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Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: payata on April 16, 2019, 08:40:19 AM

Title: Calculate the concentration (v/v%)
Post by: payata on April 16, 2019, 08:40:19 AM
Hey Guys!

I have a problem with task below, hope you can navigate/ help me with it ???

In a 100 mL measuring flask 30 ┬ÁL of butan-1-ol is placed by pipetting, The flask is filled to the mark with technical grade acetone,

The solution is analysed once and the following areas are found:

                
Area of
propan-2-ol   854
Area of
butan-1-ol           405

Calculate the concentration (v/v%) of propan-2-ol in the sample, Show the calculations:

What I did until now, I deviated Area of sample / Area of Internal standard (which is butan-1-ol, 0,03% v/v), I know that concentration I should find by drawing standard curve, but how if concentration is not given?

So formula should looks like that: c= (Area of sample/Area of IS - intercept)/slope . but, how to calculate concetration to draw std curve?  ???

Thank you in advance!




Title: Re: Calculate the concentration (v/v%)
Post by: Borek on April 16, 2019, 09:27:12 AM
The only thing you can do it to assume signal to be directly proportional to the surface area.

This is equivalent to assuming at C=0 Area=0 - this way you have two points to build your curve on.
Title: Re: Calculate the concentration (v/v%)
Post by: payata on April 16, 2019, 10:03:27 AM
I'm not quite sure if assumec=0, please look below

the answer is given c= (854/405+0,0116)/35,529 = 0,0597%

this is what the Lecturer gave to us ??? and I really do not how he got intercept, and slope for that, plus concentration

Title: Re: Calculate the concentration (v/v%)
Post by: Borek on April 16, 2019, 10:10:58 AM
There is no way to derive the formula used from the numbers given, so either you are missing something (earlier part of the lecture, page in a book, whatever), or you were given incomplete data.
Title: Re: Calculate the concentration (v/v%)
Post by: payata on April 16, 2019, 12:07:59 PM
All class got same as I, so I think I will write to Lecturer and confirm :D

Thank you for reply!