Finding the Ka of a weak acid?

Question

I Just asked this answer and got some great responses. But what Im wondering is how do I find the Ka of a weak acid or base without any values?


Thanks in adavance. This type of questions always trip me up on tests. Basically Im being asked which of the following anions is the strongest base?
ClO-
ClO3-
ClO4-
Cl-
I-

How am I supposed to know? For reference Im studying pH & pOH.

Answer 1

Which anion is less electronegative...has the hardest time dealing with the negative charge?

(Can rule out Cl- and I-...cause HCl and HI are strong acids)

That leaves me with ClO-. Has only one oxygen...is the least electronegative.

Answer 2

Ka= ( [H+] [salt] ) / [acid]

N.B [X] means its concentration

for ur question, the strongest base is determined by charge density, i.e the amount of charge distributed on the diameter of the molecule, so a higher charge density means stronger base as it attracts H+ more, since -ve attracts +ve

so using data of the diameters of molecules and their charge u can find the answer.. i guess the answer is ClO4-

Answer 3

These are conjugate bases.

The strongest will come from the weakest acid. It is likely the ClO-. This is what bleach is made of,and it is a strong base