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Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: ziagemini on July 10, 2012, 09:23:03 AM

Title: Original Concentration
Post by: ziagemini on July 10, 2012, 09:23:03 AM

Hello All,

i have a question regarding the concentrations. I have a sample i dilute it mass-maas. 30grams of sample+600grams of DW. Then i find the concentration of acetic acid present. It is 0.04M. Now how much is the concentration of acetic acid in original sample. As i did 1:20 dilution. And i remember we have to multiply this so in original solution acetic acid concentration is= 0.04M*20=> 0.8M.

Am i right? Thanks for the help.

Regards!

Title: Re: Original Concentration
Post by: sjb on July 10, 2012, 10:11:35 AM

Quote from: ziagemini on July 10, 2012, 09:23:03 AM

Hello All,

i have a question regarding the concentrations. I have a sample i dilute it mass-maas. 30grams of sample+600grams of DW. Then i find the concentration of acetic acid present. It is 0.04M. Now how much is the concentration of acetic acid in original sample. As i did 1:20 dilution. And i remember we have to multiply this so in original solution acetic acid concentration is= 0.04M*20=> 0.8M.

Am i right? Thanks for the help.

Regards!

Not quite. What is the total mass of your diluted solution.

Title: Re: Original Concentration
Post by: ziagemini on July 11, 2012, 04:28:24 AM

The total mass:

Original sample= 31.10 grams
DW added=       622.44 grams
Total mass after dilution = 653.54 grams

Hope this helps.

Regards!

Title: Re: Original Concentration
Post by: sjb on July 11, 2012, 06:05:36 AM

Quote from: ziagemini on July 11, 2012, 04:28:24 AM

The total mass:

Original sample= 31.10 grams
DW added=       622.44 grams
Total mass after dilution = 653.54 grams

Hope this helps.

Regards!

So is the total mass 20 times the original mass? How does this affect the concentration?

Title: Re: Original Concentration
Post by: ziagemini on July 11, 2012, 06:34:19 AM

That's what i want to calculate. I don't know the original concentration. That i want to find out. Is there any general rule for that or it differs from acid to acid.

Title: Re: Original Concentration
Post by: Borek on July 11, 2012, 06:40:40 AM

Mass is conserved, so no matter what you dilute amount of substance in the solution after dilution is identical with the mass of the substance that was present in the original sample before dilution.

Title: Re: Original Concentration
Post by: DrCMS on July 11, 2012, 06:43:35 AM

You are not reading the questions you are being asked properly.  

We know what you want to calculate we are trying to help you work out how to do it correctly; so you understand and can apply it to other situations rather than just giving you the answer in this case.

How to do this dilution calculation correctly has nothing to do with the materials involved.

Lets take a different example:

If you have 1 red ball and add it to 20 black balls what is the chance of picking a red ball?