I had plenty of citric acid around me when I was working as a pastry chef many ages ago. As Entropymancer said, it is a food additive and I used it to increase the acidity and sourness of sweets. Any citrus or lemony taste in sweets/candys virtually comes from the addition of citric acid in them nowadays. It should not be difficult to find it in grocery stores.
Some internet suppliers call it
Sour Salt. I am a bit wary of the name because it might actually be pure citric acid (which you want) or it could be sodium citrate (or calcium citrate) which you definitely do not want. Try
http://www.americanspice...21&WORDS=sour%2Bsaltas well as 2-3 more suppliers if in doubt that what they sell might be sodium citrate.
Upon arrival of the product you can just dissolve it in water; citric acid should give you a low pH (at the range of around 3) whereas sodium citrate is very slightly basic.
Need to calculate between salts and freebases?
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Need to calculate freebase or salt percentage at a given pH?
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