Acid Bath

SAL (Sustainable Agricultural Landscapes) Laboratory Protocol:

Author(s): Gabriel Maltais-Landry, Katie Neufeld, & Paula Porto

Last updated: May 23, 2018

- Objectives

- Materials

- Step by Step Description

**Metal vessels can not be acid washed!

Objectives:

An acid bath is a solution of approximately 5% HCl and water. It is used to clean glassware and plastic sample containers for re-use. Read this protocol before using or regenerating the acid bath(s).

Materials:

To Use:

- Dirty labware (non-metal only!)

- Long neoprene or butyl gloves

- Lab Coat

- Protective Glasses

- Closed-Toed Shoes

To Regenerate:

- Concentrated HCL(37%)

- Sodium Bicarbonate

- Nitrile or neoprene or butyl gloves

- pH strips

- Fume hood

- Distilled water

Step By Step Description:

How to use the Acid bath:

1. You should be wearing long neoprene or butyl gloves, lab coat, protective glasses, closed-toed shoes, and pants before working with the acid bath.

2. Labware to be acid-washed must be thoroughly rinsed with tap water to remove soil residues and/or nutrients. Avoid metal and aluminum.

3. Drain excess tap water before putting labware in the acid bath.

4. Add labware and fill individual items with liquid while avoiding to make bubbles. Plastic might float even when full.

5. Usual soaking time is 16 hrs (overnight). The minimum soak time is 4 hours, if time is limited or throughput must be high.

6. When removing labware from the acid bath, allow the acid to drain back into the bath, then put items in a clean tub before rinsing.

7. Rinse labware 3 times with distilled water, then put on drying rack

8. Once labware is dry, store in the cabinet above the sink, with a piece of aluminum foil to protect the opening whenever possible. Make sure to close the glass doors of the cabinet.

Priority items for acid bath: bechers, graduated cylinders, volumetric flasks, containers for solution, funnels.

To Make A New Acid Bath:

9. You must be wearing closed-toed shoes, long pants, a lab coat, protective glasses, and gloves before changing the acid bath. No exceptions. Wearing an apron is recommended.

10. Dump the old acid bath into an appropriate disposal container. If acceptable by UBC, you can neutralize it with sodium bicarbonate (baking soda) - it will make bubbles (CO₂ outgassed from the re-equilibration of carbonates at low pH). Test if your waste solution has reached neutrality (pH = 5.5-10.5) by using a pH strip, and dispose of it down the drain with copious amounts of water.

11. Rinse the tub with deionized water several times. Make sure that there are no more soil residues.

12. Fill the tub to the 18L mark with deionized water, and place it under the fume hood. You can elevate the sash above the recommended height if it helps you to safely place the tub on the counter. Remember to lower the sash to the recommended level before proceeding to the next step.

13. Under the fume hood, add 1L concentrated HCl (37%) to the water, not the other way around (if you add water to concentrated HCl, the first drops of water will heat up and evaporate, possibly carrying acid droplets towards your face/skin). Make sure the lid is nearly closed when pouring the acid, and that the lid is closed immediately after pouring (fumes are created when acid is added to water).

14. Wait for fumes to disappear before adding deionized water to reach the 20L mark (final volume).

15. This is referred to as a “5% HCl acid bath” even though the actual HCl content is 1.85% (i.e. 37% / 20).

16. You can make different volumes, as long as the dilution remains 1:20.