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Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: jqo2 on January 18, 2015, 02:51:38 PM

Title: Standard Solutions
Post by: jqo2 on January 18, 2015, 02:51:38 PM
I want to prepare a standard solutions (4 times)

I have:


four standards:
                 
             Paracetamol (µg/ml)                    caffeine (µg/ml)

1 -                50                                           20
2-                 75                                           30
3-                100                                           40
4-                125                                           50


In (four) 100 ml flask, can anyone help?
Title: Re: Standard Solutions
Post by: Borek on January 18, 2015, 05:18:50 PM
You have to show your attempts at solving the question to receive help. This is a forum policy.

This is a simple dilution. Have you checked if it can be done in one step? What is the lowest volume you can measure accurately?
Title: Re: Standard Solutions
Post by: jqo2 on January 19, 2015, 02:27:50 PM
I have a pipet p200 (20 µl).

Oke just paracetamol:

1ml Paracetamol stock (2500mg/L) in 99ml H2O gives us solution 25 mg/1000ml.

And then 0,002 from this solution in 9,998 ml H2O --> 50 µg / 1000 ml but a need 50 µg/ml




Title: Re: Standard Solutions
Post by: Borek on January 19, 2015, 02:52:00 PM
If you have no other pipettes or volumetric flasks, you may be not able to prepare the concentration you need.

But in general you are on the right track. It would be probably easier if you were to use μg/mL all the time. For example, what is

Quote from: jqo2 on January 19, 2015, 02:27:50 PM
25 mg/1000ml

in μg/mL?
Title: Re: Standard Solutions
Post by: jqo2 on January 19, 2015, 02:57:30 PM
25 μg/mL

Yes i have other pipettes and volumetric flasks.
Title: Re: Standard Solutions
Post by: Borek on January 19, 2015, 05:21:28 PM
Quote from: jqo2 on January 19, 2015, 02:57:30 PM
25 μg/mL

So you have already overshot your first target.