This was just a curiosity thing, but... I assumed "5% acidity" to mean 5 percent of the soln was acetic acid, by volume (though, doing the calculations for "By mass", I got roughly the same pH). Also, I couldn't find the density of acetic acid in my text book, so I assumed it was close enough for my calcs to water to use water's density. The pH I figured was ~ 2. Anyone know if this is correct? Also, I'm using vinegar to clean my apartment before I leave... and some of my oven stains aren't coming off using it right out of the bottle. I saw that the boiling point for acetic acid was about 20 degrees C higher than water, so I'm wondering if boiling vinegar in a sauce pan w/o something to catch the vapor will increase the pH enough to make it a stronger cleaning agent. Anyone else ever try this?