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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: Vodkaz on May 19, 2021, 06:45:47 AM

Title: Question about dilutions
Post by: Vodkaz on May 19, 2021, 06:45:47 AM

Hello, I have to prepare a stock solution of 10 mg caffeine and 1 ml acetonitrile, from that stock I need to make some standards with concentrations: 1; 05; 0.1... and so on (mg/ml). It's clear that I have to calculate the concentration of stock but I'm not sure how to; it's important to say that density of caffeine is not given just volume of the vessel (2ml Eppendorf tube). What other calculations should I do in order to obtain the volume of the standards?.

Title: Re: Question about dilutions
Post by: Babcock_Hall on May 19, 2021, 09:30:10 AM

One does not need the density of caffeine in order to perform this calculation.  The standard formula for dilutions (C₁V₁ = C₂V₂) can be used, but in my experience students sometimes plug in wrong values.  My usual suggestion is to draw a picture, to avoid errors of this kind.

Title: Re: Question about dilutions
Post by: jeffmoonchop on May 19, 2021, 01:26:04 PM

The concentration of the stock is 10mg/ml, due to you dissolving 10mg into 1ml.