Name ________________
LAB# ________________
What do Indicators Indicate?
Background:
Indicators are chemicals that tell us more about things than we can normally see.
Most Indicators do this by changing color when they are mixed with specific solutions.
Litmus paper, for example changes form blue to pink when combined with an acid, and
from pink to blue when combined with a base. By using indicators, we can tell if a
certain substance is present.
Indicators can also tell us if something is living. Living things must do certain
things to survive, like eliminate metabolic waste. Indicators, by their color change, can
tell us if something is getting rid of CO2 or giving us liquid waste.
In this lab you will observe the color changes that occur when different
substances are exposed to indicators. You will then be able to determine what those
substances contain.
PART 1:
1. Obtain one dropper bottle containing each of the following indicators: phenol red,
Bromthymol blue, benedicts solution, Lugol’s iodine.
2. Obtain one vial of each pink and blue litmus paper.
3. Obtain a depression tray. Following the diagram below, place 10 drops of each
indicator into the respective wells.
Key
Base
PR
BB
LI
P
PR = Phenol red
Acid
PR
BB
LI
P
BB = Bromthymol blue
LI = Lugol’s iodine
Starch
PR
BB
LI
P
P = phenolphthalein
4. Using droppers, add two drops of base to each well in the first row. RECORD
YOUR OBSERVATIONS INTO TABLE 2. DO NOT LET THE DROPPER
TOUCH THE INDICATOR!!
5. Place two drops of acid into each well in the second row. RECORD YOUR
OBSERVATIONS INTO TABLE 2.
6. Place two drops of starch into each well in the third row. RECORD YOUR
OBSERVATIONS INTO TABLE 2.
PART 2 – Testing for sugar
1. Pour 25 mL of Benedict’s solution into three different beakers.
2. Place one of the three items that your teacher gives you to test for sugar.
REMEMBER which beaker has which substance!
3. CAREFULLY place the beakers onto a hot plate and heat for 5 minutes.
4. Note any color changes and record them into table 3.
PART 3 - Testing for CO2
1. Place 15 mL of Phenol red, Bromthymol blue, phenolphthalein, and Lugol’s iodine
into an Erlenmeyer flask.
2. Using 4 different straws provided by your teacher, blow into the flasks for 2 minutes.
3. Record and color changes in table 4.
PART 4 – Testing acid’s and bases with litmus.
1. In the front of the room, you will see 4 beakers labeled 1, 2, 3, and 4. Each beaker
has a different substance.
2. Using your litmus paper, determine if each substance is an acid or a base.
3. Record your data on table 5.
Post lab QUESTIONS
1. Did more than one indicator test for the same substance? If so, which indicator(s)
were they and what did they test for?
2. What gas do living animals give off when they breathe? What indicators should we
use to determine if an animal is alive?
3. Urine has a pH of 4. Which color litmus paper could you use to test if something is
giving off urine? Why?
4. Are there any other indicators that you could use to check for the presence of urine?
What are they?
5. If you wanted to eat food to give you lots of energy, which food that you tested would
you select and why.
Table 1
Indicator
Tests for
Color changes from…
Color changes to…
Phenol red
Bromthymol blue
Pink litmus
Blue litmus
Lugol’s iodine
Benedict’s solution
Phenolphthalein
Table 2
Substance
WATER
BASE
ACID
STARCH
Phenol Red
Bromthymol Blue Lugol’s Iodine
Phenolphthalein
Table 3
Substance
Color of benedicts before
Table 4:
Indicator
Before CO2
Color of benedicts after
After CO2
Phenol Red
Bromthymol Blue
Lugol’s Iodine
Phenolphthalein
Table 5:
Substance
Color change
with Blue
litmus? (+/-)
Color change
with Red
Litmus? (+/-)
The substance
must be? (acid,
base, neutral)
Actual pH?