FL3 C/P #26, 58

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FL3 C/P #26, 58

Post by Amber9 » Thu Sep 05, 2019 2:39 pm

Q26 Can you explain the correct answer? I chose A thinking the anion will release protons

Q58 I am not sure what formula to use to solve for height when given pressure and density

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Re: FL3 C/P #26, 58

Post by NS_Tutor_Mathias » Mon Sep 09, 2019 6:16 pm

DI water clocks in at pH 7 (possibly lower in real life). It is the only option that would make the solution more acidic. Think of it this way: What would the pH of >any< buffer (or any solution) be if I added an infinite amount of DI water?

For A, recall that we are given 3 pKas for phosphoric acid. We know that around a pH of 12.3 half of those protons from Na2HPO3 would actually have dissociated. The opposite of what you predicted would happen: It would decrease the concentration of hydronium ions by abstracting protons until the solution is in equilibrium.

All options except D would increase the pH of the solution. Option C you can verify by just plugging this suggestion into the Henderson-Hasselbach equation and observing the shift in pH. If you want to give that a try, see how the pH changes as you shift the given ratio from option C from 1:1 to 10:1. PM me if you have that problem worked out!
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