The mass of a proton is equal to the mass of?

It is about equal to the mass of the neutron. So, most people just say that they have the same mass.

*Hope that helps and enjoy :)*

The answer would be neutron. Well, they do not have the exact same mass, only a difference of about 0.98 or even less than that. So they are counted as equals. 

False, it's not only for acids. I've put alkalis and phenolphthalein (an indicator that goes colourless in the presence of acid) into the beaker and had an acid in the burette.

What a titration actually does is calculates the exact amount of one solution that reacts with a different one.
Whatever happens, you need to know the substances are pure, and the concentration/volume of the substance in the burette.