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# Help! % solution confusion

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### #1 phosphate girl

phosphate girl

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Posted 12 May 2010 - 12:57 AM

Hello,

This may seem like an obvious question, to those of you mathmatically inclined, but I am used to making up solutions using Moles. I was give a 32 % solution of stock HCl and told to make up 2 Lts of a 1 % working stock of HCl. I have sat for about 15 minutes now trying to work it out but just can't seem to do it. I know it's probably obvious and the 3 hrs sleep I had last night are not helping. Can anyone please explain to me how I should work this out, your help would be much appreciated!

Thanks

### #2 Prep!

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Posted 12 May 2010 - 01:03 AM

phosphate girl, on May 12 2010, 03:27 PM, said:

Hello,

This may seem like an obvious question, to those of you mathmatically inclined, but I am used to making up solutions using Moles. I was give a 32 % solution of stock HCl and told to make up 2 Lts of a 1 % working stock of HCl. I have sat for about 15 minutes now trying to work it out but just can't seem to do it. I know it's probably obvious and the 3 hrs sleep I had last night are not helping. Can anyone please explain to me how I should work this out, your help would be much appreciated!

Thanks

N1 (Stock pconc - percent in your case) V1 (to find out) = N2 (required conc) V2 (required volume)

Therefore
32*? = 1 * 2000 ml

? = 2000/32
= 62.5 ml

So you need to take 62.5 ml from the stock and make up the volume to 2 liters.
Hope this helps

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### #3 Prep!

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Posted 12 May 2010 - 01:05 AM

it can also be solved as

Required percent is 1 and stock percent is 32 which means you need to dilute it 32 times to get a 1% solution from 32% stock
you require 2 liters which is 2000 ml
So 2000/32 (REquired volume/dilution factor)
= 62.5ml

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### #4 phosphate girl

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Posted 12 May 2010 - 01:10 AM

That's great! Thank you very much - so simple as well *groan* I should be banned from the lab. until I get a good nights sleep.

Thanks again

### #5 Prep!

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Posted 12 May 2010 - 01:21 AM

phosphate girl, on May 12 2010, 02:40 PM, said:

That's great! Thank you very much - so simple as well *groan* I should be banned from the lab. until I get a good nights sleep.

Thanks again

haha.. u  need not curse yourself.. this happens to only great minds!!!
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