4.3: Lab Report
Record the color of each tube below. Note: record both initial and final colors at pH 12 and 14, since the pigments are not stable at these pH values. Save these tubes for the entire lab period .
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pH: |
2 |
4 |
6 |
7 |
8 |
10 |
12 |
14 |
|---|---|---|---|---|---|---|---|---|
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Color: |
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Record your pH values below:
|
Solution |
pH (pH paper) |
pH (cabbage extract) |
[H + ] (use pH from pH paper to calculate) |
|---|---|---|---|
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Unknown solution A |
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Unknown solution B |
- Do the results obtained for solutions A and B using the pH paper match those of the cabbage extract method? Yes / No Explain: __________________________________________________________________________________________________________________________
- Use the pH from the pH paper to calculate [H + ]. Record your value in the table.
- Which solution is more acidic? Unknown solution A / Unknown solution B
Exercise B: Determining the pH of Some Common Solutions
Many beverages differ in their pH levels due to CO 2 content (if carbonated) or differences in their levels of organic acids.
Record your values below:
|
Beverage |
pH |
List beverages in order of increasing [H + ] |
|---|---|---|
|
Apple juice |
Lowest: |
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Coffee (black) |
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Sprite |
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White wine |
Highest: |
Record your pH values below:
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Medication |
pH |
|---|---|
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Aspirin |
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Alka-Seltzer / Sodium bicarbonate (NaHCO 3 ) |
- Health care providers often recommend that aspirin be taken with a large glass of milk or water. Based on your results above, why might this be important? _________________________________________
- Would apple juice be a good replacement for water or milk while taking aspirin? Yes / No Explain: __________ ______________________________________________________________________________
- The normal pH of the stomach is around 2-3. How might the Alka-Seltzer affect the stomach and/or digestion? _______________________________________________ What might happen if someone uses too much Alka-Seltzer? _____________________ ______________________________________________________________________________
Based on your experiences with the cleaning solutions below, predict their pH value. Then, use the cabbage indicator method (2 mL of assigned cleaning solution + 1 mL cabbage extract) to determine the actual pH values of the cleaning solutions:
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Cleaning solution |
Predicted pH |
Actual pH |
|---|---|---|
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Drano |
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Ivory Liquid |
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Cascade |
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Tide |
Transfer the estimated pH values from Exercise C to the table below. Then, measure the pH and record your values below:
|
Solution (20 mL) |
Estimated pH |
Measured pH |
[H + ] |
[OH - ] |
|---|---|---|---|---|
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Apple juice |
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Sprite |
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Maalox |
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Tide |
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Ivory Liquid |
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How that we have a more accurate measure of pH, we can calculate [H + ] or [OH - ] with our calculators. Since pH is expressed as a negative logarithm of [H + ], you need to determine the antilogarithm of the pH expressed as a negative number. Fill in your calculations above.
More practice:
|
Solution |
[H + ] |
pH |
|
Solution |
pH |
[H + ] |
|---|---|---|---|---|---|---|
|
Urine |
5.73x10 -5 M |
Lemon juice |
2.7 |
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Pancreatic juice |
7.98x10 -8 M |
Milk |
6.5 |
8. If the pH of a solution is 6, what is its OH - concentration? First, find the antilog of -6. This will give you the H+ concentration of the solution. Then, divide 1x10 -14 by [H + ] to get [OH - ]. Calculate this value: _______________
- If a solution has an OH - concentration of 1x10 -4 M, what is its pH? ___________________
- If a solution has an [H + ] = 1 x 10 -6 M, what is its [OH - ]? _____________________________
Record the initial color, initial pH, final color, and final pH for each solution below:
|
Unknown solution |
Initial color |
Initial pH |
Solution added |
Final color |
Final pH |
|---|---|---|---|---|---|
|
C + Congo red |
0.1 N HCl |
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C + Phenolphthalein |
0.1 N NaOH |
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D + Congo red |
0.1 N HCl |
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D + Phenolphthalein |
0.1 N NaOH |
- Which unknown solution contains buffers? C or D How could you tell? _____________________ ______________________________________________________________________________
- Which indicator would be best to use to determine the presence of an acid? _______________ What color would it appear at pH 2? ___________ pH 7? _____________ pH 9? _____________
- Which indicator would be best to use to determine the presence of base? _______________ What color would it appear at pH 2? ___________ pH 7? _____________ pH 9? _____________