[arronsparrow]

Would anyone happen to know the reason to as why when I am titrating a solution of 10mL 1.0M Sulfuric Acid, 10mL 1.5% Hydrogen Peroxide, and 1mL of Water using (0.1M?) Potassium Permanganate, that the titration fails instantly, as in turns pink within 1-2 drops? This was previously for a lab that my AP Bio class had done on enzymes in which we needed to establish a baseline as a control before adding in catalase, hence the water in lieu of the catalase. This is different from results that I have read about failed titration as most of them detail adding a lot of titrant and not getting a result, whereas mine is the complete opposite. Any clarification about this would be helpful as I do not know why the titration has occurred this way. Cheers -Alexander

[Arkcon]

Can you calculate, for us, right now, what was expected?  What would you expect, if there was no peroxide, as in plain water, or with catalase added?  What would you expect for exactly half degraded peroxide?  Can you write those examples for us out, outside of a breathless box o' text?

This is the best way to get to the bottom of what, if anything, is wrong.

FWIW, I've done this very titration, in an industrial setting, for commercial peroxide wipes.  I squeezed the juice out, acidulated, and titrated with standardized permanganate.  After a year in storage, there was not as much left, as the label claimed, by my calculations.  But there was still some there, in comparison to the blank.

[arronsparrow]

Sorry for the bland text, I was typing this on my phone at about 1am. Anyways, back to the original problem.

The experiment was to be done in two parts, establishing a baseline, and over a course of 0 seconds to 360 seconds. We expected the baseline beaker to take around 8-10mL of KMnO₄. In the timed trials, subsequent intervals at 0, 10, 30, 60, 90, 120, 180, and 360 would take less KMnO₄ to neutralize. In these timed trials, the sequence of solutions being added would have been, H₂O₂, catalase, and after the allotted time, H₂SO₄, and finally KMnO₄ to titrate.

What I would expect from no peroxide in the solution and being only plain water with the addition of KMnO₄ would be that the addition of KMnO₄ would give us a nice purple solution. The addition of H₂SO₄ to the plain water I believe, would give us no visible color change in the KMnO₄.

The catalase, comes in the second part of the experiment however, through the timed trials since the 21mL solution replicates what happens after the reaction between Hydrogen Peroxide and catalase is stopped by Sulfuric Acid. With the catalase, since it is reacting with the peroxide, I would expect the amount of KMnO₄ needed to turn the solution to be less as time went on.

What I would expect for half degraded peroxide, since the solution would have degraded into H₂O and O₂, if it were used in the original 21mL solution of Sulfuric Acid, Water, and Hydrogen Peroxide, would still have been a reaction between the KMnO₄ and Hydrogen Peroxide. Since the Manganese in KMnO₄ is bound to Oxygen and once it reacts it loses that Oxygen and turns into Manganese ions Mn²⁺. The amount of KMnO₄ needed would have been 5mL of the 10mL that we used in the baseline.

One thing to note is that using the same materials that day, my group was the only one to get the baseline and 10 second beaker to titrate properly once, resulting in us using 9-10mL of KMnO₄ to neutralize the solution. However, subsequent attempts to recreate this process failed, even with the timed trials.

My memory is a little fuzzy on recalling the data since we did this lab a month ago, and my my lab journal is being graded by my teacher, so I do not have some of the more fine details that were observed.

[Arkcon]

If you're still interested in this topic when you get your journal back, please give us the results in the form of a table: what was there, and what it took to produce a color change.  This will help us understand.  Your occasional number in a wall of text isn't helping.

Some points:

What I would expect from no peroxide in the solution and being only plain water with the addition of KMnO4 would be that the addition of KMnO4 would give us a nice purple solution. The addition of H2SO4 to the plain water I believe, would give us no visible color change in the KMnO4.

OK.  This isn't how a simple titration is done.  What's done is, you add reagent dropwise, either stirring mechanically or swirling manually with each addition.  The palest color, that persists with stirring, is the endpoint.  You record that volume on paper, and you accept that volume.  You use that volume, in a calculation, that tells you how much was there.  And that's what I wanted to see.

A bright purple color is very overshot.  You'll find, once you hit an endpoint like I described, if you add 1 ml more, then 5 ml more, then 10 ml more, no discernible difference in the color.  So if you see a bright purple color, you know nothing at all -- you don't know if you've added 1ml, or 5ml or 10 mL too much.  But you can't use that number in a calculation.

What I would expect for half degraded peroxide, since the solution would have degraded into H2O and O2, if it were used in the original 21mL solution of Sulfuric Acid, Water, and Hydrogen Peroxide, would still have been a reaction between the KMnO4 and Hydrogen Peroxide. Since the Manganese in KMnO4 is bound to Oxygen and once it reacts it loses that Oxygen and turns into Manganese ions Mn2+. The amount of KMnO4 needed would have been 5mL of the 10mL that we used in the baseline.

There is nothing quantitative in this statement.  And that makes me sad.  I had such high hopes at the beginning of the paragraph, and then you describe the reaction from the textbook, instead of what you saw.  Highly disappointing.

[arronsparrow]

Let me start by making clear some points:

• The Purpose of this lab was to determine how much Hydrogen Peroxide is remaining after a reaction containing no catalase (baseline) and catalase (timed trials).
• I want to know why, when using Potassium Permanganate to find the amount of Hydrogen Peroxide remaining, that after 1-3 drops, the solution turns pink.
• I am a high school student who does not have access to half of these chemicals or supplies, so most of the responses I type are going to be simulated in my mind sadly.
  

What would you expect, if there was no peroxide, as in plain water, or with catalase added?  What would you expect for exactly half degraded peroxide?

This isn't how a simple titration is done.

I was not sure that you meant under these conditions, what I would expect if I titrated them, or if that's what I'm getting from this.

What would you expect for exactly half degraded peroxide?

Again, what exactly are you wanting from me by stating "expect." There are many things I can expect from observing degraded hydrogen peroxide. Noticeably that it looks the same as new hydrogen peroxide and reacts less strongly. It decomposes very slowly into Water and Oxygen gas and in the presence of a catalyst, the reaction becomes more noticeable giving off lots of oxygen gas.

OK.  This isn't how a simple titration is done.  What's done is, you add reagent dropwise, either stirring mechanically or swirling manually with each addition.  The palest color, that persists with stirring, is the endpoint.  You record that volume on paper, and you accept that volume.  You use that volume, in a calculation, that tells you how much was there.  And that's what I wanted to see.

A bright purple color is very overshot.  You'll find, once you hit an endpoint like I described, if you add 1 ml more, then 5 ml more, then 10 ml more, no discernible difference in the color.  So if you see a bright purple color, you know nothing at all.

Yes, I understand how to do a simple titration, the expected endpoint was to be 8-10mL, instead we got .2-1mL for the endpoint. Which clearly indicates something is wrong, but the reason to is unknown, hence why I am asking this on the forums so that I may gain understanding from others with experience or knowledge of this field to be able to help me.

There is nothing quantitative in this statement.  And that makes me sad.  I had such high hopes at the beginning of the paragraph, and then you describe the reaction from the textbook, instead of what you saw.  Highly disappointing.

Quantitative... I do not recall being taught how to gather quantitative or qualitative data in any of my high school classes, so this may be a significant disadvantage to the responses you will get from me. Upon doing a quick reading, I assume two things that you wanted from me: Numbers and Calculations. However, what was needed to be calculated?

Anyway, enough ranting, onto the data.

This is the data my teacher got when he did the lab beforehand:

Time Interval	Amount KMnO4 to neutralize (mL)	H2O2 Consumed
0	6.37	0.0
10	6.03	0.3
30	4.70	1.7
60	6.23	3.7
90	3.61	2.8
120	2.75	3.6
180	1.53	4.8
360	1.25	5.1

And this is essentially what we got when we did the lab:

Time Interval	Amount KMnO4 to neutralize   (mL)	H2O2 Consumed
0	.2	?
10	1	?
30	.6	?
60	.4	?
90	.2	?
120	.2	?
180	.2	?
360	.2	?

Results and data that not even my bio and chemistry teacher and the whole class could figure out.

Notable Points:

• The Hydrogen Peroxide used was new and store bought diluted to a 1.5% from a 2.0% solution using distilled water.
  
• Distilled water was the only water used in the experiment and used to dilute all the compounds.
  
• The Catalase was made using chicken liver, stored on ice for the entire duration of the experiment.
  
• All the chemicals used were aqueous.
  
• All the materials and experiments were created and done on the same day.
  

If you want anything else, please explain to me what you want and if there are specific conditions. The terms used, "what was expected" and "what you would expect..." are quite ambiguous and I assumed from your original statements, that if I had a beaker of plain water (with or without sulfuric acid) and no peroxide, what would happen if I added KMnO₄ to it. Either way, titrating or adding KMnO₄ to that solution wouldn't necessarily change color, I believe; if I am wrong please correct me. Please also keep in mind that I am new to these forums and do not know how responses are wanted here, so clarification would be great.

Sorry for the excessive quoting at the beginning, but it was unclear what was needed from me, however I feel as it is mostly my fault as I did not ask beforehand for clarification.

Edit: If its worth mentioning, my teachers, a couple of seniors and I did a bunch of experiments after class that same day changing different variables in the experiment. Some of which included, changing the molarity of the chemicals, sequence of the chemicals added, and time for the reaction to take place or to be left undisturbed before titrating. All of which ended in the same result, a 5mL sample extracted from the 21mL sample turning pink within 1-3 drops. I also have a link to the lab we did if you need it.

[Borek]

Have you observed bubbling after combining the catalase with the hydrogen peroxide solution?

1-2 drops is what it typically takes to reach the endpoint in a blind test (titration without the hydrogen peroxide present). If that's what you got in all cases my bet is that there were no H₂O₂ in the solution at all. No matter why - error during solution preparation, faulty sample bought, whatever. I would perform experiments to compare the sample used with other samples (hydrogen peroxide from another source, separately prepared solution and so on).

[arronsparrow]

When the catalase was added to the hydrogen peroxide, bubbling was observed to be quite violent at first and a large volume of oxygen gas and water were seen. As time went on the reaction diminished in intensity and after the allotted time was stopped by adding Sulfuric acid, essentially denaturing the enzymes due to a low pH.

It may have been faulty solution preparation, however, we were able to successfully titrate a sample from the reaction once (in class) before it stopped working, while my teacher did the entire experiment before class started by himself and got the results in the data above.

A faulty sample of hydrogen peroxide I would think to be the least likely cause of this scenario as they were unopened store bought bottles of hydrogen peroxide. We opened two other bottles and brought some from other classrooms to experiment with as well