Acid and Base Neutralization

checking the pH (9K)

General rules

An acid or base may be neutralized and poured into the sanitary sewer only if the neutralized mixture is not toxic. The following is a list of acids and bases that may not be neutralized and disposed of to sanitary sewer:

  • Perchloric acid at any concentration
  • Nitric acid, concentrated
  • Sulfuric acid, fuming (concentrated)
  • Hydrofluoric acid (email chmwaste@uw.edu for information)
  • Acids or bases with high concentrations of metals or other contaminants
  • Acids or bases that contain dyes or surfactants
  • Any organic acids and bases that are still toxic after neutralization (most organic acids and bases - one exception is acetic acid with a concentration of less than 80%)

Please let us know that you are doing acid/base treatment by calling us at 206.616.5835 or emailing us at chmwaste@uw.edu. By law we are required to keep track of all hazardous waste treatment on campus. We can help you get set up. We will also be in contact with you yearly to see how you are doing and to collect your numbers for the year. In 2009, about 15 laboratories treated a total of over 1400 kg of acids and bases.


Dilute or weak acids

Wear protective clothing and eyewear and work in a fume hood if possible.

  1. Use sodium bicarbonate (baking soda) to neutralize the acid in a relatively large container. Add sodium bicarbonate slowly to minimize foaming. If the solution no longer foams when you add sodium bicarbonate, the solution is neutral (with a pH between 6 and 9).
  2. Note the volume treated in your Chemical Treatment Log, along with the date and your name.
  3. Pour the treated solution down the drain.

Concentrated strong acids

Concentrated acids have a concentration of 1 N or greater. Heat and fumes are generated during this procedure. Do this procedure in a fume hood with gloves, apron, and face shield. Proceed slowly and exercise extreme care to avoid severe burns and damage to your equipment. Use secondary containment in case of spills or overflow.

  1. You may opt to slowly dilute the concentrated acid 1 to 10 with cold tap water, adding the acid to the water. (Dilution is for your safety only and is not otherwise allowed during hazardous waste treatment.)
  2. Add 30 mg/L of trisodium phosphate (TSP) or 20 mg/l disodium hydrogen phosphate to the acid to buffer the solution. (This step is optional. It makes it easier to reach the endpoint without overshooting.)
  3. While stirring, slowly add 1 N sodium hydroxide to the mixture until the mixture reaches a pH between 6 and 9 (check the pH frequently with pH paper.)
  4. Note the volume treated in your Chemical Treatment Log, along with the date and your name.
  5. Pour the treated solution down the drain.

Dilute or weak bases

Wear protective clothing and eyewear and work in a fume hood if possible.

  1. Use citric acid to neutralize the base. Check the pH and add more citric acid until solution is neutral (with a pH between 6 and 9).
  2. Note the volume treated in your Chemical Treatment Log, along with the date and your name.
  3. Pour the treated solution down the drain.

Concentrated strong bases

Concentrated bases have a concentration of 1 N or greater. Heat and fumes are generated during this procedure. Do this procedure in a fume hood with gloves, apron, and face shield. Proceed slowly and exercise extreme care to avoid severe burns and damage to your equipment. Use secondary containment in case of spills or overflow.

  1. You can opt to dilute the concentrated base 1 to 10 with cold tap water, adding base to the water. (Dilution is for your safety only and is not otherwise allowed during hazardous waste treatment.)
  2. Add 30 mg/L of trisodium phosphate (TSP) or 20 mg/l disodium hydrogen phosphate to the base to buffer the solution. (This step is optional. It makes it easier to reach the endpoint without overshooting.)
  3. While stirring, slowly add 1 M hydrochloric acid to the mixture until the mixture reaches a pH between 6 and 9 (check the pH frequently with a piece of pH paper.)
  4. Note the volume treated in your Chemical Treatment Log, along with the date and your name.
  5. Pour the neutralized solution down the drain.