Question

Given the table of pKa values, at a pH of 3.5, which substance(s) exist predominantly in the non-protonated form? Please explain.

Answer 1

this is the table

Answer 2

ok. do i need to use the equation pH= pKa +log [A-]/[HA] to explain my answer. My teacher wants a detailed answer.

Answer 3

at the half equivalency point the pH is equal to the pKa. and we get more of the non-protonated form as we add more base until we get to the equivalency point where all of the acid is converted to non protonated form. pH will go up. the half way point between fully protonated and fully non protonated is the half equivalence point. if the pH is greater than the pKa, then acid is in non-protonated form. so do i need to find the pH?

Answer 4

I don't think so, unless you want the numerical proof

Answer 5

like, you would be better off using the equation

Answer 6

(also, made a typo before - higher pka means less protonation)

Answer 7

a small Ka value (much less than 1) means that the acid exists mostly in non-protonated form (denominator larger than numerator)

when we take the negative log of a small number (Ka to pKa conversion) then we get a positive number greater than 1. hence, the highest pKa value is the acid that exists mostly in non-protonated form

Answer 8

@Vocaloid Thanks.