Captain Kirk, of the Starship Enterprise, has been told by his superiors that only a chemist can be
trusted with the combination to the safe containing the dilithium crystals that power the ship. The
combination is the pH of solution A described below, followed by the pH of solution C. (Example:
If the pH of solution A is 3.47 and that of solution C is 8.15, then the combination to the safe is 3-47-
8-15.) The chemist must determine the combination using only the information below (all solutions
are at 25°C).
Solution A is 50.0 mL of a 0.100 M solution of the weak monoprotic acid, HX.
Solution B is a 0.0500 M solution of the salt NaX. It has a pH of 10.02.
Solution C is made by adding 15.0 mL of 0.250 M KOH to solution A.
What is the combination to the safe?
If, in preparing solution C, 15.0 mL of water was added instead of the 15.0 mL of KOH, what effect
would this have on the combination to the safe?
Show all calculations.
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