Mod 4 Lab 2 - Mod 4 Lab 2 PDF

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Mod 4 Lab 2...

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Participating in the Carbon Cycle From our knowledge of the carbon cycle, we have the general understanding that producers take in carbon dioxide to do photosynthesis and many organisms (plants and animals) release this gas as a waste product of cellular respiration. On the other hand, plants produce oxygen as a waste product during photosynthesis, and many organisms use oxygen gas to assist in the production of energetic ATP molecules during cellular respiration. Since carbon dioxide (CO2) and oxygen (O2) are colorless, odorless gases, we will not be able to determine which is present by looking or sniffing. We will instead use other means to determine whether each gas is present. One possible means involves the use of a candle – if a lit candle has CO2 “poured” onto its flame, it will be extinguished. If, on the other hand, if a glowing wood splint is exposed to O2, it will burst into flames. A chemical method of determining the presence of CO2 within a liquid is to use a pH indicator such as bromothymol blue (BTB). When a carbon dioxide molecule is combined with a molecule of water, the following reactions occur: CO2 + H2O → H2CO3 → H+ + HCO3The increase in hydrogen ions (H+) due to the addition of CO2 to water results in a pH change. The more carbon dioxide that is added to the water, the more acidic the solution becomes. The removal of hydrogen ions causes the solution to become more basic and shift the BTB indicator color. BTB is yellow below pH 6.0 and blue above pH 7.6.

Procedure: 1. Control. a. Add 100 ml of DI water to each of three containers. b. Add 10 drops of BTB to each container and stir. The water should be clear. c. Add drops of vinegar to one container stirring after each drop until a color change occurs. d. Add drops of ammonia to the second container stirring after each drop until a color change occurs. e. Add nothing to the third. f. Record the color of each solution in the table below. Additive Color

Vinegar Yellow

Nothing Clear

What does this tell you about the pH of vinegar and ammonia? The PH of vinegar is 7.6

Ammonia Blue

For the following parts of the lab, be sure your explanations are linked to cellular respiration (production of carbon dioxide) and photosynthesis (use of carbon dioxide) and pH change. 2. Human. a. Add 10 drops of BTB to 100ml of DI water. b. Add enough ammonia or vinegar to turn the water blue. (Determine which from your control. c. Take a deep breath and exhale (through a soda straw) into the container. Start a timer or look at a clock with a second hand when you begin. Continue taking breaths and exhaling into the solution until it turns yellow. Be careful to remove your mouth from the straw when taking supplemental breaths. What does the color change indicate about your breath? My breath is acidic How long did it take for the color to change? About 7-8 minutes d. Make another solution as you did in a and b. e. Once you have made this solution, precede this trial with a few moments of vigorous exercise. Jump up and down or jog briskly in place for 30 seconds to 1 minutes, then immediately begin blowing into the solution through a straw. Measure the time for the color change as you did before. How long did it take for the color to change after exercise? About 4-5 minutes Why did the time change? Because after exercising, my breathing rate was increased therefore increasing the rate at which carbon dioxide is expelled 3. Fish a. Fish were placed in two beakers with water containing BTB that was blue. What does the blue color indicate about the pH of the water? The PH of the water was >7.6 b. One beaker was kept in the light; one beaker was placed in the dark. c. Observe the results in the PowerPoint. What color was the water after the fish had been in the light? Yellow What color was the water after the fish had been in the dark? Yellow

Explain the color changes and why they were the same or different in light and dark. Because as the fish respirated, acid was introduced to the BTB, causing it to turn yellow. Regardless of the light, there was nothing to absorb the acid. 4. Yeast a. Yeast was placed in a tube with sugar and water containing BTB that was blue. b. One tube was kept in the light; one beaker was placed in the dark. c. Observe the results in the PowerPoint. What color was the water after the yeast had been in the light? Very light yellow, nearly clear What color was the water after the yeast had been in the dark? Darker yellow Explain the color changes and why they were the same or different in light and dark. The yeast in the light was able to respirate, allowing the CO2 to be absorbed, making it less acidic. The yeast in the dark was unable to respirate as well as the other, so the CO2 was not absorbed as efficiently, therefore the solution remained more acidic.

5. Algae Part 1 a. Algae was placed in a tube with water containing BTB that was blue. b. One tube was kept in the light; one beaker was placed in the dark. c. Observe the results in the PowerPoint.

What color was the water after the algae had been in the light? Very light blue What color was the water after the algae had been in the dark? Clear Explain the color changes and why they were the same or different in light and dark. The algae in the light was able to respirate, allowing the CO2 to be absorbed, making the solution more basic. The algae in the dark was unable to respirate at the same rate, therefore there was still an amount of CO2 in the solution, making it slightly more acidic and clear.

6. Algae Part 2 a. Algae was placed in a tube with water containing BTB that was yellow. What does the yellow color indicate about the pH of the water? The PH is...