Oserving the properties of water. Place a drop of water on a smooth plastic sheet or on the bench. Look at it closely from the side.

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CR yr12        Biology        01/11/2010


Experiment # 1: Place a drop of water on a smooth plastic sheet or on the bench. Look at it closely from the side. Draw the outline of the drop. How are the molecules held in their place?

  • The drop of water and the drop of detergent have a different thickness, because the molecules are held differently. The drop of water, in fact, has a higher thickness. The molecules are closed to each other and it's possible to notice the surface that behaves as an elastic membrane that surrounds and compresses the underlying liquid. There is a force of cohesion that determines the surface tension.                                                                                                                                                                     
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Experiment #2: Fill a clean 250 ml. beaker with water to about 1 cm. below the top. Carefully float  a small filter paper on the surface. Carefully drop a needle, exactly horizontal, on the paper. Wait until the paper becomes soaked and sinks. Observe the needle carefully. After you have observed it, add one drop of detergent with a glass or plastic rod.

  • the piece of paper floats on the water and then it sinks because it get too wet. the needle continues to float, although its specific gravity is higher than the water's one, maybe because the water ...

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Minor grammatical errors present in places, also some careless spelling mistakes present. Other than this most of the document is fine in terms of punctuation, grammar, spelling and layout

The experiments are very cleverly done and an attempt is made at an explanation. However, the first explanation of cohesion is not very well done. Bonds between water are explained at a base level. The diagrams help in the explanation and the methods of each experiment are stated clearly. One or two hypothesis seem to be guesses but most of the candidates work is correct even though it lacks deeper scientific detail.

Overall a cleverly carried out and explained experiment. It provokes thought from the reader and the candidate shows well thought out reasons as to why each experiment proceeds as it does. To improve their mark, the candidate should include a conclusion on the properties of water tying all the different experiments together.