Here are two simple experiments to help children understand the chemical reaction triggered when liquid soap and food coloring are added to milk, and the science behind air pressure – K.P. Malini

Swirling colours

Materials

• White plate

• Food colouring (as desired)

• Water

• Plastic bowls (as many as the number of colours)

• Milk

• Dish-washing liquid

• Ear buds

Procedure

• Fill a bowl with water. Add some food colouring to it and mix to make a solution.

• Repeat the procedure to make solutions of all the food colours.

• Pour sufficient amount of milk onto a white plate.

• Put a drop of food colour solution in the centre of the milk. Now put a drop of each of the color solutions.

• Take an ear bud and dip it in the centre of the colours. Observe what happens to the colours.

• Now, dip an ear bud in the dish washing liquid.

• Dip the soapy end of the bud in the centre of the colours.

• As soon as the ear bud touches the surface of the milk, you will observe a rush of changing colours which start swirling around in the plate and move towards the edge of the plate.

The science behind it

This experiment helps children understand the components of milk. Milk mainly consists of water, fat, proteins, lactose and minerals. Proteins and fat are very sensitive and react strongly when anything is added to the milk.

When the dish washing liquid dipped ear bud is added to the milk, it triggers a chemical reaction. The soap combines with the fat and pushes out the water in the milk. When the water moves out, it carries the food colouring with it.

This is the cause of different colour patterns swirling on the surface of the milk.

Drinking Candles

Materials

• Green food colouring

• White candles with flat bottom (as many as needed)

• Gas lighter

• Water

• White plate

• Mixing spoons

• Tall transparent glass

• Measuring cylinder

Procedure

• Measure 100 ml of water in the measuring cylinder. Pour it onto a white plate.

• Add few drops of green food colouring to it.

• Place the candle in the centre of the plate.

• Light the candle using a gas lighter (adult supervision is required)

• Take a tall transparent glass which is bigger than the candle and gently cover the candle with it. Care should be taken that there should be at least one inch space between the candle wick and glass bottom when it is placed over the burning candle.

• You will notice that the flame goes off and the candle slowly starts drinking up the water.

• Now try this out with two or more candles.

• You will observe that more water gets inside the glass and the level rises.

The science behind it

This experiment helps children understand the scientific concept of air pressure. Air is all around us and exerts pressure or ‘push’ on us and all other objects. When the candle burns inside the glass, the air inside the glass warms and expands, as hot air occupies more space than cool air. The air pressure inside the glass increases compared to the air pressure outside. To restore balance, some of the high pressure air tries to move outwards.

The candle stops burning when the oxygen inside the glass is used up and the air cools down. Thus, the air pressure inside the glass is now less than the air pressure outside. Again, to restore balance, the air outside tries to move inside of the glass. While doing so, it pushes water into the glass. The water level keeps rising till the air pressure inside and outside becomes equal.