Class exercise 4b – Making a density ladder

Aim: To make a density ladder, which can be used to estimate the density of some objects

Apparatus:

  • Boiling tubes
  • One cup each of: glycerine, honey, oil, coloured water
  • Droppers for each cup
  • Rubber gloves
  • Lego block
IMG_2051

From left to right: Oil, honey, glycerine and blue food colouring (to colour the water)

Procedure:

1. A density ladder can be formed by carefully adding the four liquids into a test-tube. Predict the sequence that the four liquid layers will form, starting from the bottom layer.

A: Honey, glycerine, coloured water, oil.

2. Add the liquid into the test-tube, according to the sequence you have predicted. Do not shake the test tube. Can you see four distinct layers? If not, test on another sequence, until you can see four distinctive layers of liquid forming in the test-tube. Write down the sequence (starting from the bottom layer).

A: Honey, glycerine, coloured water, oil. Our prediction is correct!

IMG_2055

Another version of the density ladder that we could take home

Another version of the density ladder that we could take home

We shook the test tube anyway... It came out like this. (It was a separate one.)

We shook the test tube anyway… It came out like this. (This is a separate one.)

3. Given that the densities of the four liquids are: 0.9 g/cm3; 1.0 g/cm3; 1.3 g/cm3; 1.4 g/cm3, match the density with the liquid. Explain your choices.

Liquid Density
Oil 0.9 g/cm3
Coloured water 1.0 g/cm3
Glycerine 1.3 g/cm3
Honey 1.4 g/cm3

A: Less dense liquids will float on top of denser liquids, therefore the densest liquid would be at the bottom, while the least dense liquid would be at the top.

4. Try dropping in the lego block. What do you observe?

A: It floats between the layer of coloured water and the layer of oil.

5. Try dropping the lego block into each liquid. What do you observe?

A: It floats in honey, glycerine and coloured water, but not in oil.

6. Estimate the density of the lego block. Give reasons for your estimation.

A: Its density is 0.95 g/cm3. As it floats in coloured water but not in oil, its density should be between 0.9 g/cm3 and 1.0 g/cm3.

Lego block suspended in honey

Lego block suspended in honey

Lego block sinking in oil

Lego block sinking in oil

Lego block floating in test tube of glycerine

Lego block floating in test tube of glycerine

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