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Finding Amount of CO2, trouble with my Alka-Seltzer, Water lab.

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Revo31:
I am having trouble with my Alka-Seltzer, Water lab.

The purpose of the lab is to figure out how much CO2 is produced when an amount of Alka-Seltzer is mixed with an amount of water. The only equation we have is:

Alka-Seltzer + H2O ---> CO2 + Products

I have tried every thing I could think of. I measured out 30mL of water, and 1g of Alka-Seltzer. The water was 28°C and the current atm of where I live = .832 atm

The Experiment: I filled a bucket with water (same temperature), placed a plastic bag (with the Alka-Seltzer in it) over the graduated cylinder full of water. I immediately placed the system (air tight cylinder with water and Alka-Seltzer mixing) under water so that the liquid products stayed about the same height as the water in the bucket. When I looked at the amount of liquid product left, it stayed at 30 mL (still with gas in the container). At this point, I am not sure where to go as I do not have a balanced equation (or the reactants in Alka-Seltzer) that I could solve using Stoichiometry. I have completed a similar task where I filled a plastic bag with approximately 10 mL of water and dropped .5g of Alka-Seltzer in and sealed the bag. I lost 1 mL of water, when poured back into the graduated cylinder, but I assume that was the remaining liquid in the bag.

I am not sure where to go from here, or if I am even doing the experiment properly.  If any one could let me know how to use my data (if I even have the right data), or maybe tell me where I am going wrong I would appreciate it.  Unfortunately I don't have the full equation for the reaction, I have looked around on the internet and still can't find it, all I know is Alka-Seltzer is made with aspirin, sodium bicarbonate and citric acid.  Thanks for the help.

Revo31:
I came across an equation that I believe is the reaction of Alka-Seltzer and Water:

3HCO3 (-1 charge)(aq) + H3C6H5O7 (aq) ----> 3CO2 (g) + 3H2O + C6H5O7 (-3 charge)(aq)

Unfortunately, I am not sure how to do the stoichiometry on this equation as the Alka-Seltzer and water are not seperate.  If anyone could help me with where my numbers go or what equations I need to use, I would appreciate it.  Thanks.

Donaldson Tan:
Alka-Seltzer is a mixture. It does not react with water. Water facilitates the reaction between 2 components of Alka-Seltzer. There is critic acid and sodium carbonate present inside Alka-Seltzer. Once you add water, both the acid the bicarbonate dissolves and become "contact" with each other. The alka-seltzer fizz is thus described by:

--- Quote from: Revo31 on February 11, 2006, 04:16:41 PM ---3HCO3 (-1 charge)(aq) + H3C6H5O7 (aq) ----> 3CO2 (g) + 3H2O + C6H5O7 (-3 charge)(aq)
--- End quote ---
The underlined substance is critic acid. The net ionic reaction is given by:
H+ + HCO3- => H2O + CO2

Revo31:
Thank you for the help.  I didn't realize that water was not a part of the reactant list.  I believe I got the correct answers now.  Thanks, I appreciate it.  ;D

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