Question

Ou have a 5 ml sample of a protein in 0.5 m nacl. you place the protein/salt sample inside dialysis tubing (see fig. 2-14) and place the bag in a large beaker of distilled water. if your goal is to remove as much nacl from the sample as possible, which would be more effective: (1) placing the dialysis bag in 4 l of distilled wa- ter for 12 h, or (2) placing the bag in 1 l of distilled water for 6 h and then in another 1 l of fresh distilled water for another 6 h

Answer 1

Procedure (2)

Step-by-step explanation:

Assume the dialyses come to equilibrium in the allotted times.

Procedure (1)

If you are dialyzing 5 mL of sample against 4 L of water, the concentration of NaCl will be decreased by a factor of

`(5)/(4000) = (1)/(800)`

Procedure (2)

For the first dialysis, the factor is

`(5)/(1000) = (1)/(200)`

After a second dialysis, the original concentration of NaCl will be reduced by a factor of

`(1)/(200) * (1)/(200) = (1)/(40000)`

Procedure (2) is more efficient by a factor of

`(40000)/(800) = \mathbf{50}`