[novice]

I am having trouble solving this problem, any help would be much appreciated.

Question: An aqueous soulution of Br2 is shaken with CCl4 (immiscible with H2O) at 25 degrees celcius until equilibrium is attained. The final ratio of the molarity of Br2 in the aqueous solution to the molarity of Br2 in the CCl4 solution is 0.035. Find the volume of CCl4 that must be shaken with 50mL of an aqeuous solution of Br2 in order to extract 95% of the Br2 from the aqueous layer.

Answer: 33.25mL

I have been using the formula Kd=[Br2(aq)]/[Br2(CCl4)]=0.035 without success.

Thankyou!

[Yggdrasil]

I get 33.25mL when I use that formula.  Show your work so that we can help find where you are making a mistake in your calculations.

[novice]

Kd=[0.95x(1/50)][.05x?]=0.035

?=36.84mL

=/

[Yggdrasil]

Let's say you have x moles of Br₂ originally in your aqueous solution.  After extraction, you want 0.05x moles in 50mL of the aqueous solution.  Therefore, [Br2(aq)] = 0.05x/50.  Similarly, you want 0.95x moles of Br₂ in a certain volume of CCl₄.  Let's call that volume V.  Therefore, [Br2(CCl4)] = 0.95x/V.

Now, what set up your equation for Kd and solve for V.  You will find that the x cancels out.

[novice]

Thankyou for your help, although i am still struggling to understand why you put 5% aqueous solution and 95% CCl4, i assumed it would be the other way around.

[Yggdrasil]

Find the volume of CCl4 that must be shaken with 50mL of an aqeuous solution of Br2 in order to extract 95% of the Br2 from the aqueous layer.

Since you are extracting from the aqueous phase to the organic phase, you want 95% in your organic phase and 5% in your aqueous phase.