A purified protein is in a HEPES (N-(2-hydroxyethyl)piperazine-N-(2-ethanesulfon
ID: 576396 • Letter: A
Question
A purified protein is in a HEPES (N-(2-hydroxyethyl)piperazine-N-(2-ethanesulfonic acid)) buffer at pH 7 with 800 mM NaCI. A sample (1 mL) of the protein solution is placed in a tube made of dialysis membrane and dialyzed against 1.0 L of the same HEPES buffer with 0 mM NaCI. Small molecules and ions (such as ) can diffuse across the dialysis membrane, but the protein cannot. a) Once the dialysis has come to equilibrium, what is the concentration of NaCl in the protein sample? Assume no volume changes occur in the sample during the dialysis. Number NaCl] = 1.8 mM (b) If the original 1 mL sample were dialyzed twice, successively, against 100 mL of the same HEPES buffer with 0 mM NaCI, what would be the final NaCl concentration in the sample? Number NaCl0784 mMExplanation / Answer
b)
Molarity M1 = 800 M
M2 = ??
volume V1 = 1 mL
final volume V2 = 100 + 1 = 101 mL
M1 V1 = M2 V2
800 x 1 = M2 x 101
M2 = 7.92 M
[NaCl] = 0.00792 mM