NEUTRALIZATION OF SELECT ACIDS & BASES

 

Neutralization of strong acids and bases can reduce the size of your laboratory's aqueous waste stream. Neutralization is the most efficient and least costly way of managing waste acids and bases. After neutralization, waste liquids can be disposed of to the sanitary sewer.

 

Solutions That Should Not Be Neutralized

 

Acids that are very reactive with water should not be neutralized, unless you have expertise in handling them. These include: acid anhydrides and chlorides; chlorosulfonic acid, fuming nitric and sulfuric acids; liquid halides of boron, silicon, tin, titanium and vanadium; and liquid halides and oxyhalides of phosphorus, selenium and sulfur. Due to safety considerations, you should not attempt to neutralize hydrofluoric acid.

 

Personal Protection and Equipment

 

Carry out neutralizations in a well-ventilated fume hood. Use the sash or a safety shield for protection against vigorous reactions. Wear a chemical resistant apron, splash-proof goggles or a full-face shield and nitrile gloves. Long gloves or gauntlets are also recommended. A five gallon polyethylene bucket is recommended for neutralizing 1-10 liters. A large container is needed in acid neutralization for addition of ice and base, and to safely stir the reaction.

 

PROCEDURES

 

Neutralization of Strong Bases
  1. Bases that may be neutralized include: solutions of potassium and sodium hydroxides, alcoholic sodium or potassium hydroxide cleaning solutions, ammonium hydroxide and ammonia solutions.
  2. Dilute the base to a 5% (by weight) concentration or less.
  3. Slowly add 6 N hydrochloric acid or other acid.
  4. Monitor pH changes with pH meter or pH paper. (Note: Liquid indicators can oxidize rapidly in basic solutions and give false color change).
  5. When pH is between 6 and 9, solution can be washed down sanitary sewer with 20 parts water.

 

Neutralization of Strong Acids

1.    Prepare a 6 N solution of sodium hydroxide (240 g/L) or potassium hydroxide (336 g/L).

2.    One liter of 6 N base can neutralize:

 

Acid

Qty. (mL)

Acid

Qty. (mL)

Acetic (glacial)

342

Nitric (70%)

378

Formic (88%)

264

Perchloric (70%)

516

Hydrochloric

504

Phosphoric (85%)

414

Hydrobromic (48%)

720

Sulfuric (96%)

166

Hydriodic (47%)

1080

Trichloroacetic (20%)

4902

 

3.    Dilute the acid to a 5% (by weight) concentration or less (add acid to water, NOT water to        

        acid).  Use ice as necessary to cool the solution. Limit the solution to a maximum of 10

        liters.  Acids may generate heat upon neutralization.

4.    Neutralize with 6 N sodium hydroxide or potassium hydroxide, adding it slowly.

5.    Monitor pH with pH paper, a pH meter, or a suitable indicator.

6.    When pH is between 6 and 9, wash solution down the sanitary sewer using 20 parts water.