NS FL 2 Question - percent dissociation formula

[mariposas905]

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Why don't we use [F-] in the percent dissociation formula too? I thought this would be in the numerator along with the [H+] (because products over reactants right?)

See attached from next step practice exam FL 2, C/P section, Q16. I don't understand this part...

 

[PlsLetMeIn21]

You can use either F- or H+, but not both, in the numerator. They choose H+ because the question gave that to you. If the question had given the [F-] concentration, then they would have used it instead on [H+].

 

[mariposas905]

You can use either F- or H+, but not both, in the numerator. They choose H+ because the question gave that to you. If the question had given the [F-] concentration, then they would have used it instead on [H+].

But why don't we use both?

 

[PlsLetMeIn21]

Think of it as (amount of HF that dissociates)/(original amount of HF) x 100%. You get both an H+ and an F- when HF dissociates (equal amounts of each), so the 10-4 represents the amount of H+ and F- formed.

I'm not sure I'd worry about this question because it is unrealistic. 20 M HF is too high to be realistic and this topic has not shown up in any AAMC practice materials.

 

[mariposas905]

Think of it as (amount of HF that dissociates)/(original amount of HF) x 100%. You get both an H+ and an F- when HF dissociates (equal amounts of each), so the 10-4 represents the amount of H+ and F- formed.

I'm not sure I'd worry about this question because it is unrealistic. 20 M HF is too high to be realistic and this topic has not shown up in any AAMC practice materials.

Thanks for lmk! Also, wondering if you can help me with this Q since you seem to know a lot of info haha. In Kaplan's Biochemistry book, they say "Fermentation generates no ATP or energy carriers; it merely regenerates the coenzymes needed in glycolysis..." I get that it regenerates NAD+, but doesn't fermentation give out some ATP, but just a lesser amount? I thought it gives out 2 ATP, so I'm confused why Kaplan says "no ATP whatsoever."

From google, it says this: "The net energy gain in fermentation is 2 ATP molecules/glucose molecule. In both lactic acid and alcoholic fermentation, all the NADH produced in glycolysis is consumed in fermentation, so there is no net NADH production, and no NADH to enter the ETC and form more ATP."