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luvforums

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Help with calculations...
« on: April 09, 2006, 08:22:42 AM »
I am trying to figure out how to prepare 500 ml of Tyrodes solution (this is a physiological buffer, dont worry, need to know how to carry out the calculations, not to synthesise it) containing 10^-8 M atropine. Tyrodes as well as atropine are STOCK solutions, they're given, and atropine is 10^-3 M. So want to know how to prepare what I said in the first line, using ONLY 2 dilution steps, 100ml and 500ml volumetric flasks and a Gilson that measures aliquots up to 1ml.

I am very confused in my calculations and cannot do this in 2 steps. Anyone could help. ???...thank you
« Last Edit: April 11, 2006, 07:49:47 AM by luvforums »

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Re: Please help with calculations...
« Reply #1 on: April 09, 2006, 03:28:12 PM »
Gilson that measures aliquots up to 1ml.

Up to, is there lower limit given?

And you didn't say what is Tyrodes concentration.
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luvforums

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Re: Please help with calculations...
« Reply #2 on: April 09, 2006, 03:55:44 PM »
Gilson that measures aliquots up to 1ml.

Up to, is there lower limit given?

And you didn't say what is Tyrodes concentration.

Tyrodes concentration is note given, what is important here is the concentration of atropine, Tyrodes is used to add up the volume so to change the concentration of atropine to the desired level.  There is not given a lower limit for the Gilson, the idea is just that we have 3 measuring apparatus, 100ml,, 500ml, and 1ml.

What I think is to take 1ml of atropine 10^-3 and put it in the 100 volumetric flask and add up Tyrodes until full so that now we have a concentration of 10^-5.  Then I have done some calculations but they are mixed up. The idea is that after this step should be another one to end up with 500ml Tyrodes solution (obviously in the 500ml flask) that contains 10^-8 atropine.

any ideas please...

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Re: Please help with calculations...
« Reply #3 on: April 09, 2006, 04:46:12 PM »
Looks like you will need to measure 0.5mL to solve the problem.

Check what will be the atropine concentration if you will dilute twice 500 times, and what will be concentration if you will dilute 500 times and 100 times.
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luvforums

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Re: Please help with calculations...
« Reply #4 on: April 09, 2006, 05:07:07 PM »
Looks like you will need to measure 0.5mL to solve the problem.

Check what will be the atropine concentration if you will dilute twice 500 times, and what will be concentration if you will dilute 500 times and 100 times.

if I take 1ml atropine 10^-3 M and dilute in 100ml Tyrodes, the concentration of atropine wil be 10^-5. If I dilute 1ml from this into 500ml Tyrodes, the final concentration will be 2*10^-8 instead of 10^-8.

2 times 500ml does not give me the answer. What shall I do ???

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Re: Please help with calculations...
« Reply #5 on: April 09, 2006, 05:15:40 PM »
What will be the concentration after two 500mL dilutions?
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luvforums

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Re: Please help with calculations...
« Reply #6 on: April 09, 2006, 06:34:12 PM »
What will be the concentration after two 500mL dilutions?

cannot understand this problem, dont know what to do ???

After 2 dilutions according to my calculations will be 2* 10^-6 the first time and then 4*10^-9.

Please can you tell me something more specific as I have tried all this but none gives me at the end a solution of 500ml Tyrodes with 10^-8M atropine :'(
« Last Edit: April 09, 2006, 06:35:48 PM by luvforums »

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Re: Please help with calculations...
« Reply #7 on: April 10, 2006, 01:52:13 AM »
and then 4*10^-9.

Which is 2.5 times too low. What you can do to make it 2.5 times higher?
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luvforums

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Re: Please help with calculations...
« Reply #8 on: April 10, 2006, 02:15:58 AM »
and then 4*10^-9.

Which is 2.5 times too low. What you can do to make it 2.5 times higher?

Don't know...I have already made two dilutions and this should be done in two single steps.
I have to change sth from the beginning to make it work, maybe...

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Re: Please help with calculations...
« Reply #9 on: April 10, 2006, 02:26:02 AM »

Which is 2.5 times too low. What you can do to make it 2.5 times higher?

Don't know...I have already made two dilutions and this should be done in two single steps.
I have to change sth from the beginning to make it work, maybe...

What if you will take 2.5 mL instead of 1 in the second step?
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luvforums

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Re: Please help with calculations...
« Reply #10 on: April 10, 2006, 05:14:25 AM »

Which is 2.5 times too low. What you can do to make it 2.5 times higher?

Don't know...I have already made two dilutions and this should be done in two single steps.
I have to change sth from the beginning to make it work, maybe...

What if you will take 2.5 mL instead of 1 in the second step?

It looks great because as a result we will have what is required and prepared in 2 steps!   :D

But I don't think this is the right way because I am provided with another 100ml volumetric flask which I haven't used at all and this makes me doubt. Also don't think that using 1ml gilson for taking 2.5 is right. Obviously if there is no other way of solving this, I'll have to accept this one, but there should be sth differentr in my opinion.
What do you think?
« Last Edit: April 10, 2006, 09:12:40 AM by luvforums »

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Re: Please help with calculations...
« Reply #11 on: April 10, 2006, 01:17:25 PM »
But I don't think this is the right way because I am provided with another 100ml volumetric flask which I haven't used at all and this makes me doubt. Also don't think that using 1ml gilson for taking 2.5 is right. Obviously if there is no other way of solving this, I'll have to accept this one, but there should be sth differentr in my opinion.

AFAIK there is no other way to solve this problem. Let me know if you will find something better.
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luvforums

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Re: Please help with calculations...
« Reply #12 on: April 10, 2006, 06:50:31 PM »

AFAIK there is no other way to solve this problem. Let me know if you will find something better.

I found out a solution that seems to be "more correct" to me.
In the first step I take 1ml of atropine 10^-3 M and dilute in a volume of 100ml. Now the concentration is 10^-5 M. Then take 0.5 ml from it and dilute in the 500ml flask, so the final concentration will be 10^-8 M.

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Re: (UPDATED, please read) Help with calculations...
« Reply #13 on: April 11, 2006, 02:44:03 AM »
It still requires you to measure 0.5mL.
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luvforums

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Re: (UPDATED, please read) Help with calculations...
« Reply #14 on: April 11, 2006, 04:51:51 AM »
It still requires you to measure 0.5mL.

Yes, I know, it couldn't be done with 1ml measures only, but at least I managed to include the 100ml volumetric flask and measuring 0.5 ml is relatively easier than 2.5 and the use of 500ml twice makes it less 'confortable' because we have got only one flask.
Thank you for the help

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