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Hi everyone,

I have an assesable prac for biology students in the coming week,

I need to make solution of pH 3,5,7,9,11. pH 7 doesn't bother me as its distilled water.
But when i am trying to make the other pH its getting in to higher or lower pH .
Do some one have any idea to get it in to the exact pH. I want to finish it by next week .Please help me


Kind Regards
Rakhi

Is it the liver prac with hydrogen peroxide? or something different?

Do you have a copy of 'The Laboratory' by B Dungey? There is a section on making pH buffer solutions, perhaps that will help.

so here is my recipie for making 100ml of stock solutions for the pH prac with Hydrogen Peroxide

pH1: 60ml of 6% h2h02 and 40 ml of bench strength HCL

pH 3: to 60 ml of h2O2 add 38 ml of distilled water, test pH it should be about 5 add drops of HCl until the pH is 3 then top with distilled water to 100ml

pH 6, 7, 8 & 10: 10ml of bench strength sodium hydroxide (2M) make up to 100ml with distilled water reserve this solution.
Take 60 ml of h2O2 and add 30 ml of distilled water, add the reserved NaOH solution until the required pH's are reached then top up with distilled water to 100ml.

pH 12: to 60ml of H2O2 add 35ml of the reserved NaHO solution and measure pH. It should be about 12 but if not add drops of NaHO before topping up with distilled water to 100ml

pH: 13: to 60 ml of H2O2 add 40 ml of bench strength NaOH.


Hope this helps. Sometimes egg whites are used instead of liver if that's what your doing.

Hi jennag,

so we are using 6% hydrogen peroxide in all the steps Right??

Thanks Ev. We do have that book. I will check. Thanks all for supporting a beginner in this field

yes, Is this the prac you are doing? the enzyme one?

it would work with just distilled water and your acid ( the hydrochloric) and your base (sodium hydroxide) to put the pH up or down without the hydrogen peroxide though a fair bit of fiddling

Its working now. Does the PH will be stable for the coming 2 weeks, as i don't get time to prepare the solutions next week.

Thanks everyone for your valuable suggestions


Cheers
Rakhi

the hydrogen peroxide will start to break down esp in light, put in your chem store in the dark. You may also get a bit of gas produced and this can cause the tops to 'pop' off your flasks if they are tight. Just leave a little gap with your stopper and dont put them on to tight.

Thanks Jennag for your valuable advice

Cheers
Rakhi

For this prac we just use
HCl 0.05 M which has a molarity about 2.4
HCl 0.01 M which came in about 4.34
Distilled water 6.5
NaOH 0.01M 9.03
NaOH 0.05 M 11.9
The idea is to show that different pH will affect the action of an enzyme. It didn't really matter if the pH was not exactly 3,5,7,9,and 11.
They were made by diluting my 1M bench reagents and are now kept in dropper bottles in a crate ready for this prac each year.
This is how it is used