Description:

Sodium hydroxide solutions are available in nominal concentrations of 50% sodium hydroxide and 73% sodium hydroxide. The solutions are clear or slightly turbid, colorless or slightly colored, and when exposed to the air they absorb carbon dioxide forming sodium carbonate. The alkali equivalent of 100% sodium hydroxide is 77.5% sodium oxide.

Use:

Used for pH adjustment.

Purity Requirements:

The RMIC are based on a maximum dosage of 100 mg of sodium hydroxide/liter of water and are to be compared to impurity concentrations obtained by using sample proce dures described in this monograph. If the actual dosage is other than 100 mg/liter, the user is cautioned to consult Table 2 for appropriate RMIC values.

Bulk Sample Collection:

Sample in accordance with Standard for Sodium Hydroxide, AWWA B501-75, American Water Works Association, Denver, Colorado (1975).

Analytical Sample Preparation:

Weigh out 2.5 g of sodium hydroxide. In a 150-ml acid-washed beaker, dissolve the sample with 100 ml of deionized distilled water. Under a hood, acidify the solution with concentrated HCl to a pH of less than 2. Add hydroxylamine hydrochloride until the solution turns clear. Gently heat the solution to reduce the volume below 100 ml, making certain that it does not boil. Quantitively transfer to a 100-ml acid-washed volumetric flask and make to volume with deionized distilled water. Process a reagent blank by the same procedure.

Sample Analyses:

The analyses are to be performed on the sodium hydroxide solution in accordance with:

Standard Methods for the Examination of Water and Wastewater, 15th Edition, American Public Health Association, Washington, D.C. (1981).