pH/HH question

[drillers]

Biochemical reaction is taking place in a 0.1M Buffer. The initial pH is 7.4 , and the pka of the buffer is 7.2. If, in a final reaction volume of 1.0 mL, 10-micro mol of protons are generated, what would be the final pH of the solution?

7.59
7.25
7.22
7.20
7.15


Well, ph=pka + log (base/acid)... so 7.4=7.2 + log (x/y)

so 0.2 = log (x/y)

I honestly have no idea where to go with this, I know there is a final reaction volume but yeah I got no clue how to find the new ph.... please help

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[labqi]

I am

Biochemical reaction is taking place in a 0.1M Buffer. The initial pH is 7.4 , and the pka of the buffer is 7.2. If, in a final reaction volume of 1.0 mL, 10-micro mol of protons are generated, what would be the final pH of the solution?

7.59
7.25
7.22
7.19
7.14


Well, ph=pka + log (base/acid)... so 7.4=7.2 + log (x/y)

so 0.2 = log (x/y)

I honestly have no idea where to go with this, I know there is a final reaction volume but yeah I got no clue how to find the new ph.... please help

Doing this from my phone but forgive me if I'm incorrect. So you have a .1 molar buffer thus: ratio = 1/10. If you add more protons: the acid will increase by 10+(moles of h added/volume) and the base decreases by 1- (moles of h added/volume). Something like that maybe?

 

[Czarcasm]

Based on the question, you can assume that as the reaction proceeds, it's becoming more acidic (because there's an excess of protons). This rules out choice 1: 7.59. Also, because the question also tells you have an excess of protons, you can basically assume that the buffering capacity has been exceeded (a functional buffer would neutralize excess protons) and therefore, we should anticipate that the pH should be lower than the buffering capacity (7.2). This rules out choice 2: 7.25. The only answers available under 7.2 are 7.19 and 7.14. It would take a considerable amount of protons to drop 1 pH unit. 1.0mL 10-micro mol is essential 1 nanomol of protons ...barely anything so you can reasonably assume that the pH is very close to but slightly under the pH of the buffering capacity. 7.19 is the best answer.

 

[drillers]

That's exactly what I thought... the answer though that the book gives is C which is 7.22... I have no bleeping idea how they get this because I also thought that the answer had to be at or below the buffer ph of 7.2. How the heck are they calculating 7.22? What am I missing?