Question

A student is preparing a solution of 0.1 M Tris-Cl (pH 7.0) with 200 mM NaCl. To adjust the pH, the student started with concentrated HCl and overshot, reducing the pH to 4.0. To correct this, the student added NaOH until the pH reached 7.0 and then brought the solution to volume. Which of these statements describes the prepared buffer?
a. The buffer is correctly prepared.
b. The pH is not accurate because both acid and base were used.
c. The pH is accurate, but the solution will have excess salt.
d. The pH is accurate, but the concentration of Tris will be incorrect.
e. The pH is accurate, but the volume will be too high.

Answer 1

Answer:

The correct statements are C The pH is accurate but the solution will have excess salt. D The pH is accurate but the concentration of Tris will be incorrect

Explanation:

As the pH is finally maintained at 7 the pH for the buffer solution will be accurate but excess salt will be produced due to use of Both NaOH and HCl to make up the to 7.

As more volume of water is required at final step to make up the volume the concentration of tris will be incorrect.