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Hi all,
I have been asked for peroxide solutions with specific pH's. PH of 3, 7 and 10 I'm not sure how I am suppose to make these up of if the prac book the teacher is working from is confusing pH with concentration? It is for the liver enzyme prac for yr 12 Bio. Help!

Rowyrow,
If you are doing the liver prac I'm sure it should be % concentrations if using peroxide. If unsure get a photocopy of the prac and check it yourself. You should have copies of any pracs the teacher gives you as well as teachers notes for your own reference. Better still the entire booklet or textbook that outlines every prac that the students may do during the year. That way you have a broader understanding of what is going on in any practical and what may be required in the form of equipment, materials and chemicals.
Lyn.

Hi Lyn,
I have the prac book sitting in front of me and it asks for H2O2 with pH of 3, m7 and 10 it must be a consitent typo because peroxide with a pH of 7 is going to be water isn't it and peroxide with a pH of 10 isn't going to be peroxide at all?

The copy of the prac I have here is in two parts.

1. Measures enzyme activity in liver with peroxide where the liver is either cubed, chopped or boiled.

2. Looks at enzyme activity of cubed liver with peroxide at different pH's by adding an equal volume of solutions of
pH3 (1M HCl), pH7 (deionised water) or pH11 (1M NaOH) to three different tubes.

Unfortunately I don't have a book reference but I hope this might help.

Cheers,
Lorna

We have just done this prac with two classes running together. Starting with 6% peroxide (from chemist) reading pH3.
Solutions were made up for 3, 4, 5, 6, 7, 8, 9 pH, by adjusting dropwise with 0.1M sodium hydroxide.
The results are put onto a graph and then they see the trend.

Seemed to work OK.

Rita

I think this is what we do - You have the set concentration of peroxide (we use 6%, 20Vol) and add it to solutions of pH whatever. The peroxide concentration doesn't change. So, you need HCl and NaOH to make the solutions of required pH. I think this is right, anyway. Mush the liver (all the same amount) with the required pH, add the H2O2 and watch the different levels of reaction.

Thanks everyone. It's not needed till thursday next week so I will have a play and see what works best!

Isn't this the one that you can use potato instead of liver?
Sure smells better.
Julie

yeah am going with potatoe, easyer to cube , no smell just better !

If you use potato I slice spud about 1cm thick then use a hand cork borer to cut little cylinders all equal size
Then the kids select and crush and put into test tube with 1 ml distilled water
Put test tubes in differant beakers,
1 Ice water
2 20 C
3 40 C
4 90 C
When stabilised add 1ml 6% Peroxide

Repeat prac at room temp
1 add 1ml sub-strate of 0.1M HCl
2 add 1ml Sub-strate of Distil Water
3 add 1ml sub-strate of 0.1ml Na OH

Repeat prac at room temp
1 no sub-strate and add 1ml 12% H2O2
2 no sub-strate and add 1ml 6% H2O2
3 no sub-strate and add 1ml 3% H2O2

With each reaction they should measure hight of froth and describe size of bubbles
I use graduated test tubes for this prac and they can take direct readings off test tube
So they have a correlation of enzyme reaction at
Differend temps
Different pH
Different strength

great

anyone have the prac in a pdf etc?

RS

I will lay hands on and Fax When do You want it?

Ocker, if you do have a pdf of the experiment would you be able to fax me a copy too.
Thanks Vicki
Fax 02 63863048

OK

If you do a search you will find lots of discussion and probably the prac instructions here on Chemtalk. Try Potato or enzyme?
J

We now do the capsicum version instead of liver thanks to the wonderful Sassi!
The prac method's attached.
To make the extract, roughly chop green capsicum & wizz in a blender till it's a thick soup.
Pour into a funnel lined with chux cloth, & when it's run through, twist up the chux & squeeze as much juice out the last bit of juice.

I usually test it by pouring 6mL of 6% H2O2 into a 50mL measuring cylinder & adding 3mL of the capsicum extract with a syringe.

Time it to 30 secs with a stop watch, & if the reaction's too vigorous & the foam rises past the 50ml mark, the extract is too strong, so I dilute it a little & test again.
What you're aming for is for the full strength extract & the 6% H2O2 to produce foam that rises 45-50ml in the 30 secs.