# How do I calculate the pka of H2Se?

Relevance
• H2Se pKa .....

The obvious, which hardly deserves a post on YA, is to look up Ka of H2Se and take the "negative log". Keep in mind that there are two Ka's and two pKa's, although the second one is negligible.

Or it can be done experimentally. Use a pH meter to find the H+ ion concentration of a known concentration of H2Se.

H2Se(aq) <==> H+ + HSe^-

[H+] = 10^-pH

Ka = [H+][HSe-] / [H2Se] = [H+]²/[H2Se]

pKa = -log([H+]²/[H2Se])

• ...

look up the Ka for H2Se

I found Ka = 1.3E-4

then

pKa = -log Ka = -log1.3E-4 = 3.89

When you get a good response,

This is the only reward we get.

• usually a problem will give you a certain concentration of the acid. H2Se, and the pH of that solution. When you know those you can use the formula to calculate pKa

• You can't calculate it. It is determined by experiment. Data is available see the link for example:

https://en.wikipedia.org/wiki/Hydrogen_selenide

This gives a value of 3.89 ( scroll down the properties on the right hand side of the screen).

• pisgahchemist
Lv 7
6 months agoReport

Well, yeah. You can calculate pKa(1) from the experimental data. The hydrogen ion concentration of a known concentration of H2Se.