Flow tests using safe acids and bases and an indicator

I want to conduct some visualization tests on a new mixing device. I would like to mix acid with base and use an indicator to see a color change. These are flow tests and the flow rates of acid and base will be equal. I'd like to only use a stoichiometric excess of 20% of either the acid or base.


Since I will be conducting these experiments in my basement, I'm thinking I should probably try to use acids and bases that are safe to humans. I suppose I could use a 0.001M concentration of HCL and NaOH. But I'd be handling more concentrated solutions prior to dilution to these concentrations.


I could maybe use something like baking soda for the "base" and vinegar for the "acid". Since these are weak, there will be equilibrium shifts during the reactions in order to use up all of either the acid or base (depending upon which reactant is the 20% excess). I need the reaction to be very rapid such that the several microsecond mixing that I am expecting will be rate controlling.


Any suggestions for acids/bases and indicator that I might use? A strongly colored indicator in the weak acid or base would be strongly preferred. It would be best if after reaction, that indicator was colorless or an opposite color prior to reaction (red or blue converting to yellow). Again, please note that the flowrate of acid will be identical to that of base (around 0.2 gpm) except that either the acid or base will have a molarity that is 20% higher than the other reactant.


Thanks.


