Saponification value of beeswax

The number of milligrams of potassium hydroxide (KOH mg/g) required to saponify 1 g of beeswax. It is one of the quality indicators of beeswax. For example, the more components that can be saponified in beeswax, the higher the saponification value and the better the quality; on the contrary, the more impurities, the lower the saponification value and the poorer quality.

Determination Of Saponification Value

1. OUTLINE OF THE METHOD

The wax is saponified by refluxing with a known excess of alcoholic potassium hydroxide solution. The alkali consumed for saponification is determined by tiltrating the excess alkali with standard acid.

2. APPARATUS

2.1: Conical Flasks — 250 mL to 300 mL made of alkali resistant glass.

2.2: Reflux Air Condenser — At least 65 cm long.

3. REAGENT

3.1: Methyl Ethyl Ketone — Stored in a dark place.

3. 2: Rectified Spirit — Neutral to phenolphthalein indicator.

3. 3: Alcoholic Potassium Hydroxide Solution — Dissolve 30 g of potassium hydroxide in rectified spirit and make up to 1 litre. Allow to settle overnight in a dark place, decant the clear liquid and keep in a bottle closed tight with a cork or rubber stopper.

3. 4: Phenolphthalein Indicator Solution

3. 5: Standard Hydrochloric Acid — 0.5 N.

4. PROCEDURE

4. 1: Weigh accurately about 2 g of the wax in a tarred conical flask.

4. 2: Add 25 mL of methyl ketone, followed by 25 mL of alcoholic potassium hydroxide solution.

4. 3: Add a few pieces of pumice stone and connect the reflux air condensed to the flask.

4.4: Heat the flask on a water-bath or electric hot-plate for about 2 hours.

4.5: Boil steadily but gently.

4.6: After the flask and condenser have cooled, wash down the inside of the condenser with about 10 mLof rectified spirit.

4.7: Add about 1 mL of phenolphthalein indicator solution and tiltrate with standard hydrochloric acid.

4.8: Carry out a blank determination at the same time