Chemicals – JSS2 Basic Science Lesson Note (Third Term)

A chemical is a substance made of chemical elements, or a substance produced or used in a chemical process.

Behavioural objectives

By the end of the lesson, students should be able to:

1. define a chemical;
2. state the ways in which chemicals can be classified;
3. name the classes of chemicals based on use and give examples of each;
4. state the classes of drugs based on their origin;
5. classify chemicals as highly hazardous, moderately hazardous or non-hazardous.

What is a chemical?

A chemical is any substance made of elements, or any substance made or used in a chemical process.

• Element: a simple substance that cannot be broken into simpler substances, such as sodium, nitrogen and iodine.
• Compound: a substance made when elements join chemically, such as water and carbon dioxide.
• Everyday chemicals: soap, salt, medicines, fertiliser, methylated spirit and cooking gas.

How are chemicals classified?

Chemicals are classified by grouping together those with similar features.

What are the classes of chemicals based on use?

There are five classes of chemicals based on use: pharmaceutical and cosmetic, nuclear, agrochemicals, industrial and laboratory chemicals.

What are pharmaceutical and cosmetic chemicals?

Pharmaceutical chemicals are drugs used to prevent, treat or cure disease or to change how the body works.

• Cosmetic chemicals: products used to clean or improve the look of the body, such as body creams, perfumes, lipsticks and shampoo.

How are drugs classified by origin?

Drugs are classified into five groups by where they come from: natural, partly natural and partly chemical, wholly chemical, animal and microbial.

• Natural origin: drugs from herbs, plants or minerals. Some come from the sea (marine origin).
• Chemical as well as natural origin: drugs made by partial herbal and partial chemical synthesis, for example steroidal drugs.
• Chemical synthesis: drugs made wholly in the laboratory or factory by chemical reactions.
• Animal origin: drugs got from animals, for example hormones and enzymes.
• Microbial origin: drugs got from micro-organisms, for example antibiotics.

What are nuclear chemicals?

Nuclear chemicals are radioactive materials, which give off radiation as their atoms break down.

• Definition by activity: a radioactive material is one with a specific activity greater than 70 becquerel (Bq) per gram.
• Fission in a power plant: a controlled fission reaction gives enough energy to supply electricity to large cities.
• Fusion in the sun: the fusion reaction in the sun gives the light and heat that living organisms on Earth need to survive.
• Fission in a bomb: an uncontrolled fission reaction gives the destructive force of a nuclear bomb.

What are agrochemicals?

Agrochemicals (or agrichemicals) are chemicals used in farming, most often pesticides.

• Insecticides: kill insects.
• Herbicides: kill weeds.
• Fungicides: kill fungi.
• Nematicides: kill nematodes (tiny roundworms in soil).
• Other agrochemicals: synthetic fertilisers, hormones and other chemical growth agents, and concentrated stores of raw animal manure.

What are industrial chemicals?

Industrial chemicals are chemicals used in factories to make goods, and such factories are called chemical-based industries.

• Dyes: colour cloth and other materials.
• Iodine solutions: used to treat wounds.
• Methylated spirit: used as a solvent and fuel.
• Soaps and detergents: used for washing.
• Shampoo and cosmetics: used for body care.

What are laboratory chemicals?

Laboratory chemicals are chemicals used in school and research laboratories for experiments and tests.

• Sodium hydroxide: a strong base.
• Potassium hydroxide: a strong base.
• Hydrochloric acid: a strong acid.
• Tetraoxosulphate VI acid: a strong acid, also called sulphuric acid.
• Sodium trioxocarbonate IV: a salt, also called sodium carbonate.
• Ethanol: an alcohol used as a solvent.

What are the classes of chemicals based on hazardous nature?

There are three classes based on hazard: highly hazardous and toxic, moderately hazardous and toxic, and non-hazardous and non-toxic.

What are highly hazardous and toxic chemicals?

Highly hazardous chemicals can explode, catch fire easily or poison people, so they need the greatest care.

• Explosive chemicals: picric acid, 2,4-dinitrophenol and organic azides.
• Toxic chemicals: chloroform, chromic acid and phenol.
• Rapidly burning chemicals: acetonitrile, methanol, acetone and acetaldehyde.
• Easily ignited metal: sodium.

What are moderately hazardous and toxic chemicals?

Moderately hazardous chemicals can harm the skin, eyes or body if handled carelessly.

• Strong bases: sodium hydroxide and potassium hydroxide.
• Acids: hydrochloric acid, sulphuric acid, boric acid, nitric acid, organic acids and oxidising acids.
• Non-metal: bromine.

What are non-hazardous and non-toxic chemicals?

Non-hazardous chemicals cause no serious harm when used in the normal way.

• Nitrogen: the main gas in air.
• Carbon dioxide: the gas plants use for photosynthesis.

How should chemicals be handled safely?

Safe handling means following simple rules every time a chemical is used.

1. Read the label before using any chemical.
2. Wear gloves, goggles and a lab coat when told to.
3. Never taste or smell an unknown chemical directly.
4. Keep flammable chemicals away from flames and heat.
5. Store chemicals in closed, labelled containers away from children.
6. Wash your hands after using chemicals.

Evaluation

1. What is a chemical?
2. State four ways in which chemicals can be classified.
3. List the classes of chemicals based on use and give one example of each.
4. Name the five classes of drugs based on origin.
5. Give two examples each of highly hazardous and moderately hazardous chemicals.

Assignment

Draw a table with two columns, “Class” and “Examples”. Fill it with two laboratory chemicals, two agrochemicals, two non-hazardous chemicals, one drug of animal origin and one drug of microbial origin.