Question

What does the symbol ka mean in chemistry?

Answer 1

 Ka is an equilibrium constant for the partial ionization of "weak" acids in water.

Answer 2

Ka is an equilibrium constant for the partial ionization of "weak" acids in water. If such a weak acid is HOAc, the ionization is 
HOAc = H+ + OAc- 
and Ka= [H+][OAc-]/[HOAc] 

Ka values range from about 10-2 to 10-14 Greater than 10-2, they are essentially strong acids, and below 10-14, they produce no more [H+] in water than would normally be observed.