8 – Bicarbonate Indicator, Photosynthesis and Respiration

This is the homework fro 10/01/13. The topic of bicarbonate indicators is difficult, so you will need to research it if you don’t get it at first. The following website has good explanations appropriate to your ability http://www.jgsee.kmutt.ac.th/exell/JEE613/WriteExpt.html.

Bicarbonate indicator

Bicarbonate indicator is a solution that has been carefully prepared so that it is at the precise pH where it is a dark red-orange colour. Carbon dioxide is an acidic gas, which dissolves in water to form something called carbonic acid. If the pH of the indicator becomes slightly more acidic the indicator turns yellow. If it becomes less acidic, the indicator turns purple.

  1. Draw a labelled scientific diagram to show the set-up of the experiment in the space below:
  2. A sample of elodea is placed in a test tube, submerged in bicarbonate indicator solution. The test tube is covered in black paper to prevent any light reaching the plant. Describe how the rate of photosynthesis would compare to the rate of respiration and use this to explain why the bicarbonate solution turns yellow.
  3. A sample of elodea is placed in a test tube, submerged in bicarbonate indicator solution. A bright light is shone onto the test tube. The bicarbonate indicator solution turns purple explain why.
  4. Explain the role of the third test tube, containing bicarbonate indicator, but no elodea.
  5. What has the experiment proven?

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