Need help calculating concentration

[Edwin_K]

Hello all,

I'm a physiologist by trade but was recently assigned a chemical job, and my chemist supervisor is not willing to help..would really need help from anyone right now.

- 1st, we mixed 1ml PBS solution into 9ml DD H2O and then 10ml of this solution was further mixed into 990ml DD H2O. (This final solution of PBS-DD H2O is hereby known as solution A)

 

- Say we mixed 1ml of H2O2 (30%) with 99ml of the solution A creating solution B,

- And then 1.5ml of solution B was mixed into 1.5ml of solution A, what is the concentration of H2O2 in the 3ml solution?

Thank you very much in advance!!

And sorry if im confusing and/or using inappropriate terms, im really not a chemist by trade.

Edited March 14, 2014 by Edwin_K

[studiot]

First question, does the PBS react with the hydrogen peroxide?

 

 

If it doesn't then

 

The first part (preparation of solutution A) is irrelevant.

 

In the second part you started with a certain quantity of peroxide in 1ml of liquid and ended up with the same quantity in 100ml so you have divided the concentration by a factor of 100.

 

In the third part you have halved the concentration by the same reasoning.

Edited March 14, 2014 by studiot

[Edwin_K]

Thanks studiot for replying, to clarify things:

 

Since PBS is used for substance dilution, i assume there will be no reaction between PBS and H2O2?

We were instructed to dilute PBS by a factor of 10 with distiled H2O, and then the diluted PBS was then diluted again with DD H2O by factor of 100, so can we call the solution A as PBS diluted by a factor of 1000?

We were then instructed to mixed the PBS (diluted by a factor of 1000) with pure H2O2 (30%) by the ratio of:

1ml H2O2 : 99ml PBS (diluted by a factor of 1000)

which creates solution B (diluted H2O2).
At this point, is it safe to say the concentration of H2O2 is 1%? Or can we calculate the molarity of H2O2 at this point?

 

Next, say 1.5ml of Solution B (diluted H2O2) was then mixed with 1.5ml PBS (diluted by a factor of 1000)..is there a way to calculate concentration of H2O2 in mol or other unit at this point?

[manu9]

You have all the information you need to prepare your solution (assuming 22.05 M is the correct concentration of your H2O2). However, you did not provide us with the volume of this stuff that you need to make. Let's assume you want to make 100 mL of a 1M solution of H2O2. Using the general dilution equation M1V1=M2V2 you will have :

 

(22.05 M)(v) = (100 mL)(1.00M)

 

Solving for "v", you'll get the volume you need to pipet from the big bottle of H2O2, which comes out to be about 4.6 mL.

So, using a pipet, transfer 4.6 mL of H2O2 into a 100 mL volumetric flask. Fill the flask to the "mark" using the phosphate buffer.

 

I hope this helps!

 

E_Sik