ACIDS, NEUTRAL, BASES

AN INVESTIGATION USING INDICATORS

PROBLEMS: 1. Determine if unknown solutions : A, B, C, D, E, G, H, & I are acids, neutral, or bases.

2. Explain in your own words how indicators work and are used.

8th Grade Science Standard: 5e. Students know how to determine whether a solution is acidic, basic, or neutral.

MATERIALS: 8 unknowns, 8 test tubes and holder, litmus paper, bromothymol, phenolthalein, phenol red, pipette and bulb

PROCEDURE:

1. Wear goggles and wash hands if any solution should spill on hands.

2. Label 8 test tubes with unknown letters

3. Pipette 3ml of each unknown solution into eight test tubes with correct label

4. Cut one piece of litmus paper into thirds, put litmus paper into (8) tubes

5. Record observations and clean tubes

6. Pipette 3ml of each unknown solution into eight test tubes

7. Add 1-2 drops of phenolthalein to the eight test tubes

8. Record observations and clean tubes

9. Pipette 3ml of each unknown solution into (8) test tubes

10. Add 1-2 drops of bromothymol to each test tube

11. Record observations. Do not clean tubes

12. Compare observations with the indicator chart to determine if unknown is acidic neutral or basic

13. Copy and fill in chart with an x for each solution you believe to be either acid, base, or neutral.

14. Add 1-2 drops of phenolthalein to the eight test tubes with bromothymol blue.

15. Clean test tubes. Do the same procedure for phenol red as you did in the previous steps.

16. Record observations and clean tubes

17. Fill in the colors on the indicator chart for phenolthalein and bromothymol. Do this also for phenol red.

DATA:

WRITE DOWN COLOR OF INDICATORS BEFORE YOU BEGIN

______

Red litmus Blue litmus phenolthalein bromothymol blue phenol red

INDICATOR / ACID / NEUTRAL / BASE
Blue pH LITMUS / RED / BLUE / BLUE
Red pH LITMUS / RED / RED / BLUE
PHENOLTHALEIN / COLORLESS / COLORLESS / PINK/MAGENTA
BROMOTHYMOL / YELLOW / GREEN/BLUE / BLUE
PHENOLTHALEIN & BROMOTHYMOL / * / * / *
PHENOL RED
/ * / * / *

*Fill this in from your observations from your data

WRITE IN THE COLOR YOUR SEE-

UNKNOWN / Blue litmus / Red litmus / Phenolthalein / Bromothymol blue / Bromothymol blue & phenolthalein / Phenol red
A
B
C
D
E
G
H
I

Fill in the chart with an (x) for each solution you believe to be either an acid, base or neutral.

UNKNOWN / ACID / BASE / NEUTRAL
A
B
C
D
E
G
H
I

QUESTIONS:

1.  Look at your results. Do your results agree with your findings from all the other tests or do you have discrepancies? For example, all the unknowns you think are acids should be the same colors for each different indicator that represents an acid, are they? If not, what’s wrong?

2.  How were indicators used in this lab? Be detailed in your explanation. Explain how indicators work. How do they change color and why?

3.  DRAW PICTURES for all 6 indicators showing what they look like in the presence of a base, an acid, and neutral. There should be a total of 18 pictures in COLOR, labeled.

Short Conclusion