Measuring CO2

[connie08]

I'm growing algae for my experiment and I want to measure how much CO2 is consumed by my algae. I'm growing it in bottles. Someone recommended that I could keep my algae in a capped bottle and trap the CO2 with KOH (potassium hydroxide) as KHCO3 (potassium bicarbonate, a solid). And then use a wet cotton ball or paper tissue with KOH, weigh it, then stopper up the test tube with it. When its done, take it out and weigh it again and use the difference in weight as the weight of the CO2 consumed by my algae. Would that actually work? Or would that kill the algae because it won't be aerated??

Another way I found is by using CO2 gas sensors but they are really expensive. My high school doesn't have one that I could use and I can't borrow it from any near by college labs either. But I found this CO2 gas sensor which is really cheap at http://www.futurlec.com/Gas_Sensors.shtml but I don't know if it is the right one because it looks different from the other ones that I've seen. If it is, then I would just buy this one.

I also found some gas sampling tubes which were cheaper but that would mean that I have to build a pump and I don't have enough time for that.

So is there any other way to measure CO2 easily? Please respond ASAP. Thank you!

[MelissaB]

Connie,

I am so sorry that no one has answered your question yet! The CO2 sensor you found does look like it would work. However, I have never used it, and I am a little suspicious given the price compared to the prices of other CO2 sensors. If I were you, though, I would definitely try it, because it might be a lot better than the KOH method (which you should go ahead and use if the CO2 sensor turns out not to work).

If you do use the KOH method, I suggest having lots of air in your bottles--so maybe only fill the bottles half-full of water/algae. With any luck, they will not die off due to low oxygen content in the time you will be studying them. Unfortunately, I do not work with algae and am not a chemist, so I am honestly not sure whether this approach will work and/or whether capping the bottles will kill off your algae in a week.

[donnahardy2]

Hi Connie,

Melissa has given you some good advice on your plant growth project. Enclosing the containers and adsorbing the CO2 with KOH would effectively remove all of the carbon dioxide from your samples and would limit the amount of oxygen in the system, and I’m not sure you would want to do this.

The technical data sheet for carbon dioxide sensor you have found is based on the electrical current produced by the reaction of lithium with carbon dioxide to from lithium ions and electrons. However, it doesn’t appear that the sensor reports results quantitatively; it is designed just to produce a current in response to the presence of carbon dioxide. And its sensitivity is 350 ppm carbon dioxide, which would be above the concentration of carbon dioxide you would expect in your samples. It is not clear from the technical data sheet, but I wonder if you could connect the sensor to a multimeter to measure the impedance to quantitate the results. You would need to have samples with known concentrations of carbon dioxide to establish a calibration curve.

Why don’t you contact the company and ask if they have any details about how to record the results so you can obtain quantitative results? Also, ask how much lithium is in the sensor so you can get an idea of how long the sensor will last. Most important, ask if the output could be adapted to measure carbon dioxide with greater sensitivity so it would be useful for your samples. Since this sensor is low cost, it might be ideal for use for a science project, but don’t order it until you can verify that it will be suitable for your samples.

What are your doing in your project? What is your hypothesis and your independent variable? Were you planning to measure plant mass as well as carbon dioxide? Perhaps there is another way to approaching your topic. Perhaps you could use literature sources that show the quantitative effect of carbon dioxide on plant growth. Have you found any information on this subject in your background reading?


Donna Hardy

[connie08]

Thank you for the quick replies.

I've just been notified that a teacher at my school can lend me an oxygen probe. Is there a way to calculate the amount of CO2 using the amount of oxygen?

And when I do my experiment, I'm growing the algae in bottles that will be capped for 5 days. I was going to measure the amount of CO2 (or O2) on the first day and then again after the 5 day period. Would this work or would it kill off my algae due to the lack of oxygen? I based my experiment off someone elses experiment and they let it grow for a week in a capped bottle and their algae didn't die. But they would shake their bottles. I don't really understand why they did that though.

Also, I'm varying the pH levels in each bottle. I was going to use crushed coral to change the pH levels but would it be kept at a constant pH level for 5 days?

Sorry for all the questions but I as I do my experiment, I keep on running into more problems.

[donnahardy2]

Hi,

Measuring the amount of oxygen is good and it will be helpful in this experiment, but measuring oxygen will not tell what the level of carbon dioxide is. However, you can still obtain lots of information with your available resources. I recommend recording the number of hours of sunlight, the temperature during each day of your experiment. You can measure the carbon dioxide at time 0 and at the end of day 5 using the KOH method, and you can measure the pH at the beginning and end of the experiment.

What type of algae are you using, and are you planning to measure the quantity of algae at the beginning and end of the experiment?

However, now you should relax. You have planned a controlled experiment and you independent variable is the pH at the beginning of the experiment. You can’t control what will happen after to seal the containers, but you should understand what has happened at the end of the experiment.

Here’s what could happen in the enclosed containers:

When exposed to sunlight, the algae will use carbon dioxide and water to produce sugar and oxygen :

6CO2 + 6H2O + Energy  C6H12O6 + 6O2

http://faculty.clintoncc.suny.edu/facul ... otosyn.htm

When exposed to sunlight and when it is dark the algae will use the glucose and oxygen to produce carbon dioxide and energy. Here is the equation for this process, called respiration:

glucose + oxygen = water + carbon dioxide + ENERGY

If the oxygen disappears from the system, then the plants might still produce energy by anaerobic respiration and they will use glucose to produce carbon dioxide and ethanol.

glucose = carbon dioxide + ethanol (alcohol) + ENERGY
C6H12O6 = 2CO2 + 2C2H5OH + ENERGY


If excess carbon dioxide is produced during the 5 days, some of it will dissolve in the water producing carbonic acid.

http://scifun.chem.wisc.edu/chemweek/pd ... ioxide.pdf


C6H12O6 + 6O2 = 6H2O + 6CO2 + ENERGY

If the pH is decreased, more of the calcium carbonate from the crushed coral will dissolve. However, calcium carbonate has limited solubility in water, but this does vary, depending on the pH. Look at the equilibrium equations in this Wikipedia site to help you better understand this:

http://en.wikipedia.org/wiki/Calcium_carbonate


You cannot control any of the parameters after you start the experiment; all of your results (pH, oxygen levels, etc) are your dependent variables.

Let me know if you have any other questions.


Donna Hardy

[donnahardy2]

Hi,

I forgot to answer the question about shaking the containers. This will help aerate the water sample and mix the available oxygen into the water. If you don't shake the containers, conditions at the bottom of the containers could become anaerobic quickly if the rate of respiration exceeds the rate of photosynthesis. You can either shake the containers or not, but this is one of your controlled parameters so you should treat each container exactly the same way.

Donna Hardy

[connie08]

Thank you! That clears things up.

I'm using coccolithophorid algae because they take in carbon dioxide and do not release the carbon dioxide after they have died. Instead, they trap it away in calcified plates known as coccoliths.

When I use the KOH method, does it give me the amount of CO2 that wasn't absorbed? Because I want to find how much CO2 was absorbed by my algae.

[donnahardy2]

Hi,

One way you could do this is by weighing your samples after ashing them. You would need a control sample that represents day 0, and then ash all samples at the end of the experiment. Ashing involves heating samples at a high enough temperature to vaporize all organic molecules, leaving the ash, which in the case of coccolithophorids would be the calcium carbonate.

Ashing is usually done in ashing furnaces, also called muffle ovens. You should be able to substitute an oven that can do a high temperature cleaning cycle or a pottery kiln. You would need ceramic crucibles to hold the samples.

http://www.carbolite.com/products.asp?id=3&doc=4

Let me know if you have more questions.

Donna Hardy

[connie08]

Okay. I'll do that.

Also, I have to vary the temperatures (15, 20 and 25 Celsius). I was going to put it under lights and just vary the distance they are from the lights to change the temperature. Would this work?

And I'm going to grow my algae in a Marine Algae Culture Medium (http://wardsci.com/product.asp?pn=IG0011450) and then add the crushed coral to vary pH. The medium just gives my algae nutrients that it needs to grow right?

[donnahardy2]

Hi,

How many samples are you planning to test? With two independent variables (3 temperatures and 3 pH levels) you will need 9 samples. One independent variable is plenty for a science fair project, and you could run samples in duplicate (6 samples) to test the reproducibility of your experiment. If you vary the distance of the lamp to control the temperature, this will also vary the light intensity provided to each sample, this will add another variable, which you don't want to do. If you do want to test temperature, then it would be better to provide the same amount of light to each container and find a different way to control the heat. Or, just eliminate temperature and run duplicate samples for the different pH levels. It's really good you are thinking about all of this before you set up your experiment.

I like the marine algae medium because it is provided sterile and this will eliminate a possible unwanted variable due to contamination. However, it's so expensive! Do you have access to a few chemicals at school? You could make the medium yourself, and sterilize it by boiling or in an autoclave or pressure cooker. Here's a recipe for marine algae medium:

http://www.thelabrat.com/protocols/Blue ... roth.shtml

Or, you could buy Instant Ocean from a local pet supply store and compare ingredients to see if you need to add anything. Or, if you live close the ocean, you could collect your water for free, and filter it and sterilize it. The composition of your water is one of your controlled parameters, so you want to use the same water for all samples.

Donna Hardy

[connie08]

Hi,

The Science Fair Manager recommended that I test temperature as well so that I would have a stronger project. But now I don't know how I could control it so I might only test pH. Do you think that my project will be weaker if I don't test temperature?

And you're right, the medium is expensive so I'll just use the Instant Ocean and mix it with distilled water.

Thank you for all the help!

[donnahardy2]

Hi,

The science manager was trying to provide you with a helpful suggestion, and was correct; adding an additional independent variable could improve a project. And, temperature is an interesting parameter to study in this group of algae. Here is a paper, which, unfortunately, I can only access the abstract for. Please notice that temperature was the only topic studied in the paper. The authors found that these organisms grow at 10 to 25 degrees Centigrade (E. huxleyi) and Gephyrocapsa oceanica grew only between 20 to 25 degrees C. The authors report that cells were larger and produced more coccoliths at a lower temperature. Also of interest for your project is that the lag time was for the cultures 5 days.

http://www.springerlink.com/content/m6885408k4n77428/

So, unless you have a good way to controlling the temperature in the optimum temperature range for the species that you are studying, I think you should just do pH. But you should measure the temperature to make sure it is within the optimum range.

Here’s another paper on optimum temperature:

http://lgmacweb.env.uea.ac.uk/green_oce ... O_2008.pdf

Light and phosphate concentration is also important for coccolith formation, so make sure you provide optimum conditions for these parameters:

https://circle.ubc.ca/handle/2429/3130

Another paper on optimum conditions for coccolith formation:

http://www.osti.gov/bridge/purl.cover.j ... Pk/native/

One of the articles above used cultures that were stirred continuously, so apparently this does help in the growth of the organisms and would mimic conditions in the ocean. So I would recommend that you mix up your cultures every day.

You can reduce the lag time by starting with a rapidly growing culture under optimum conditions.

Donna Hardy

[connie08]

Thank you for all your help.

I think I'll just test pH since I don't have a good way to control the temperature. What would my control be in my experiment? Would it be the sample with no crushed coral added?

[donnahardy2]

Hi,

Yes your control would be a sample grown at the normal pH of ocean water, with no coral added; you should include one control that you seal, so you see if there any effect for sealing the containers and one that is left open to ambient air.

Donna Hardy

[att159]

You could ask around at a nearby university if they have an Co2 probes which you could borrow.
Or you could contact a company asking for a donation of a co2 probe.

Good luck!

[connie08]

Thanks for all the help!

[connie08]

Hi,

Sorry but I have another question. To make my project stronger, I've been thinking about maybe testing two different temperatures. I would put some in a cooler and then I would leave some in room temperature. Should I do this?

[donnahardy2]

Hi Connie,

I would recommend this only if it makes sense from a scientific point of view, not just to increase the complexity of the experiment. What species are you working with? If you are working with a species that only grows between 20 and 25 degrees C, then I would not recommend it because you know from the literature that the organism won't grow in the cold. If you are working with one that grows from 5-25 degrees C, then it might make sense, based on the reference that reported a larger cell size and more calcium deposited with cultures grown at lower temperatures. However, since a lower temperature will slow the growth rate, you would need to increase the time of the experiment.

If you want to do more on this project, how about counting the algae and measuring the average cell size at the beginning and end of the experiment? This would add more data and make your project stronger. Do you have access to a microscope?

Donna Hardy

[connie08]

Yes, I do have access to a microscope. I'll measure the average cell size instead of testing temperature. Thank you for your advice!

[connie08]

Hi,

I've never worked with Instant Ocean before so I didn't know that it didn't contain any phosphate or nitrate nutrients. I was going to add it to distilled water, but then my algae wouldn't have any nutrients. So could I just use the water that was originally in the plastic water bottles instead of distilled water so my algae will have some nutrients? Or should I go out and buy some nutrients? If I need to buy some, what would you recommend to buy?

Thank you.

[MelissaB]

Hi,

You will need to get nutrients--water from water bottles probably won't have enough for your algae to grow. I would suggest going to a plant shop and asking for hydroponic fertilizer--this is fertilizer designed for growing plants in water. You could also explain what you are doing and just ask if they have suggestions for fertilizer and how much to use, etc.

Good luck!

[donnahardy2]

Hi Connie,

Melissa has given you excellent advice. Be sure that you don't exceed the recommended amount of the fertilizer since this would be toxic to the algae.

Donna Hardy

[deleted-71684]

A O2 or CO2 probe may be the easiest solution to your experiment, but I wanted to suggest another possible idea for you to think about. You could try using the Winkler Test for dissolved oxygen. Its a pretty old test, but it works well and is fairly simple (and cheap) to do. Furthermore, I think science fair judges would love to see that you have performed this test because it tests your knowledge of solutions chemistry, titrations, and it also provides you with a lot of data which you will have to manipulate and interpret. I have attached a link that explains how the test works:
http://serc.carleton.edu/microbelife/re ... xygen.html

Best of luck!