You can prepare boric acid in a laboratory setting by reacting borax with sulfuric acid following a specific procedure.
Preparing Boric Acid from Borax
Boric acid ($H_3BO_3$) can be synthesized by the reaction of sodium tetraborate decahydrate (borax, $Na_2B_4O_7 \cdot 10H_2O$) with a strong acid like sulfuric acid ($H_2SO_4$). The process involves dissolving the borax and then adding the acid to precipitate the less soluble boric acid.
Here is a method based on the provided reference:
- Start with Borax: Begin with approximately 5 grams of borax.
- Dissolve the Borax: Dissolve the borax in a beaker using the minimum amount of water necessary. Do not use more than 100 mL of water. Using the minimum amount helps concentrate the solution, which aids in the precipitation of boric acid later.
- Filter (If Needed): If there is some undissolved material after adding the minimum amount of water (up to 100 mL), remove it by filtering into another beaker. This ensures you are working with a clean solution of dissolved borax.
- Add Sulfuric Acid: Slowly add 1M sulfuric acid (which is approximately 5% $H_2SO_4$) to the borax solution while stirring. Adding the acid slowly and with stirring is crucial to control the reaction and ensure complete precipitation of the boric acid.
As the sulfuric acid is added, a white precipitate of boric acid will form. The reaction is typically represented as:
$Na_2B_4O_7 \cdot 10H_2O + H_2SO_4 \rightarrow 4 H_3BO_3 + Na_2SO_4 + 5 H_2O$
After adding the acid, the mixture is usually cooled to maximize the yield of boric acid, as its solubility decreases significantly with lower temperatures. The solid boric acid is then separated from the solution by filtration and can be purified by recrystallization.
