Category Chemical World

Chemicals surround us all the time and influence our lives without us even noticing. Here you can see a few more examples of some chemical and physical reactions with everyday chemicals.

Producing gas

Many different chemical reactions produce gas. At home, why not try producing carbon dioxide gas. To do this, mix together vinegar, which is acidic, and baking powder, which is alkaline, in a jar. Make sure the jar is in a sink — watch the bubbles of carbon dioxide erupt over the edge of the jar!

Physical change

Iron filings and sulphur can be mixed together. The iron filings can be easily separated from the mixture as they are attracted by a magnet. This is an example of a physical change. In a physical change, the material changes only its appearance. It is easy to reverse the change because no new substances are formed.

Chemical change

Eggs and bread are mixtures of compounds. When they are heated, new compounds are formed and a chemical reaction has taken place. We cannot undo this change in a simple way. Only complex chemical processes can reverse a chemical change.

How does evaporation work?

Ask an adult to help you boil a solution of salt and water. As the solution is heated, the tiny molecules move more rapidly. The water molecules eventually gain enough energy to fly off as gas. However, there’s not enough energy for the salt to boil, and it is left behind.

People have always used natural chemicals in their daily lives. Vegetable dyes are used to colour wool and cloth or to make paint. Other chemicals from plants have been used as medicines. Originally, drugs such as penicillin were made from moulds grown naturally. Today, most of our medicines are artificially produced.

Scientists have produced chemicals to help farmers. Fertilizers, spread on the fields, make crops plentiful and strong. Pesticides can be used to kill insects that damage crops. Although chemicals are used to improve our lives, many may be harmful too. For this reason, chemicals are developed and tested in laboratories before they are used.

            Pesticides are sprayed on crops to protect them from being eaten by insects.

Red cabbage contains a coloured chemical which acts as an indicator. The blue dye from the cabbage turns pink in acids and green in alkalis. Neutral substances do not make the indicator change colour. Make your own indicator and find out which of the everyday chemicals you have at home are acids or alkalis.

What you need

Red cabbage, a knife, a chopping board, boiling water, 2 bowls, blotting paper, a wooden spoon, clothes pegs, string, milk, soap, lemon juice, bicarbonate of soda and water.

Ask a grown-up to boil some water and chop the cabbage leaves. Put the cabbage leaves in a bowl.

Carefully add the water to the cabbage leaves. Stir the mixture using a wooden spoon. The dye from the cabbage will turn the water blue.

When the solution has cooled, pour the water into another bowl. You don’t need the cabbage leaves anymore.

Dip strips of white blotting paper into the indicator solution. When they are soaked in dye hang them up to dry using string, tied between two points, and some clothes pegs.

Use your indicator paper to test any liquids you may have. (You can also test solids dissolved in water). Just place a few drops of each chemical onto a fresh piece of indicator paper. Try testing chemicals such as soap, milk, lemon juice, and bicarbonate of soda mixed with water. Different substances turn the paper different colours.

Air is a mixture. It contains many gases including nitrogen, oxygen and carbon dioxide. Nitrogen combines with other elements to make compounds called ‘proteins’. Proteins help plants and animals grow, and animals need oxygen to breathe. At the top of a mountain, there is less air than at the bottom. For this reason, mountain climbers sometimes need to take extra oxygen with them.

In sunlight, plants grow by combining carbon dioxide and water to produce more of the chemicals of which they are made. Gases in the air are being used all the time, but they never run out!

The Gas Cycle

We take oxygen from the air, but put back carbon dioxide. Plants take carbon dioxide from the air and, during the day, put back oxygen. Plant and animal bodies contain nitrogen. When they die, this nitrogen returns to the air or soil. Oxygen, carbon dioxide and nitrogen are constantly recycled so we never run out!

            Fighter pilots take their own oxygen supply with them as there is very little air at high altitudes.

            Plants and animals depend on each other to produce the chemicals needed for survival.

 Picture Credit : Google

Crude oil is a thick, black liquid found deep under the Earth’s surface. It was formed millions of years ago from the bodies of tiny animals and plants which lived in the sea. Crude oil is a mixture of many very useful chemicals.

Crude oil is pumped up to the Earth’s surface and is piped to a refinery. Here the different liquids are separated from each other. Some of the liquids, such as petrol and paraffin, can be used as fuels. Others are changed chemically to produce compounds, such as plastics and waxes. Chemicals that come from oil are contained in many of the things we use every day, such as plastic bags and bottles, drain pipes, and some window frames and carpets.

Each liquid chemical boils at a different temperature. The temperature at which it boils is called its ‘boiling point’. When crude oil is heated at the refinery, its temperature slowly rises. The liquid with the lowest boiling point is the first one to boil and form a gas.

This rises upwards, then cools back to a liquid and is collected. As the heating continues, the liquids are separated and collected one by one. The last liquid to be collected is the one with the highest boiling point. This process of separation is called ‘distillation’.

Some chemicals are acids or alkalis. Vinegar, lemon juice and sour milk are all weak acids. They all have a similar sharp, sour taste. Oven cleaner, washing soda and toothpaste are all alkalis. Alkalis taste bitter and feel soapy.

Our stomachs contain hydrochloric acid. This acid kills some of the bacteria in our food and helps us to digest our meals. Too much stomach acid causes indigestion. Medicines used to cure stomach pains are often alkalis. When you mix an alkali with an acid, you make a ‘neutral’ solution — neither acidic nor alkaline. Many plants thrive in a soil which is not very acid, so farmers may add lime to the soil. Lime (an alkali) ‘neutralizes’ acidic soil.

Indicators

An ‘indicator’, such as litmus, is a substance that changes colour when it is mixed with an acid or an alkali.

When litmus paper is dipped into lemon juice, it turns red. Alkaline stomach medicine turns it blue. When the acid and the alkali are mixed, a neutral solution is formed which does not colour the litmus.

Car batteries contain a very strong acid solution. Never touch a car battery with bare fingers.

Farmers and gardeners use an alkali – lime – to neutralize acidic soil before planting.