Plant pH Green Advice Lab

Materials (per group)

1 spot plate (w/ 12 wells)

0.1 M NaOH (sodium hydroxide-base)

0.1 M HCl (hydrochloric acid)

Distilled water


3 gms of plant part (leaves, or flowers, or roots, or stems) 1 mortar and pestle

20 ml alcohol

Small beaker

Paper towels

1 piece of white paper

electronic balance

Preparing the plant extract

1.      Zero (tare) the electronic balance with a weigh boat on top

2.      Add pieces of the plant material to the weigh boat until the balance measures 3 grams of plant material.

3.      Add the plant material to the mortar and begin to squash it with the pestle.  It need not be ground up, just smashed a bit.

4.      Add the smashed plant material to the 50 ml beaker.

5.      Add 20 ml of alcohol.  Let this sit for about 20 minutes while you prepare the spot plate serial dilution in the next section below. 

4- 1 ml pipettes

Preparing the spot plate: *Creating a SERIAL DILUTION*


6.         Use a clean pipette to place 18 drops of distilled water in wells #2 - #11. In well #1 place 20 drops of 0.1 M HCl and in well #12 place 20 drops of 0.1M NaOH. 


7. Using a clean pipette, transfer 2 drops of acid from the first well to the second well. Mix thoroughly by drawing up the entire contents of the second well into the pipette and then returning it to the well. Transfer one drop of the liquid from the second well to well 3, mixing as before and continue in this way up to well #6 which will be the last one of the acidic dilutions.

8. Repeat this procedure for the other rows. Using a clean pipette, repeat the dilution procedure using the 0.1 M NaOH (2 drops)  in the same row as the acid dilution, but working backwards from #12 to #8, making #8 the last of the basic dilutions. Do not add anything to well # 7.

9. Each well has been diluted by a factor of 10. In well #1, the [ H+ ] = 1 x 10-1 mol/liter, in well #2, the [ H+ ] = 1 x 10-2 mol/liter. In well #12 the [ OH- ] = 1 x 10-2 mol/liter, in well # 11 the [ OH- ] = 1 x 10-3 mol/liter.

10. Return now to your plant extract.

11. Tilt the liquid back into a small beaker

1. Use a clean pipette to draw up a full 1ml of the plant extract.

12. Now return to your spot plate/serial dilution.

13. Place the spot plate/serial dilution on a piece of white paper.

18. Add 2 drops of the plant extract to each of the spot plate wells. 

19. Observe the colors.

20. Clean up.  Thoroughly rinse the spot plate, mortar and pestle, funnel, beakers and turn them upside down on a piece of paper towel at your lab bench.  Throw the used pipettes in the trash along with the used paper towels.  Return the acid and base containers, as well as the distilled water and alcohol to the teacher’s lab bench.