Try this: Colour-changing cabbage
We're going to make an indicator solution, which changes colour when
it is mixed with an acid or a base.
You will need
- Fresh red cabbage (which is purple); a sharp knife;a cutting board; hot tap water
- a strainer & a funnel
pH scale for red cabbage can be found: http://www.csun.edu/~aef21890/coursework/525/assignments/acids%2520%26%2520bases%2520demo-l...
Preparation of red cabbage indicator (done by the teacher the night before)
1. Cut ½ of a cabbage into small pieces.
2. Cook cabbage in 2 liters of water for about 15 minutes
3. Separate the bluish-purple liquid from the cabbage and let it cool
pH Determination of Household Products (student lab activity) – red cabbage (any food store has it), tools to cook red
cabbage for 15 minutes, red cabbage juice, red cabbage juice pH scale, pH
paper, sodium hydroxide, hydrochloric acid, pipettes or syringes, 50 mL or
smaller pastic cup or beaker for each substance being test, common house
products in liquid for (vinegar, lemon juice, 7-up, windex, ajax, soap, bleach,
baking soda, bleach, etc), and beaker for waste.
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In this activity:
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If the indicator turns the
solution red or pink, the solutions are acids.
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A purple solution indicates
that it is neutral, neither an acid nor a base.
·
If the indicator turns the
solution blue, green, or yellow, the solutions are bases.
pH Determination of Household Products
Lab #
1. Predict
the pH value of substances & estimate the pH value by using the red
cabbage juice indicator
2. Use the
indicator to identify acidic, basic, and neutral substances found in any
home
3. Classify
household items as acids and bases
4. Collect
and analyze data
5. Organize
and analyze results in tables and graphs
a.
Hypothesis/prediction: All items used to clean will be more
like (acids/bases) because _________
___________________________________________________ and items used as foods
will be more like (acids/bases) because __________________________________.
b.
The indicator being used is ______________________________.
c.
The independent variable is _____________ and the dependent variable is
_____________.
PROCEDURE
Estimating
pH values with red cabbage indicator – complete data table!
4. line up all substances to be tested on top of white paper
5. write each name in your data table à data table!
6. predict each substance as basic, neutral, or acidic à data table!
7. record the color of each substance to be tested - best to use color
pencils! à data table!
8. observe the red cabbage indicator, record its color à data table!
9. place a labeled beaker in front of each substance to be tested
10. add about 5-10mL of red cabbage indicator to all labeled beakers
11. to the corresponding cups with indicator, add drop by drop up to 5mL
of (1mL = 16 drops) the substance to be tested & record the color change
of the indicator à data table!
12. organize all cups from most acidic to most basic using as a guide the
pH scale for red cabbage juice
13. estimate the pH value of each substance by using the pH scale for red
cabbage juice à record in the data table!
14.
classify each
product as acid, base, or neutral à record in the data table!
15.
slowly pour 2 mL
of vinegar into 2 mL of baking powder and write your observations
16.
add 2 mL of milk
into each cup (A & B). Add 6 drops
of water to cup A. After each drop,
mix well & record any change.
Using vinegar, repeat the procedure with cup B and record any
changes.
CLEAN
UP! Pour all substances in the waste
beaker & rinse each used beaker.
Dry each cup & leave everything the way you found it. Remember
no traces of water on your working area or -25pts for each member of the
group.
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·
steps 4-14 can be done in one class
period, as wells as collecting the data in the following table
·
another class period is needed to
discuss the results and answer the following analysis question as well as
preparing their graphs – students may need to finish for homework
DATA
Table 1 pH of Common Household Products
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Household Product
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Prediction à
Acid, Base, Neutral
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Initial
color of product
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Initial
color of indicator
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Final
color of indicator
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Estimated pH Values
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Acid
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Base
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Neutral
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1. HCl (hydrochloric acid)
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2.
Water
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3.
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7.
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8.
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9.
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10.
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11.
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13.
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14. NaOH (Sodium Hydroxide)
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DATA (Color your drawings!)
a.
b.
Draw cups with indicator (5
pts)
c.
Draw household products being
tested (5 pts)
d.
Draw all cups after adding
the substances being tested with the indicator (5 pts)
e.
Graph your results from the
most acidic to the most basic (10 pts)
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pH Lab Report specifics -
due on _________ (100 pts)
1.
Introduction – write a paragraph
explaining the big concepts and who they are related to the lab (15 pts)
2.
Under the introduction write the following:
a. objectives (5
pts) b. hypothesis (5 pts) c. variables (5 pts)
3.
Data - items a-e in this order (50
pts)
4.
Analysis – questions 1-10 (10
pts)
5.
Conclusion (10 pts)
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SESSION 2.
ANALYSIS Questions (pH post-lab questions) Answer the following questions completely.
- The main idea of this lab was …
- It is important to learn about acids and bases because …
- When you added vinegar to red cabbage indicator, the indicator
changed color from _______________ to ___________.
- Why and when does red cabbage juice changes from purple to other
colors?
- When you added vinegar to baking powder, you noticed that …
- List the substances you tested from most acidic to most basic.
- The data shows that most foods are mostly __________ because …
- Cleaning supplies are mostly __________ because...
- In the investigation with test tubes A & B the problem being
investigated was … The dependent variable was ________________. The control was ______________. My conclusion in this exercise is
____________________.
- In living things, pH is maintained within a narrow range. Why is pH important in maintaining
homeostasis?
Conclusion starter
(write at
least 1 paragraph to explain how your results support or reject your
hypothesis, what you learned, and how you can improve your lab)
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