Introduction to chemistry

At the primary school level, you learnt about science as a general subject. In secondary school, you will build upon this knowledge in three branches of science. These are biology, chemistry and physics.

Fig 1.1: Branches of science

The three branches of science above can be applied in other subject areas, such as agriculture and home science.

Primary school covered the basics of these aspects of chemistry:

• Matter and its properties
• Mixtures and their separations
• Conductors and non-conductors
• Drugs and drug abuse

In primary school science, you learnt about matter. You learnt that matter is anything that occupies space and has mass. The heavier the object is, the more mass it has. You also learnt that matter exists in three different states, namely:

1. Solids– e.g. stone, metal, and wood
2. Liquids– e.g. water, kerosene, and petrol
3. Gases– e.g. air

In chemistry, you will study how matter behaves, and how the state of a substance can be changed under certain conditions. For example, liquids and solids cannot be compressed, and thus their volumes cannot be changed by changing the pressure.

Properties of the three states of matter

The three states of matter have the following properties:

• Solids have a definite shape, and a fixed volume.
• Liquids have a fixed volume, but no definite shape. Instead, they take up the shape of the container they are in.
• Gases have no definite shape or volume. They take up all the space of their container.

Liquids and solids visibly fill a container. Once the container is completely full, adding more will cause it to spill over.

Remember, a container is not as empty as it appears. Before a liquid or solid is added to the container, it is usually full of air that we cannot see. The liquid or solid displaces the air in the container when it is added.

Air occupies the space inside the balloon while it is being inflated. It bursts when you continue blowing because the balloon is stretched by the pressure of the air inside it. These experiments show that liquids, solids, and gases occupy space.

You will realise that the tin full of air is lighter than the tin full of other substances like sand or water.

You can therefore conclude that all matter has mass, but some matter (gas) has less mass compared with others (liquid or solid).

You may have separated some mixtures at home or in school recently. Imagine you were tasked with separating a mixture of maize and beans. Which method would you use to achieve this?

You may also have to separate sand from water. How would you do this? How can you get clean water from muddy water?

Maize and beans can be separated by hand-picking.
​Sand can be separated from water by pouring the water out of the container. This method is called decantation.
​Clean water can be obtained from muddy water by running it through filter paper or cloth in a funnel. This method is called filtration.

You will find that some solids allow the bulb to light up, while others do not. This means that only some solids allow electricity to pass through them. The solids that allow electricity to pass through them are known as conductors. Those that don't are called non-conductors. All metals and graphite are conductors. All non-metals, except graphite, are non-conductors.

A drug is any natural or human-made substance that changes the way in which our bodies work. For example, most medicines are drugs. Medicines can be prescribed, or provided 'over the counter'.

Over-the-counter (OTC) drugs

These are drugs which can be bought from a pharmacy or other shops without a doctor’s prescription. The most common OTC drugs include painkillers (such as paracetamol), anti-acids, and a variety of cough syrups.

Prescription drugs

Other medicines can only be obtained with a prescription from a qualified doctor or health worker. These drugs need to be taken according to the doctor's instructions. It is important to avoid overdosing or underdosing on these drugs, as this can lead to serious health problems.

Drug abuse

Drug abuse is the use of a drug for something other than its intended purpose. Over-the-counter drugs such as painkillers, anti-acids, headache tablets, malaria tablets, and sleeping pills can easily be abused. Always be careful when using these drugs.

Other commonly abused drugs, which are taken for various reasons, include alcohol, tobacco, bhang, miraa (khat), heroin, cocaine, shisha, LSD, morphine, Mandrax, and many others. These drugs are often used to give a false feeling of well-being. They have bad side effects, and can be very damaging to one’s health, or even be lethal. This is why it is illegal in this country to possess, use, or sell illegal drugs.

Drug dependence

Drug dependency comes from abusing substances that are addictive, making the user physically uncomfortable when they do not use them. These include alcohol, tobacco, bhang, miraa (khat), heroin, cocaine, and many others.

Prevention of drug abuse

You can prevent drug abuse by:

• following instructions for taking medicinal drugs.
• never taking illegal drugs.
• keeping away from drug sellers and users that encourage it.
• educating yourself about mental health, and taking care of yourself in a safe and healthy way. This will help you live a fulfilling life where drug abuse isn't a last resort.
• ask for help from your support group or professionals when you feel the need to abuse drugs.