The detection method of sodium hydroxide

The sodium hydroxide in stock should be tested at least once a quarter. Since sodium hydroxide is stored for too long, the surface will react with carbon dioxide in the air, so it is necessary to test the content of its active ingredients. After the sodium hydroxide sample is fully dissolved, it is titrated with standard hydrochloric acid solution, and at the same time, phenolphthalein is used as an indicator to determine the content of the active ingredient of sodium hydroxide. The test method is as follows:

(1) Take a clean weighing bottle of known weight, add about 20g of solid sodium hydroxide, close the lid tightly and weigh; then measure about 40mL of sodium hydroxide solution with a graduated cylinder and pour it into the weighing bottle. Then transfer the sample into a 500mL conical flask, rinse the weighing bottle with distilled water 3~4 times, add about 100mL distilled water, slowly shake until all dissolved, dilute to about 400mL, cool to room temperature, and mix well.

(2) Pipette 50mL of the test solution into a 250mL conical flask, add 5 drops of phenolphthalein indicator, titrate with 1mol/L hydrochloric acid solution until the red color disappears, record the volume of hydrochloric acid consumed, and then add methyl orange Two drops of indicator solution, continue to titrate with 1mol/L hydrochloric acid until the solution changes from yellow to orange, record the volume of hydrochloric acid consumed at this time.