Boric acid might refer collectively to three specific compounds: orthoboric acid [B(OH)3], metaboric acid (HBO2) and tetraboric acid (H2B4O7). However, the term “boric acid” generally refers specifically to orthoboric acid unless otherwise specified. Orthoboric acid is a solid, white powder at room temperature and is commonly used as an antiseptic, flame retardant and pesticide. It’s also used as a reagent for many reactions in organic chemistry and might be synthesized in the laboratory using several different methods.
Things You'll Need
- Boron nitride
- Filter paper
- Hydrochloric acid
- Orthoboric acid
- Sulfuric acid
Add an acid to an aqueous solution of borax (Na2B4O7) to form a salt and boric acid. Borax normally occurs with 10 water molecules attached to it (Na2B4O7.10H2O) in a compound known as a decahydrate. The following equation shows this reaction for hydrochloric acid: Na2B4O7.10H2O + 2HCl -> 2NaCl(aq) + 5H2O + 4B(OH)3.
Cool the solution produced in Step 1. The boric acid will drop out of the solution of salt water as solid, white flakes. Pour the solution through filter paper to obtain the boric acid.
Obtain boric acid through a similar reaction with sulfuric acid (H2SO4). The following equation shows this reaction: Na2B4O7.10H2O + H2SO4 -> Na2SO4(aq) + 5H2O + 4B(OH)3. The boric acid will drop out of the solution as before, which you can then separate by mechanical means.
Prepare boric acid by dissolving various other boron compounds in water. There are a variety of boron compounds that will eventually form boric acid by adding water. The following equation shows a typical reaction with boron nitride that produces ammonia as a byproduct: BN + 3H2O -> B(OH)3 + NH3.