Hi, I've got this question where I have to describe two methods of measuring the pH of a substance. I've already got the one using electrochemical potentials, but I'm a bit stumped on the second method. What I've said is to carry out a titration with an alkali until the solution is neutralised. One can then work out the concentration, and if the acid fully dissociates, it's pH. However this is a bit of a fudge as it doesn't work for anything but strong acids. Is there a better way to do this? Also, I have a second question where I have to devise an experiment to measure the eqilibrium constant Ka of a weak acid. I've written that a number of solutions of the acid could be made, each with a different concentration (increasing linearly from, say, 0.01moldm^-3 to 1moldm^-3), and then dumping some methyl orange in the substance and seeing at which concentration the colour just changes to orange. This substance should be at a pH of 4, so the concentration of H+ ions can be determined and if the concentration of the original substance is already known (this could be measured from a titration I guess) then Ka can be determined. But again this is a bit of a manky method because methyl orange switches at a range of pH values, not just 4. Does anybody have a better method? Cheers, Just some guy.