Re: What type of acid could I test antacids on?

There is not much of a choice when it comes to harmless acid, available as 
household material. The most commonly used one is the acetic acid, which 
is contained in the vinegar. Other options are the citric acid and the 
tartaric acid, which sometimes could also be found in the kitchen. The 
last two acids, however, are crystal compounds and should be dissolved in 
water prior to use.
The best way to test how much acid is neutralized by an antacid is to add 
some type of indicator to the antacid and then, with good stirring, to add 
drops of the acid until the indicator changes it's colour. At this point 
you should write down the amount of the used acid. This procedure is known 
as "titration" and is used by scientists to determine how much acid or 
base is contained in an object.
Finding a proper indicator at home could be difficult. The evolution of 
gas from some antacids, however, could serve as an indication of the 
neutralisation process - in such case the acid is added until the 
evolution of the gas stops. A typical example is the reaction, which takes 
place when you mix baking soda (a kind of antacid) and vinegar:

           NaHCO3 + CH3COOH ---> CH3COONa + H2O + CO2

The gas that evolves is carbon dioxide (CO2). I remember having a lot of 
fun with this reaction when I was a kid. :-)