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.

pH vs. color of solution

pH:	2	4	6	7	8	10	12	14
Color:

Record your pH values below:

pH and [H+] of unknown solution A and B

Solution	pH (pH paper)	pH (cabbage extract)	[H^+] (use pH from pH paper to calculate)
Unknown solution A
Unknown solution B

6. Do the results obtained for solutions A and B using the pH paper match those of the cabbage extract method? Yes / No Explain: __________________________________________________________________________________________________________________________
7. Use the pH from the pH paper to calculate [H⁺]. Record your value in the table.
8. 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 CO₂ content (if carbonated) or differences in their levels of organic acids.

Record your values below:

pH and [H+] of household solutions

Beverage	pH	List beverages in order of increasing [H^+]
Apple juice		Lowest:
Coffee (black)
Sprite
White wine		Highest:

Record your pH values below:

pH of household medications

Medication	pH
Aspirin
Alka-Seltzer / Sodium bicarbonate (NaHCO3)

1. 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? _________________________________________
2. Would apple juice be a good replacement for water or milk while taking aspirin? Yes / No Explain: __________ ______________________________________________________________________________
3. 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:

predicted and actual pH of household solutions

Cleaning solution	Predicted pH	Actual pH
Drano
Ivory Liquid
Cascade
Tide

Transfer the estimated pH values from Exercise C to the table below. Then, measure the pH and record your values below:

pH, [H+], and [OH-] of household solutions

Solution (20 mL)	Estimated pH	Measured pH	[H^+]	[OH^-]
Apple juice
Sprite
Maalox
Tide
Ivory Liquid

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:

pH and [H+] of household solutions

Solution	[H^+]	pH		Solution	pH	[H^+]
Urine	5.73x10^-5M			Lemon juice	2.7
Pancreatic juice	7.98x10^-8M			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:

color and pH of unknown solutions C and D

Unknown solution	Initial color	Initial pH	Solution added	Final color	Final pH
C + Congo red			0.1 N HCl
C + Phenolphthalein			0.1 N NaOH
D + Congo red			0.1 N HCl
D + Phenolphthalein			0.1 N NaOH

10. Which unknown solution contains buffers? C or D How could you tell? _____________________ ______________________________________________________________________________
11. 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? _____________
12. 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? _____________