Acid Rain* Lab

 

Theory:
Water is able to absorb a large variety of chemicals, leading us to call it the "universal solvent". In this lab we will be looking at how water absorbs CO2 gas. We will be observing the pH level of the water sample as CO2 is absorbed, forming carbonic acid and lowering the pH level. This lab will point the way to other gases being absorbed and similarly being converted to acidic compounds.

Purpose:

Study the absorption of CO2 by water.

Equipment:

pH Sensor, LabPro, Macintosh or PC Computer, 50-ml grad cylinder, water, straw

Procedure:

  1. Plug the pH Sensor into CH1 of your LabPro. Connect the LabPro to your computer then launch Logger Pro software. When the software gets launched successfully, it should have set up a graph of pH vs. time.
  2. Press the icon with the stopwatch next to the LabPro icon. Click on the "Sampling" tab. Set the time for data collection to 4 minutes. A rate of 1 sample per second is good. Click [Okay] to set this data rate.
  3. Put 10 ml of distilled water at room temperature in the graduated cylinder. Put a similar amount of water in a test tube and place in an ice water bath. Prepare another test tube but place it in a hot water bath.
  4. Insert the pH Sensor in the room temperature water. Also insert the straw so that it is fully below the water line. Begin collecting pH readings. After about 30 seconds, begin blowing gently through the straw, bubbling into the water. Note changes in the pH readings. Keep blowing gently for one or two minutes. Then let thing settle out for the last minute of data collection.
  5. Once data collection is completed, press the Autoscale icon (the dotted rectangle with the "A"). This scales the graph so your data fills it completely. Go to Analysis questions 1 and 2. Then return to the next step of this procedure.

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  6. Go to Data, then "Store Latest Run…". This will leave the previous data on the graph and allow a second run to be plotted over the top for easy comparison.
  7. Rinse the bulb of your pH Sensor with distilled water, then repeat steps 4 & 5 for the water that was stored in the ice water bath. Complete Analysis question 3. Then go to the next step of this procedure.

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  8. Store that latest run, too. Rinse the bulb of your pH Sensor with distilled water, then repeat steps 4 & 5 for the water that was stored in the hot water bath. Complete Analysis question 4.

 Analysis:

  1. What was the pH reading of your distilled water? Does this reading indicate the water is acidic, basic or neutral?
  2. Describe the graph generated as you blew air through the water. Note that the CO2 in your breath was combining with water molecules to form carbonic acid, H2CO3. Does the direction of the graph indicate that carbonic acid is being formed?
  3. How does the pH change of the cold water compare to the pH change for the room temperature water? If it was a larger change, what does that indicate about the amount of CO2 that was absorbed?
  4. How does the pH change of the hot water compare to the pH change for the room temperature water? If it was a larger change, what does that indicate about the amount of CO2 that was absorbed? Is hot water or cold water able to absorb more CO2, based on your experimental results?

 Extension:

Compare the rate at which the pH changes if you have been resting recently and if you have been exercising. For example, run in place, run around the building or do some jumping jacks immediately before blowing into the straw. What does this say about the amount of CO2 that you have in your breath?

 

*This isn’t really an Acid Rain Lab. Due to absorbing CO2 and forming carbonic acid, airborne water is slightly acidic. In a similar manner, SOx and NOx are both absorbed forming acidic compounds that contribute to the problem we call acid rain. The more SOx and NOx in the air as a result of burning fuels, the more acid rain we generate.

Compare this lab with #22 in the Chemistry with Vernier lab manual.

MS Word computer version - AcidRain.doc

pdf computer version - AcidRain.pdf

MS Word LabQuest version - AcidRainLQ.doc

pdf LabQuest version - AcidRainLQ.pdf

MS Word calculator version - AcidRainCalc.doc

MS Word calculator with Easy Data version - AcidRainEasy.doc

pdf calculator with Easy Data version - AcidRainEasy.pdf

MS Word computer with Logger Lite version - AcidRainGo.doc

pdf computer with Logger Lite version - AcidRainGo.pdf

MS Word Palm OS version - AcidRainPalm.doc

Click here to download an experiment file that can be installed on a LabQuest: acidrain.lqu

Click here for instructions on how to install this file on your LabQuest.

 

Clarence Bakken
January 2009