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Name: Ella Status: student Grade: 6-8 Location: UT Country: USA Date: Spring 2013

Question:
For my science fair experiment, I am dissolving Vitamin C tablets in solutions of different pH, and for one of those substances I uses baking soda water. This was by far the fastest liquid to dissolve the tablet, it only took about 30 minutes. When I put the tablet into the mixture, it started fizzing and looked like it had a little slip-stream around it made of bubbles/Vitamin C bits. I was wondering what chemical reaction was happening here. Also, no other bases did this, only the baking soda.

Replies:
Any solid acid will cause baking soda to fizz. Baking soda, NaHCO3, releases carbon dioxide gas CO2 in the presence of the hydrogen ion H from any acid HA:

NaHCO3 + HA à NaA + H2O + CO2

Richard E. Barrans Jr., Ph.D., M.Ed. Department of Physics and Astronomy


Ella,

Vitamin C is an acid, although a weak one. Baking soda is a base. I suspect that you are producing carbon dioxide gas.

I haven’t balanced the equation but the reactants and products might look like this: C8H8O6 (vitamin C – reduced form) + NaHCO3 (baking soda) à Na+ (sodium ion) + H2O (water) + CO2 (gas) + C8H8O6 (vitamin C – oxidized form)

Ray Tedder, NBCT


The reaction of ascorbic acid with baking soda releases carbon dioxide. The convection induced by the bubbles would help dissolve the vitamin C faster. Try stirring the solution to promote dissolution with bases that do not release carbon dioxide.

Sri R Narayan


Ella,

You may need to make a distinction between a solid that dissolves into a liquid (essentially remaining the same compound but now separated out and mixed with the liquid) versus a solid that reacts with the liquid and becomes some other compound which then dissolves into the liquid.

In the first case, the substance did not change its molecular structure. The atoms are still bonded in the same way and the molecules are still intact. What happened was that the solid - a compact bunch of molecules, got mixed into the liquid so that the compact bunch of molecules got separated into individual molecules and are now mixed in thoroughly with the molecules of the liquid.

In the second case, the individual molecules of the solid got broken down into smaller sections. Some liquid molecules also got broken down into smaller sections. Then, the smaller sections that came from the solid molecules combined with the smaller sections that came from the liquid molecules and made new molecules.

The reason the tablet "dissolved" into basic solutions faster is because Vitamin C is an acid and this particular reaction of an acid and a base is a fast one. So the Vitamin C was not actually dissolving into the basic solution, it was reacting with the base in the solution.

The reason you observed bubbles form with baking soda as the base is because the particular reaction of the Vitamin C and baking soda produces a gaseous product. The gas was carbon dioxide and it as it was produced, it formed bubbles.

Greg (Roberto Gregorius) Canisius College


Undoubtedly the chemical reaction that takes place is between Vitamin C, (ascorbic acid), {also identified by its CAS number [50-81-7]} and sodium hydrogen carbonate {NaHCO3 [144-55-8]}. I am also intentionally using the CAS numbers so that they become more familiar. Although, not so familiar, they are important because they are an important "shorthand" for identifying specific chemical compounds. The "fizz" is the evolution of carbon dioxide gas [124-38-9].

The "speed" of the reaction is a consequence of how fast the CO2 gas escapes from the surface of the sodium hydrogen carbonate. This is very dependent upon particle size, the other variables that are difficult to quantify. My warning to students is: "Always be alert to questions about RATE. Rates are always much more difficult to measure, even though the concept sounds "simple"". Rates are not easy to quantify.

Vince Calder



Hi Ella,

Thanks for the question. The Vitamin C tablet dissolves in water and release acid (H+ ions). These H+ ions reaction with baking soda to produce bubble of carbon dioxide which is the fizzing you observed. The chemical reaction is:

H+ + HCO3- ---> CO2 + H2O

The baking soda is sodium bicarbonate, HCO3- and carbon dioxide is CO2 which is a gas.

I hope this helps. Please let me know if you have more questions. Thanks Jeff Grell


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