teacher's Note

Encourage students to adopt these habits in their daily life and discuss the long-term environmental benefits of reducing plastic consumption.

Objective Type Questions

1. Answer the following questions.

(a) Define wastes.

(b) Write two differences between biodegradable and non-biodegradable waste.

(c) How can you recycle paper ?

(d) Why should we reduce the usage of plastics ?

2. Write true or false for the following statements:

(a) Recycling of waste materials help in saving space and to make old products.

(b) Paper waste, leaves, food waste and domestic waste can be recycled

(c) Polythene bags are very dangerous for the environment

(d) Gaseous wastes are generated mainly from motor vehicles and factories

Multiple Choice Questions

1. Which of the following is not a domestic waste ?

(a) food waste (b) edible oil

(c) paper (d) chemicals

2. Which of the following is not a biodegradable waste ?

(a) peels of vegetables (b) clothes

(c) polythene bags (d) left over food

3. Which of the following cannot be recycled ?

(a) wood (b) iron

(c) glass (d) plastic

4. Which of the following is biodegradable ?

(a) mercury (b) glass

(c) cotton (d) iron

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