Water drop art

Student Sheet

In this practical I will be:

• Carrying out and observing the results of the practical.
• Reporting my findings using evidence from the practical.
• Drawing a conclusion of what happens when water is dropped onto wax.

Introduction:

You are working late in your studio, painting by candle light, it has started to rain. You see that rain water has fallen on some melted candle wax and that something peculiar has happened. Like all good science-artists, you decide to investigate further…

Equipment:

• 1 large piece of waxed paper
• 1 wooden toothpick or wooden splint
• Red, green, yellow and blue diluted food colouring in small bottles
• Water in a small bottle
• 5 pipettes or eye droppers for the colourings and water
• Paper towels
• Disposable plastic gloves

Wear disposable plastic gloves

Method:

1. Take the waxed paper and lay it flat on the table.
2. Using a pipette or eye dropper suck up a small quantity of one of the food colourings.
3. Put some scattered drops of the food colouring onto the surface of the wax paper.
4. Repeat steps 2 and 3 with another colour.
   • What do you see happen to the colours on the wax?
5. Record what you see by drawing a picture, taking a photograph or writing a sentence.
6. Now take a toothpick or splint. Dip one end into water hold it there for a few seconds.
7. Remove the splint or toothpick from the water.
8. Dry it on a paper towel.
9. Place the wet end of the splint or toothpick close to, but not touching, one of the coloured droplets on the waxed paper. Watch carefully.
   • What happens?
10. Record what you see by drawing a picture, taking a photograph or writing a sentence.

Going Further:

Now use the effect to create a picture or design.

Chemistry:

The molecules of wax push away from the water molecules in the coloured drop. The wax molecules pull towards each other to form a surface the water molecules cannot link to. The water forms a coloured bead. When the wet toothpick or splint is brought close to the coloured bead it is drawn to the toothpick or splint. This is because the water molecules on the wood attract the water molecules in the coloured bead. This attraction is known as cohesion. If there is attraction between two substances that are not the same it is known as adhesion.

Wax and water do not mix. Oil and water do not mix either. This is because wax and oil are made up of non-polar molecules. Water molecules are polar in nature; they are electrically charged with a positive and negative end to the molecule. This means that water molecules attract each other the positive attracts the negative, but they do not attract non-polar molecules, which are not charged.

Teacher and Technician Sheet

In this practical students will:

• Carry out and observe the results of the practical.
• Report their findings using evidence from the practical.
• Draw a conclusion of what happens when water is dropped onto wax.

Introduction for teachers: 

Wax is a solid and is related to oil. So does it act like oil does when placed in water?

This investigation or art activity allows young children to investigate the effects of mixing waxes with water, but in this activity the water is coloured with food colouring.

Curriculum range:

Lower primary age but can be used with younger secondary age students to investigate materials: links with:

• reporting on findings from enquiries, including oral and written explanations, displays or presentations of results and conclusions;
• using straightforward scientific evidence to answer questions or to support their findings;
• compare and group together everyday materials on the basis of their properties;
• know that some materials will mix, while others will not; 
• build a more systematic understanding of materials by exploring and comparing the properties of a broad range of materials

Going further:

Students could use the effect to create a picture or design.

For older Primary they could move on to make oil and water emulsion see P008.

Hazard warnings:

There are no hazards with this investigation but there is a warning that some food colourings can stain the skin. To prevent this it is advisable to give the children plastic gloves to wear.

It can also be cheaper to dilute the colourings by dropping 10 drops of colour into 20 cm³ of water.

Equipment:

Per group

• 1 large piece of waxed paper 
• 1 wooden toothpick, wooden splint (or spent match)
• Red, green, yellow and blue diluted food colouring in small bottles or 1 % diluted food colourings in stoppered test tubes
• Water in a small bottle
• 5 pipettes or eye droppers for the colourings and water
• Paper towels
• Disposable plastic gloves

Technical notes:

Sandwich wrap or greaseproof paper can be used for the waxed paper and the effect of the attraction of the molecules. However, it‘s not as good visually as using a white background. 

White laminating pouches can be used to good effect. 

Some food colourings (a natural red in this case) may not leave any colouring on the paper

Food colouring solutions can also be prepared from solid powders if available. Make up a 1% solution of each colour (for example, 0.5 g in 50 cm³ distilled water) 

Sets of food colours in powder form can be purchased from school suppliers and prepared to a solution before use. These will be more economical to buy overall as a lot of solution can be produced from the solid.

Students may have to touch the coloured droplet for this to work or leave the toothpick/spill wetter for the water molecules to attract.

Results:

This is an easy experiment to set up and use. Students are encouraged to observe closely any differences between the droplets and they should be able to observe the attraction of the molecules.

It can be observed that the different food colouring droplets may sit on the paper in different ways.

They will also be left with an attractive design on paper at the end of the experiment.