Expert: Michael Simone - 2/24/2004

Question
Hello,

 I am trying to get the concentration for a standard solution. (Of Aspirin)

First I added 1mL of a .010 M aspirin sol'n to a beaker. I then added 5mL of a .1M NaOH sol'n to the aspirin. This mixture was added to a 100mL Erlenmeyer flask and 4 mL of "Solution A" was added. The beaker was then filled to its mark with H2O. I calculated .0018g Aspirin in sol'n. by using its MW and .010M concentration with the volume 1mL but need to get to its Molarity. It seems that some volume other than the 1mL is needed in finding the concentration of the. standard sol'n.

-Any help would be greatly appreciated.

Thanks, Josh

Answer
Let me make sure I understand. You have 1ml of aspirin at 0.010M, you then dilute that 1ml in “solution A”, and water to a final volume of 100ml?

If this is correct, all you did was dilute the original aspirin solution 100 times.  Your final concentration is then 0.0001M.  Use the dilution equation V1C1 = V2C2 where V is volume and C is concentration. You know V1, C1 and you final volume V2 is 100mls, so you should be able to solve for V2.

Also you state that you have, based on your original 1ml of solution, 0.0018g of aspirin. So divide your weight by the molecular weight to arrive at the number of moles of aspirin you have:

0.0018g/180.15g/mol = 0.000010mols. Now since you have 0.000010mols, divide by the volume in liters and you have:

0.000010mols/0.10L = 0.0001M.

Does this help or did I miss the question?

Good luck,

Mike