Enzyme Prac Questions...

[jane1234]

Hi all... just have a few questions about the prac we did today...

It was on enzymes... basically we had 6 test tubes of milk, phenolphlalein and Na2Co3.
We added lipase in different amounts (0.5, 1, 1.2, 1.4 and 1.6mL) to the test tubes and timed until the solutions turned from pink to white (the colour the milk was originally).

1. We have to list the uncontrolled variables in the experiment. I have: slight variations between the test tube sizes and measurements of liquid... what others should I include?

2. The test tubes were slightly different widths and lengths, so what effect would this have on the results?
Or what other uncontrolled variable would have an effect on results?

3. We took a class average. What is the purpose of doing this?

4. We had to stir the lipase before using it. Some groups got the last of the lipase and their reactions took longer. Why is this? Why would the lipase at the end not be as effective??

Also, should the hypothesis include prediction of trends (ie what the graph will look like)? We get marked down if its wrong, so would it be safer not to include it but still enough for a good hypothesis?

Any help would be much appreciated

[panicatthelunchbar]

When we did this prac a few weeks ago, our lipase was much stronger, or more 'concentrated' than the lipase of the other class. that did make a difference.
so, you would expect that the higher the lipase amount, the faster the indicator solution, phenolphthalein was at changing colour. remember, that this indicator is pink in alkaline and colourless in acid* (might want to double check on this though) so as the fatty acids react with the sodium carbonate or Na2CO3, the ph is forced to change (Na2CO3 is basic and fatty acids are acids) to a the more acidic side of the ph range, hence, the indicator changes from pink to colourless. now, fatty acids are only produced when milk fats go into a reaction with the enzyme lipase. hope this helps

[jane1234]

Thanks... if the lipase was NOT stirred, would this mean that some areas of the solution were more concentrated than others??

[panicatthelunchbar]

we were not told to stir the lipase before it was put into the mixture, so im not too sure. we only mixed it after it was in the mixture with all the other things in the test tube. sorry :S but i don't see how it can lose its concentration by just leaving it in the tube. for example, if you see water and oil in a glass, you would see oil on the top.
but unless the lipase is mixed with something to prepare it for the prac then maybe, it makes the lipase float on the top giving the groups who took it first faster reactions and the groups at the end slower reactions ? but not sure if this applies here