# did i do it right? - maths and such (Aug/23/2007 )

Yes yes yes anothe rquestion about molarity, i'm sure there are hundreds floating about, i think i did this calculation right ( i am still getting used to this work) but can someone be kind enough to look through it for me???

I have a solution that is 0.50g/l its M.W is 252.32 so its molarity in 1 L is 198.16 m/l correct?

Now i want ot make up a 750 micromolar solution, so if i was to have completed this ......378.482 microliter brough tup to volume of 1000ml would this be correct? i think i am getting worse at this not better!! i want a series dillution ( in 4) so i put 250 ml of high conc into 750 ml water.....and continued to do this for 10 times to make a series dillution. Is this correct?

Going through the calculation I think you're slightly out. Try going through the initial part of the problem. You're almost there just not quite and your calculations are right for the rest of the problem.

Best wishes,

Ceri

Hm, just my 50 cents:

MW 252.32 means 252.32g/L are a 1M solution, or 0.25232g/L would be 1mM, yes?

so 0.5g/L is roughly twice of 1mM (1.98 mM).

1.98 mM is 1980µM - you want a 750µM solution, so you have to dillute your 1980µM 1:2.64 (1980/750, i.e.).

Meaning: use 378µl of 1.98mM, dillute ad 1ml (add 662µl), there you are, 750µM!

For serial dillution with a factor four: you are correct, 250 + 750 is 1:4....... so you take 250µl stock solution, add 750µl dilluent, mix, remove 250µl in a new cup, add again 750µl, and so on....so you will end up with the following dillutions: stock, 1:4, 1:16, 1:64, 1:256, 1:1024..........

Mike

thanks guys...getting there bit by bit