[_cheers]

Hi guys,

I am diluting an ASA sample in NaOH up to 250 ml of water (after hydrolizing the acid). I then take out 5 ml and dilute it up to 50 ml of Fe+ solution (M=0.2).

I figured the first thing was calculate the concentration in 250 ml : .2281 mg ASA/ 250 ml = .009124 mg/ml ASA sol'n. Can I then just take out 5 ml/ 250 ml  and divide that amount by 50 ml of the Fe solution? but if its 'up to 50 ml', then I'm adding only 45 ml...

[english]

First you need to make sure you convert your stock soln.to mol/L, as this is how molarity is defined.

M₁V₁ = M₂V₂

Where M₁ is the molar conc. of your stock soln. (in mol/L), V₁ is the volume (in L) of your stock soln.

M₂ is the molar concentration of your desired dilute soln. (mol/L), and V₂ is the volume of your desired dilute soln. (L)


Simple equation that skips the headaches, and proposes one simple aspect:  the number of moles of solute does not change upon dilution.


Have fun. 

[_cheers]

I'm sorry, I cant see how that works with this. I have a  molar concentration for my stock solution (ASA sample + 250 ml water), but I have to take out 5 ml, (then 4, then 3 then 2, then 1) which then gets diluted 'up to' 50 ml with added [Fe(H20)6]3+

So, isnt the concentration of th stock solution (in 5 ml) to make a standard solution with the Fe....= : mass of sample x 5 ml/250 ml

that solution is put in a vol. flask and filled up to 50 ml, so I am adding 45 ml, then 44, 43, 42, 41 for each standard solution.

So, I have an M for the stock solution, and V, also an M (.2M) and V(45,44,43,42,41 ml) for the Fe solution

This is all to use spectophotometric determination of ASA via absorption methods.

What I dont understand is how the Fe solution fits into the equation.. so, I have Fe and my stock solution in one flask...

does that help? or make it more confuddled ?

[Borek]

k.V. answer contains all necessary information. You must be overthinking the problem. Just remember that V₂ is a final volume - so it is 50 mL in each case (you filled up to 50).

[_cheers]

yes, I overthink a lot of it. I think I got this one. But one more thing..and its super simple but I'm drawing a blank...how do I find out the mass of the ASA tablet with concentration (mg/ml). I have my mass of the tablet, the given mg of it...I'm drawing a complete blank...