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Buffered Solutions

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doreen:
Captain Joe, 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.(EX: if the pH of solution A is 3.47 and that of 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 25*C.

Solution A is 50.0 mL of a 0.100 M soln of the weak monoproctic 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?

AWK:
From hydrolysis of solution B you can calculate Ka (1.82.10-5).
Mixing solution A with 15 mL of 0.25 M KOH you will obtain buffer solution
with ratio: acid to salt=1:3 which shows pH=5.2.

Hope this is sufficient help to do all calculations.