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					                                 Indicators Lab

SC7. Students will characterize the properties that describe solutions and the nature of acids and bases.
b. Compare, contrast, and evaluate the nature of acids and bases:
     Strong vs. weak acids/bases in terms of percent dissociation
     Hydronium ion & Hydroxide ion concentration
     Acid-Base neutralization
     pH


Essential Question: - How do we measure the strengths of acids & bases?


Purpose:
    To identify common substances as either an acid or base using chemical indicators
    To observe how a neutralization reaction may be detected by an indicator



Procedure:

Litmus Paper Test:
1) Place 5 drops of each unknown in a separate well on the chemplate.
2) Place a piece of blue litmus paper in each well and record the color change.
3) Place 5 drops of each unknown in a separate well (on the next row) of the chemplate.
4) Place a piece of red litmus paper in each well and record the color change.
5) Record results in table 1.
6) Throw away the litmus paper into the waste can.

pH Paper Test:
7) Place 5 drops of each unknown in a separate well (on the next row) of the chemplate.
8) Place a piece of hydrion “pH paper” in each well and record the color change.

Universal Indicator Test:
9) Place 5 drops of universal indicator in each well A-E, and record the color change.
10) Rinse & dry the chemplate.

Phenolphthalein Indicator Test:
11) Place 5 drops of phenolphthalein indicator in each well A-E, and record the color change.
12) Rinse & dry the chemplate.

Using Phenolphthalein to test Neutralization Reactions:
13. Using a clean dropper pipet add 10 drops of 1M HCl to a clean test tube and add one drop of
    phenolphthalein. Record the color in Table 3. Swirl the test tube to mix.

14. Dip the same pipet into the test tube and “spot a piece of pH paper, to test the pH of this solution. Record
    the pH in Table 3.

15. Using a clean dropper pipet place a few drops of 0.5 M NaOH to spot plate test well and add one drop of
    phenolphthalein. Record the color in Table 3.

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16. Dip the same pipet into the test tube and “spot a piece of pH paper, to test the pH of this solution. Record
    the pH in Table 3.

17. Using the NaOH dropper pipet add 0.5M NaOH drop by drop to the test tube containing the HCl until a
    color change occurs. Swirl the test tube to mix after the addition of each drop. Record the number of drops
    required, and record the new color.

18. Once the color change has occurred, use pH paper to determine the pH of the new mixture, by dipping a
    new pipet into the test tube and “spotting it on a piece of pH paper. Record the pH in Table 3.


Table 1. Data/Observations: Record the color change

 Solution        Blue Litmus         Red Litmus        Hydrion          Phenolphthalein             Universal
     A
     B
     C
     D
     E


Table 2. Results:

    Solution           Acid or Base             Approximate pH                Approximate Concentration
                                                                                   pH = -log [H+]
         A
         B
         C
         D
         E


Table 3. Neutralization Reaction
                                                     phenolphthalein
                Solution                                                                       pH
                                                         colour
                1.0M HCl
                   only
             0.5M NaOH only
After addition of NaOH to HCl causes
            colour change
Conclusion:



                                                         2
1. List all substances you tested and classify each as an acid or a base. Were any substances neutral (or nearly
   so)?

A=

B=

C=

D=

E=


2. Consider the items tested – what conclusion, if any, can you make concerning their pH?




3. Summarize the change in color of phenolphthalein; during the neutralization reaction – how can it be used to
    indicate
when the acid-base solution reaches the point where neutralization occurs?




4. How many drops of NaOH were required to neutralize the 10 drops of HCl?




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posted:11/30/2011
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