A Colourful Density Experiment

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October 04, 2024 / DIY / STEM Activities / Chemistry / Ages 6 - 8 / Rainbow In A Tube

Explore the mysteries of colour mixing and density through this simple yet artistic science project!

Age: 6-8
Time: Less than 30 minutes
Mess Level: Messy

Materials Needed:

Food colouring
Water
Salt
Stirring stick
Cups
Test tube or clear bottle
Dropper
Spoon

A light blue surface displays the meticulously arranged components for a Rainbow in a Tube experiment. Five small bottles of coloured liquid, exhibiting varying shades of red, orange, yellow, blue, and purple, are centrally positioned. These are flanked by clear plastic beakers, a larger clear plastic jug of water, a small container of white powder (likely sugar or salt), a measuring spoon, a pipette, and a small stirring stick. The setup is neat and organised, ready for the layering process to create the colourful density column.

Step-by-Step Instructions:

Pour 100ml of water into four separate cups. Add different food colourings to each cup to create purple, blue, yellow, and red coloured water.

Four clear plastic cups, arranged in a row on a pale blue surface, contain layered liquids creating a miniature rainbow effect. From left to right, the cups show layers of purple, blue, yellow, and red liquids, with a thin white layer visible at the top of each. The colours are vibrant and distinct, clearly demonstrating the principle of liquid density. The background is a plain, off-white wall, drawing attention to the colourful cups. The overall impression is of a successful and visually appealing science experiment.

Add 3 spoons of salt to the purple coloured water, 2 spoons to the blue, 1 spoon to the orange, and stir to dissolve. Don't add any salt to the red coloured water.

A hand is adding a small amount of white powder, likely sugar or salt, to a clear plastic cup containing a layered liquid. The cup is one of four arranged in a row on a light blue surface, each cup containing a different coloured liquid, creating a rainbow effect. The colours are vibrant and distinct, showing purple, blue, yellow, and red. The background is a plain, off-white wall. The image shows a step in a density experiment, focusing on the addition of a substance to alter the density of one of the layers.

A hand is adding a small amount of white powder, likely sugar or salt, to a clear plastic cup containing a layered liquid. The cup is one of four arranged in a row on a light blue surface, each cup containing a different coloured liquid, creating a rainbow effect. The colours are vibrant and distinct, showing purple, blue, yellow, and red. The background is a plain, off-white wall. The image shows a step in a density experiment, focusing on the addition of a substance to alter the density of one of the layers.

A hand gently stirs a purple liquid in a clear plastic cup using a small wooden stick. This cup is one of four arranged on a light blue surface; the others contain blue, yellow, and red liquids respectively, creating a rainbow effect. The background is a plain, off-white wall. The image shows a step in a density experiment, illustrating the careful mixing of one of the coloured layers to ensure a smooth, even distribution of colour.

Did you notice that a new colour appears where two solutions meet? You can take your completed rainbow to observe in sunlight or shine a light through it to create a beautiful rainbow projection on the wall.

A hand gently holds a test tube filled with a layered liquid, creating a vibrant rainbow effect. The layers are clearly defined, showing distinct colours from top to bottom: red, orange, yellow, green, and pink. The test tube is transparent, allowing the colours to be seen clearly. The background is a blurred, out-of-focus image of green and yellow tones, providing a natural and pleasing contrast to the bright colours of the liquid. The image suggests a successful science experiment demonstrating liquid density and colour mixing.

The image shows a blurred, slightly out-of-focus projection of a rainbow onto a textured, off-white surface. The colours, though indistinct due to the blur, appear to be layered vertically, suggesting a projection from a cylindrical object containing layered liquids, similar to a rainbow in a tube experiment. The background is a muted, neutral tone, allowing the projected rainbow to be the focal point. The overall effect is soft and ethereal, hinting at the underlying science experiment.

The Science Behind It:

The purpose of adding salt to the coloured water is to increase the density of the solution. Different amounts of salt result in different densities of the coloured water. Solutions with higher density will sink, while those with lower density will float. When we add the solutions in order from highest to lowest density, they stack in layers, forming a relatively stable state, which is the rainbow we see.

Did you notice that we created 7 colours of the rainbow using only 4 colours? Why is this? This involves colour mixing. Using just red, yellow, and blue, and adjusting their proportions, we can create an endless variety of new colours. Try mixing your favourite colours at home.

A Colourful Density Experiment

Materials Needed:

Step-by-Step Instructions:

The Science Behind It:

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