How can you identify an unknown ph substance ?Watch
UI will give you a rough value.
A pH meter/probe will give you a value (assuming it has been calibrated properly).
If it is a strong acid, I'd do a titration to find the concentration and from that you can calculate the pH.
If it is a weak acid, you'd have to find both the concentration AND the value of the Ka, then do the calculations. If you know what it is, you can look up the Ka on Wikipedia.