Preparation of Boric Acid
Objective: To prepare boric acid from borax.
Apparatus/Glassware Required: Conical Flask, Beaker, Measuring Cylinder, Funnel
Chemicals Required: Borax, Nitric acid, Distilled water
Principle: It is a weak mineral acid that is water soluble at room temperature. It occurs in nature as a mineral sassolite in volcanic fumaroles and hot springs. It is also found in sea water, plants, and fruits in small amounts. It is prepared by the reaction of borax (a natural mineral) with acid like nitric acid or hydrochloric acid or sulphuric acid. Nitric acid is preferred to hydrochloric acid because sodium nitrate is more readily soluble than sodium chloride. Sulfuric acid is not employed because it is not so readily washed out.
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Procedure: Dissolve 10 g of borax in 25 mL of boiling distilled water, and filter while hot. 5.4 g of nitric acid (a slight excess of nitric acid is necessary) add to the hot filtrate and the reaction mixture is set aside in a cold place for a day. The next day the crystals of boric acid are collected by filtration and wash with a small quantity of cold distilled water. Boric acid is purified by re-dissolving the washed crystals in 20 mL of boiling distilled water. The solution is cooled and kept until no crystals of boric acid appear. Boric acid crystals are filtered and dried yielding 50-60% colorless or white, pearly, lamellar crystals, somewhat unctuous to the touch; taste feebly acid, slightly bitterish.
Uses: Boric acid is non-toxic with antibacterial properties, and it is mainly used as an antiseptic agent, acne treatment, preservative, insecticide, pH buffer, swimming pool chemical, flame retardant, and a precursor to many useful chemicals. It is used industrially for the manufacture of fiberglass, household glass products and the glass used in LCD displays.
1. Physical properties: Boric acid is a white crystalline solid with a density of 1.435 g/mL, melting point of 170.9 °C and boiling point of 300 °C.
2. properties: Boric acid is a weak monobasic acid, and is considered a Lewis acid. It dissolves in boiling water and in anhydrous sulfuric acid. When heated to high temperatures (over 170 °C), it undergoes dehydration to form metaboric acid (HBO2): H3BO3 → HBO2 + H2O
3. Health hazards: A low concentration of boric acid does not pose any toxicity. However, boric acid is poisonous if swallowed or inhaled in large quantities. Therefore, its container should bear the warning “Not for internal use”. High concentrations of boric acid can potentially lead to reproductive problems. Exposure to boric acid over long periods of time can cause possible kidney damage.
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Last Updated : 26-07-2018 02:52:34 pm
Madhusudhana Reddy Induri
Dr. Reddy working as Associate Professor, Department of Pharmaceutical Analysis, KVSR Siddhartha College Pharmaceutical Sciences, Vijayawada