The high surface tension of water can be demonstrated by a simple and effective display.
You will need a glass of water and piece of paper.
Fill the glass with water to the very top as shown below.
Make sure there is no air space between the surface of the water and the top of the glass.
Place the paper over the top of the glass pressing down on the surface of the liquid. Turn it upside down and watch how the water is supported by the paper.
View the video on the right to see how this trick works.
What role does H-bonding play in this trick?
Will it work with other liquids that do not exhibit H-bondng?
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Below are a number of investigations that can be conducted. Groups select one or two investigations, as some are more involved than others.. The results are written up and shared with other groups. This gives students an appreciation of the need to write reports so that others can understand how the investigation was conducted and the results obtained. Students use the collective results to work out how the trick works.
Water has some special properties. It can be very sticky and forms a thick surface layer that can support small objects, as shown on the right.
Water, however, has other special properties. One of which is demonstrated in the video on the right. A balloon is charged with static electricity and brought close to a column of water.
What can you say about the water molecules? Give your reasons.
1) After looking at the video suggest what keeps the water from pouring out. Form a hypothesis
2) Does the trick work as well with other liquids such as oil, or alcohol.? Investigate
3) Does the trick work with plastic, paper or glass cups? investigate
4) A student suggested that a vacuum forms at the bottom of the glass as the water tries to pour out which sucks the water back into the glass. Investigate
5) Is it important not to trap air inside the glass? Investigate
6) Is there a limit to the column or mass of water that can be supported in this way? Investigate .
7) Is there a relationship between the mass of water that can be supported and the size of the opening of the cup? Investigate
8) Is there an optimum temperature of the water at which this trick works best? Investigate
9) With clear evidence from your investigations , suggest how the water is supported in the glass.
