[ccenet]

I am new to chemistry.  Taking a Biology course and teacher has us mix a solution of 15mL H2O2, 5 mL H2O and 10 mL catalase.  At 6 time intervals we added the solution above to 10 mL H2SO4 (6 different beakers).  We then titrated KMnO4 to determine baseline.  My hypothesis was that as time progresses the catalase will have less effect on the H2O2 because of feedback inhibition.  I failed during lab to understand the results of the titration.  My results per increasing time interval were as follows: .12 mL, .16 mL, .4 mL, .4 mL, .44 mL, .56 mL.

It seems to me to be backwards from what  expected in the hypothesis.  I.E. I expected to use more KMnO4 in sorter time intervals as the catalse worked on the H2O2.  What am I missing here?

[oldddog]

My understanding is that the enzyme (catalase) catalyses the reduction of hydrogen peroxide to oxygen and water;
                 2H₂O₂ ----> 2H₂O + O₂   slow
 2H₂O₂ + catalase ----> 2H₂O + O₂   fast ,
so as time goes by there will be less hydrogen peroxide to react with the permanganate;
 5H₂O₂ + 2KMnO₄ + 3H₂SO₄ ----> K₂SO₄ + 2MnSO₄ + 8H₂O + 5O₂.
Based on the information you provided, I agree with your hypothesis, the results appear backward. However, I disagree with the methodology used to determine the baseline - which I assume to mean the initial amount of hydrogen peroxide in the mixture. This value should be determined by mixing equivalent volumes of reagents without the catalase.

[sdekivit]

2H₂O₂ + catalase ----> 2H₂O + O₂   fast ,

be aware that a catlyst is denoted over de arrow, not in the reaction itself.