pH on amylase practical

• Place one drop of iodine solution into each well of spotting tile.
• Iodine turns blue-black if starch is present.
• Take three test tubes, In the first put 2 cm^3 of starch solution. In the second put cm^3 of amylase solution. In the third, put 2 cm^3 of pH buffer solution.
• Put the three test tubes in a water bath at 30 degrees. leave them for 10 mins to allow the solutions to reach the correct temperature.
• Combine the three solutions into one test tube and mix with a stirring rod. Return to the water bath and start the stopwatch.
• After 30 seconds of the mixed solution being back in the water bath, use the stirring rod to transfer one drop of solution to a well in the spotting tile which contains iodine.
• The iodine should turn blue-black showing that starch is present.
• Take a sample evert thirty seconds and we continue until the iodine remains orange.
• When the iodine remains orange, this tells us that starch is no longer present (the reaction has completed)
• We now repeat the whole experiment several times using different pH buffers for example pH 6, 7 and 8.
• Problems with the experiment

  We are only taking samples evert thirty seconds.

  This means that we only have an approximate time for the reaction to complete. We could address this by taking samples every ten seconds.
• Problem 2 with the experiment

  We are looking for the time when the iodine does not go blue-black. This is not always obvious.

  The colour change tends to be gradual. Some wells might have a small amount of blue-black mixed with orange, so it can be difficult to se then the reaction has finished.