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Red Cabbage Indicator


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
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. 
·         In this activity:
·         If the indicator turns the solution red or pink, the solutions are acids.
·         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.   
Notes:
·         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
Household Product
Prediction à Acid, Base, Neutral
Initial color of product
Initial color of indicator
Final color of indicator 
Estimated pH Values
Acid
Base
Neutral
1.       HCl (hydrochloric acid)
 
 
 
 
 
 
 
 
2.       Water
 
 
 
 
 
 
 
 
3.        
 
 
 
 
 
 
 
 
4.        
 
 
 
 
 
 
 
 
5.        
 
 
 
 
 
 
 
 
6.        
 
 
 
 
 
 
 
 
7.        
 
 
 
 
 
 
 
 
8.        
 
 
 
 
 
 
 
 
9.        
 
 
 
 
 
 
 
 
10.    
 
 
 
 
 
 
 
 
11.    
 
 
 
 
 
 
 
 
12.    
 
 
 
 
 
 
 
 
13.    
 
 
 
 
 
 
 
 
14.   NaOH (Sodium Hydroxide) 
 
 
 
 
 
 
 
 
 
DATA (Color your drawings!) 
a.       This DATA table (25 pts)
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)
 
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) 
SESSION 2.
ANALYSIS Questions (pH post-lab questions) Answer the following questions completely. 
  1. The main idea of this lab was …
  2. It is important to learn about acids and bases because …   
  3. When you added vinegar to red cabbage indicator, the indicator changed color from _______________ to ___________.  
  4. Why and when does red cabbage juice changes from purple to other colors? 
  5. When you added vinegar to baking powder, you noticed that …    
  6. List the substances you tested from most acidic to most basic.
  7. The data shows that most foods are mostly __________ because …            
  8. Cleaning supplies are mostly __________ because... 
  9. 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 ____________________. 
  10. 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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