I. 

Title:  Which Bleach is the Most Effective Germ Killer for the Dollar.

Recommended Grade Level(s):  9-10

Subject(s):  Integrated Science and Biology

Author:  Dennis Zielinski

School:  Ellsworth Senior High

II.

Objective:  Students will collect data via titration of various bleach and ink solutions as evaluation tools to identify which bleach will be the most cost effective, along with being the best germ killer.

State Standards Met:

A.12.2

A.12.6

C.12.3

C.12.6

D.12.6

G.12.3

H.12.6

III

Equipment:

2- 10 ml graduate cylinders

2- Pipettes(Beryl or Eye droppers)

3-Test tubes

1-Test tube rack

3 x 5 index card

1.0 ml sample(s) of various bleaches

(diluted- 1 part bleach to 19 parts of water)

1.0 ml sample of washable blue ink

(diluted- 1 part ink to 19 parts of water)

Distilled water

Goggles

IV

Procedure:

1.  Fill one of the graduate cylinders with exactly 5.0 ml of water.

2.  Using one of the bleach pipettes, count the number of drops it takes to raise the

      level of the water from 5.0 to 6.0 ml.

3.  Record this value in the data table.  Make sure students hold the pipette straight,

     not on a slant, while dropping the bleach into the cylinder.

4.  Label this cylinder “Bleach”.

5.  Repeat steps 1-4, except this time use the second cylinder and count the number of

     drops of ink needed to raise the level of water from 5.0 to 6.0 ml.

    Then record this value in the table as well, and label this cylinder “Ink”.

6.  Using the “Bleach” pipette transfer exactly 1.0 ml of bleach from the “Bleach”

     cylinder to one of the test tubes.

7.  Fill the “Ink” pipette with “Ink” from the second cylinder.

8.  From your “Ink” pipette, slowly add the ink drop by drop into the bleach test tube.

     Gently shake the tube after each drop, and count each drop added.

9.  Students will be looking for a bluish colored endpoint.  This color may be faint,

     so they must proceed carefully.  The color change will start out brown and go to

     the blue color.

10. Record this number of drops in the table.

11. Repeat the experiment at least two more times

*

Calculations:

1.  Convert the average number of drops of ink into volume(ml) of ink used.

2.  Calculate the volume of bleach that will react with 100 ml of ink.  To compare dif-

     ferent bleaches, standardize the volumes of ink used.  Use the following ratios:

     no. of ml of ink/1.0 ml of bleach to  100ml of ink/X ml of bleach.

3.  Calculate the cost of bleach/milliliter.  Do this by dividing the bottle volume in ml

     by price in cents.

4.  Calculate the cost-effectiveness of the bleach.  Multiply calculation 2 by calcula-

     tion 3.

V.  Assessment