Solving for the Safe Combination: pH of Solutions A & C

[chjopl]

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, which consists of four numbers, 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 find the combination using only the information below. All solutions are at 25EC.

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 0.225 M KOH to solution A.

What is the combination of the safe?

Hint: You don't need to know the identity of X, except that the X in solution A is the same as in solution B.

 

[Sirus]

Please do not double post. I have responded in the homework forum.

 

[ravenprp]

The combination to the safe would be 3-47-8-15. This is because the pH of solution A can be calculated using the Henderson-Hasselbalch equation, which takes into account the concentration of the acid and its dissociation constant. The pH of solution C can then be calculated by taking into account the amount of KOH added and the volume of the solution. By using these calculations, we can determine the pH of both solutions A and C, and therefore the combination to the safe. It is important to note that the identity of X is not needed, as it is the same in both solutions A and B. Therefore, Captain Kirk can trust the chemist to find the safe combination and access the dilithium crystals to power the Starship Enterprise.