help with a chemistry problem?

Question

the pH of a 0.063 M solution of HBrO is 4.95. Calculate Ka.

Answer 1

You can polish this up. I don't have my slide rule available. pH indicates [H+] is about 10-5 moles. The equilibrium is
[H+][OBr-]/[HOBr]= Ka
Here [OBr-] is also 10-5
Since 10-5 is quite small compared to 0.063, the loss of HOBr in the formation of the ions can be ignored.
Then (1x10-10)/(.065)=Ka, which would be about 1.5x10-9