Question

Prepare
50 ml of
25 ppm
k from
100 ppm k solution​

Answer 1

Answer:

Use the standard dilution formula in general chemistry, i.e., Volume(1) x Concentration(1) = Volume(2) x Concentration(2). Make sure all your units are the same. Thus, you can either change 1000 ppm to ppb (1000 ppm x 1000 ppb/1ppm) = 1000000 ppb or you can change the ppb needed to ppm. So, you have a stock solution of 1000000 ppb (concentration 1), and you want to know what volume(1) to dilute to make a stock solution of whatever volume you want (for example 100 mL). Thus, if you want 5 ppb, the formula is ? mL(1) x 1000000 ppb(1) = 100 mL(2) x 5 ppb(2). Solve for ? and you have the volume you should add to a 100 mL volumetric flask. Bring it up to volume and you're good to go. Note that this formula is universal but from a practical aspect you would only be pipetting 0.0005 mL of your stock to get your 5 ppb. Thus, using a 1000 ppm stock to start is not practical. I suggest that you make a 1 ppm stock and start from there. Take 0.1 mL of your 1000 ppm stock and dilute it to 100 mL (use a volumetric flask for accuracy and convenience). Then, re-run the calculation using the dilution formula. To avoid waste, and depending on the volumes you need, you can proportionally cut the volume of all your stocks.

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