| MadSci Network: Chemistry |
Your question has several parts, so I will try to break them down individually.
The Carbon dioxide (CO2) produced by Sodium bicarb is the same CO2 that is dissolved in carbonated soft drink (CSD). However, there is a major difference between dissolved CO2 in CSD and CO2 produced by decarboxylation (release of CO2 from a reaction). The dissolved CO2 in CSD is at a much higher concentration. It is dissolved under pressure in really cold water. Basically many more dissolved bubbles.
The difference between Sodium bicarb and Alka seltzer is that Alka seltzer contains sodium bicarb, aspirin, citric acid, and sweetener. The acid must be present to produce the decarboxylation (release of CO2) reaction.
The last question is a little hazy for me. I think you want to know why aspirin dissolves faster in CSD than in Sodium bicarb or Alka seltzer. The answer revolves around the dissolved CO2 in CSD. Even though CO2 is a gas it will dissolve in the CSD. The dissolved CO2, as it is released from the CSD, agitates the aspirin to make it dissolve faster. This is the same principle used when dissolving any powder in water. It will dissolve faster if you shake the container. The CO2 is providing the "shake".
If you observe CO2 release from CSD in a glass you will notice that the bubbles are released in a line from bottom to top. The origin of the CO2 release is called a nucleation site. A nucleation site is a sharp surface that will allow the CO2 to coalesce (grow around and then eventually be released as a bubble). The nucleation site can be a small scratch on the glass or a tiny imperfection. Another source for the nucleation site can be a crystalline structure like aspirin. So the apsirin will attract the dissolved CO2 to provide even more direct agitation and therefore even faster dissolving action.
One last suggestion is to try the experiment with Sierra Mist. It just tastes better!!
Mad Scientist/Pepsi Scientist Dave
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