Name:
Period/Block:
Date
It’s to Dye For!
Lab: pH, Indicators, Acids and Bases
Learning Target: I can create three natural dye solutions – one acidic dye, one basic dye
and one neutral dye.
Part A: Pre-Lab Questions
Please answer on a separate sheet of paper using complete sentences. Be sure to attach the pre- and postlab questions to your lab sheet.
1.
2.
3.
4.
Define and give an example of an acid.
Define and give an example of a base.
Make a Hypothesis: Why might someone want (or need) to distinguish an acid from a base?
Create a flow chart of your procedure, including pictures/diagrams for each step.
Part B: Making and Using a Natural Dye
Materials:
 9 pieces of white 50 cm long wool yarn.
 1 can Spinach
 10 g Onion skins
 1 Beet (fresh)
 1 Carrot (fresh)
 3 – 250 mL beakers
 100 mL Vinegar (CH3CO2H) or
Hydrochloric acid (HCl)
http://braukaiser.com/wiki/images/c/c0/Red_cabbage_pH_series.jpg
 100 mL Baking soda (NaHCO3) or
Sodium hydroxide (NaOH)
 Hot water
 Glass stirring rod
 Strainer
Procedure:
1. Chop up your plant material into small pieces and
place them in boiling water for about 30 minutes.
When you have reached your desired color, be sure to
strain your plant material out.
Name:
Period/Block:
Date
2. Determine the pH of the solution using a universal pH
indicator.
3. Use vinegar and/or baking soda to make the solution
more acidic or basic. Note: You must create three
distinct color dyes of all different pH.
4. Place three pieces of yarn into each solution for 15
minutes.
5. Use a stirring rod to remove the yarn from the dye
solution.
6. Dry the yarn on a paper towel and attach it to the chart
with tape.
My plant material:
Physical Observations:
Example: Red cabbage, onion
skins, spinach, beet, carrots, etc.
Example: Color should be noted, how fibrous the plant material is,
how quickly the color leeches from the plant when immersed in
water, etc.
Additional Observations:
Students may write any additional observations they make during the lab.
Results:
Example calculations
Acidic Solution
Basic Solution
Neutral Solution
Amount and type of
Acid/Base Added
7 mL = 0.007 L
of HCl
15 g of NaOH
0L
Name:
Period/Block:
Date
Molar Mass of
Acid/Base
36.6 g/mol HCl
58.5 g/mol NaOH
n/a
Moles of Acid/Base
Added (assume STP)
0.01005 mol HCl
8.54 x 10-2 mol HCl
n/a
Liters of Solution
0.067 L
0.050 L
0.050 L
pH (use universal
solution)
0.82
11.2
7.1
Molarity (based on
pH)
0.15 M
5.85 x 10-12 M
7.94 x 10-8 M
Color
Red
Blue
Purple
Yarn
(please attach!)
Part C: Post-Lab Questions
Please answer on a separate sheet of paper using complete sentences. Be sure to attach the pre- and postlab questions to your lab sheet.
1. If you add an acid to your plant pigment, what color will it turn? What other plants do you expect
to see the same color change in? Why?
If you are adding an acid such as vinegar or hydrochloric acid to red cabbage juice it will turn red. Plants
that will have similar color change are beets, eggplant skins, and any other plant with anthocyanin
pigment in it.
2. If you add a base to plant pigment, what color will it turn? What other plants do you expect to see
the same color change in? Why?
Name:
Period/Block:
Date
If you are adding a base such as baking soda or sodium hydroxide to red cabbage juice it will turn a deep
blue. Plants that will have similar color change are beets, eggplant skins, and any other plant with
anthocyanin pigment in it.
3. What color should your plant pigment turn if you combine the same amount of an acidic solution
of a pH of 3 with a base with a pH of 10? Justify your answer.
The combined solution would be 7 (the difference of pH 10 – pH of 3). If a neutral solution with a pH of 7
is added, we would expect to not see any color change because there would not be any excess acid or base
added to the red cabbage juice.
Part D: Molarity and pH Practice Problems
Please answer the following questions on a separate sheet of paper being sure to show all work and all units.
Please be especially careful in keeping your signs (positive/negative) correct when working with scientific
notation.
1. Please fill in the following table, showing all of your work on a separate sheet of paper.
pH
1
2
3
4
5
6
7
Concentration
of Acid
1.0 x 10-1
1.0 x 10-2
1.0 x 10-3
1.0 x 10-4
1.0 x 10-5
1.0 x 10-6
1.0 x 10-7
Concentration
1.0 x 10-13 1.0 x 10-12 1.0 x 10-11 1.0 x 10-10
of Base
1.0 x 10-9
1.0 x 10-8
1.0 x 10-7
pH
8
9
10
11
12
13
14
Concentration
of Acid
1.0 x 10-8
1.0 x 10-9
1.0 x 10-10
1.0 x 10-11
1.0 x 10-12
1.0 x 10-13
1.0 x 10-14
Concentration
of Base
1.0 x 10-6
1.0 x 10-5
1.0 x 10-4
1.0 x 10-3
1.0 x 10-2
1.0 x 10-1
1.0 x 100
1. What is the pH of a 0.0045 M solution of hydrochloric acid (HCl)?
pH = - log [0.0045 M]
pH = 2.34
2. What is the pH of a 0.0045 M solution of sodium hydroxide (NaOH)?
Name:
Period/Block:
Date
pOH = - log [0.0045 M]
pOH = 2.34
pH + pOH = 14
pH + 2.34 = 14
pH = 11.66
3. What is the molarity of a solution with a pH of 6.4?
6.4 = - log [H3O+]
[H3O+] = 10-6.4
[H3O+] = 3.98 x 10-7 M