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Oil and trouble

How do they do that?


You will need:
  • Some cabbage juice indicator or food colours if out of cabbage juice
  • 3 sheets of kitchen roll
  • 2 x paper clips
  • scissors
  • 3 x 100ml beakers, yoghurt pots or similar
  • Vegetable oil - about 100 ml
  • 2 x jam jars or similar ( must be transparent) with lids
  • Washing up liquid
  • Dropping pipette or syringe
  • 2 x test tubes or tall thin 100ml beakers/bottles/shot glasses, (taller rather than wider) and transparent - small bottles will do
  • some kind of measuring cup /beaker (up to 100ml)
  • 200ml boiled ( or distilled) water **
  • Bicarbonate of soda (aka sodium bicarbonate)
  • 50ml Vinegar ( white is best)
  • If no vinegar the juice of a lemon will do


 After 20 minutes ....

 This is what we did!

We prepared 3 beakers: 

  1. Beaker 1 had vinegar, water and red cabbage juice in it .
  2. Beaker 2 had nothing in it
  3. Beaker 3 had water and sodium hydrogen carbonate solution with red cabbage juice.
We then folded up two pieces of kitchen roll into tubes and trimmed them to fit the beaker.

 This is what we found out

When we left the three beakers for 20 minutes or so,  the level of red solution in beaker 1 went down . The same happened in beaker 3. The level of liquid in beaker 3 went up. The liquid in beaker 2 became purple /blue in colour. At the end all three beaker had the same level of liquid in. 

 The tekkie bit..

The paper towels are extremely absorbent. This is because they contain cellulose molecules and air gaps. water molecules are attracted to cellulose and so are drawn up into the material and over into the empty beaker.

The liquid in tube 1 was acidic, that in tube 3 was alkaline. This is shown by the colour of the cabbage juice indicator in each beaker. When the solution beaker 1 mixed with the solution in beaker 3 they neutralised each other and so the cabbage juice indicator changed colour to the blue/purple neutral colour.

This shows how acid can neutralise alkali and how liquid can be transferred from one place to another without pouring, using tubes or pumps.

 This is what we did!

In  tube 1 ( on the left in the video) we placed some diluted vinegar and cabbage juice indicator. We added cooking oil on top. Then we added a small spoonful of sodium hydrogen carbonate powder.

In tube 2 ( on the right) we added sodium hydrogen carbonate solid to some water with cabbage juice in . We added oil on top of this and then added a small about ( 1cm depth) of diluted vinegar to it. Click play to see what happened.

 This is what we found out

In both tubes the two layers stayed separate . In both tubes bubbles rose up through the layers and produced a lava lamp effect . In tube 1 the red colour became more purple in colour. In tube 2 the blue colour became purple.

 The tekkie bit..

Oil and water do not mix; they are said to be immiscible. This is because water is a polar liquid and oil is non-polar ( sometimes called hydrophobic). The oil is less dense than the water and so it floats on top. 

When we added sodium hydrogen carbonate to the acid in tube 1 it sank to the bottom and reacted in a neutralisation reaction .One of the products of that reaction is a gas called carbon dioxide. This bubbles up through the the two liquids. The colour change from red to a more purple colour happened because the acid is neutralised by the sodium hydrogen carbonate.

In tube 2 the effect is the same except the acid was added to the sodium hydrogen carbonate so the colour change was from blue to a more red colour.


Comments 2

David Fowkes on Wednesday, 22 April 2020 17:50

See you at 1500 tomorrow. Any problems with equipment let me know and I'm sure we can improvise. BTW. Purple sprouting broccoli also makes a good acid alkali indicator.

See you at 1500 tomorrow. Any problems with equipment let me know and I'm sure we can improvise. BTW. Purple sprouting broccoli also makes a good acid alkali indicator.
David Fowkes on Thursday, 23 April 2020 15:42

Well done you guys. Good effort . Nice lava lamps!

Well done you guys. Good effort . Nice lava lamps!
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Tuesday, 02 March 2021

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