Citric acid is available as a monohydrate and in anhydrous form. Anhydrous means there is no water, so the citric acid is more powdery than the monohydrate form that has water.Anhydrous citric acid is usually used in bath bombs, but the monohydrate form will also work.
Unless the project specifies the use of one form over the other, either one should work.
 Anhydrous citric acid may be available in the soap making section of craft stores as it is a common ingredient in fizzing bath bombs. Call the store before going there to make sure they have the quantity in stock you need.
 A chemical supply source will provide the greatest number of options in terms of grade, texture, quantity and form. Read through your supplier's definitions of the grades they sell. Many suppliers also create their own grade labels to indicate the quality of the chemical. Citric acid is available in different grades including:


Food Chemical Codex (FCC)- food gradeAmerican Chemical Society (ACS) grade- the substance meets the standards set forth by the ACS for reagent chemicals in their publication.United States Pharmacopeia (USP) grade- a substance that meets the specifications in the "Reagents, Indicators and Solutions" section of the USP.
Choose which form of citric acid you want to purchase.
Check craft stores for citric acid.
Buy citric acid through a chemical supply company.
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