Dodgy practical? (1 Viewer)

[me12345]

Hey,
I had a prac test, testing effect of pH on the enzyme catalase...method was add something like 4 dropperfuls of HCl, NaOH and deionised water to different liver sames, observe pH, then add 3 dropperfuls of hydrogen perioxide...

i got pH w HCl = 4, water = 7, NaOH = 9, and that the water (7) worked best...problem being, everyone else got the NaOH worked best! but i looked it up and it says the optimum pH of catalase is 7!!! is everyone else going to loose marks or am i because im the random?? also what do i say if the teacher claims its not 7? (we havnt got it back yet) Has anyone else done this prac? what did u get???

 

[rooeys2]

lol dont worry, you are right enzymes work the best at ph 7.
are you EVERYONE else got NaOH, or MOST? im pretty sure any fluctuations in pH above 7.5 will DECREASE the enzyme activity
again, dont stress im pretty sure you got it right, maybe the others experienced minor errors

 

[me12345]

I think all of their enzmyes must have denatured in the naoh - thats the only explanation i can think of - oh well hopefully i got it right coz it would really push my ranking up!

 

[Undermyskin]

Wow I don't know that catalase works best at 7. Crap. The problem is if not based on the knowledge from a text book, what can you conclude about the activity of catalase under your experiment condition?

Recently I did a practical test on the influence of substrate concentration on the activity of enzyme. Somehow I got the results totally different from that theoretically. I got the graph of a concave downward parabola instead of a flattening out curve as you must know. I still concluded based on what I knew but not what I got and well, I lost marks, ranked 2nd. From what you've been telling, there are nothing much to say how you can conclude the optimal pH is 7 or 9 at all. Have you forgotten to include more details.

Remember in a practical tests, it's your skills that are being tested, not your knowledge. How can a scientist conclude something correct from what he gets which is conspicuously wrong? There wouldn't be any reliability, validity or accuracy at all.

Good luck anyway.

 

[me12345]

My results were that the most bubbles produced were with a pH of 7 (compared to 4 and 9), implying the optimum pH of catalase is 7.....and thats the thing, according to the net, my results were right....its just that a lot of people seemed to get different results and i dont understand why?

 

[boris]

My results were that the most bubbles produced were with a pH of 7 (compared to 4 and 9), implying the optimum pH of catalase is 7.....and thats the thing, according to the net, my results were right....its just that a lot of people seemed to get different results and i dont understand why?

It's not uncommon for people to screw up, and if a heap of them do it then it can make you feel insecure about your own results.

It appears as though you're correct. Either the other kids have stuffed up along the way or they've misinterpreted the point of the exercise...

Either way, don't stress.

 

[Undermyskin]

So there's nothing to worry. You certainly get full marks for that. However, they can get full marks as well since if they messed up the water test tube thingo, somehow they got most bubbles with NaOH. There's nothing wrong with that though. As said, it's a pratical, not theoretical exam. Remember to record every step you do to justify your validity.

 

[Marinatos]

We did the same prac, but with more substances. The optimum was apparantly meant to be sodium carbonate (approx pH 7.5) but water worked better for everyone in the class. As long as you compare your results to the literature value and talk of any errors, it doesn't really matter if your results were different. In the exams they won't ask you to recount your exact results, only the method and what the expected results would be.

 

[xiao1985]

To OP:

If you still need an answer: water (including distilled) has a pH of s th like 4-5 due to the dissolved CO2. Adding NaOH in this circumstance brings it closer to 7 ( I would imagine)