How much n-hexane is needed to extract W to 1.00×10⁻⁴ M?

[tipton12]

Alright, this one is from my analytical chem. class and right now we're doing separations and all the calculations related (partition coefficients, etc.). Anyway, I'm having trouble with this one. It seems easy, but let me know what you think a good starting point would be...

What total volume of n-hexane is required to decrease the concentration of 'W' to 1.00 x 10^-4 if 25.oo mL of 0.0500 M 'W' are extracted with:
a) 25.0 mL portions of hexane

My professor listed the partition coefficient (K) as being 9.6 in problem #1, but it is not stated as to whether that 'K' also applies to this problem too. So I'm confused as to whether I need to start by calculating a new 'K'. This is what was given in problem #1 (which I already finished):

K= [W]hexane / [W]water = 9.6

Please help!
-Jen

 

[Borek]

For a given pair of solvents (water and n-hexane in your case) and for a given substance partition coefficient is always the same (it may depend on pressure and temperature, but these are usually neglected in calculations). So - use the K given.