This endothermic reaction of Alka Seltzer is a state change. What state change do you think it is?
Approximately 3 weeks before finals I came down with an illness, I have not been sick in years so this was quite a surprise and bad timing!! In Chemistry I have really struggled. It is a hard subject to learn! As I was sick in bed for about three days I was thinking of final projects and realized the very things right in front of me where creating intense chemical reactions!
C16H17NaO14
Active Ingredients: in each tablet: Aspirin - 325
mg (NSAID* Pain Reliever / Fever Reducer), Chlorpheniramine Maleate - 2 mg
(Antihistamine), Phenylephrine Bitartrate - 7.8 mg (Nasal Decongestant)
Inactive Ingredients: Acesulfame Potassium, Anhydrous Citric Acid,
Aspartame, Calcium Silicate, Dimethylpolysiloxane, Docusate Sodium, FD&C
Red #40, FD&C Yellow #6, Flavors, Mannitol, Povidone, Sodium Benzoate,
Sodium Bicarbonate
To take the tablets, you should fully dissolve them in a glass of water, where they undergo a chemical reaction that produces lots of carbon dioxide (CO2) bubbles. As the tablets dissolve, the sodium bicarbonate splits apart to form bicarbonate (HCO3-). This reacts with hydrogen (H+) from citric acid, another ingredient in the tablets. This chemical reaction forms water and carbon dioxide gas.
I also discovered that the temperature of the water makes a difference in how fast the tablet dissolves. In cold water, which tastes much better, the tablet takes longer to dissolve, the bubbles are larger and spread further apart. In hot water however the tablet dissolves almost instantly, the bubbles are small and seem to be many more. Obviously as with boiling water for example the higher the temp the faster the molecules move. In both temps the bicarbonate contacts hydrogen to create carbon dioxide but in the higher temps this process is faster and more likely.
In cold water the tablet took approximately 150 seconds to completely dissolve and in hot water it was about 38 seconds!
As the tablets dissolve the sodium bicarbonate dissolves to form bicarbonate, this reacts with hydrogen in the tablet (actually in the anhydrous citric acid) another ingredient in the tablets. This forms the carbon dioxide gas and also water.
Surprisingly the active ingredients in Alka Seltzer are not where your chemical reaction comes in. These are the more complex compounds in Alka Seltzer, and what makes you feel better!
Alka Seltzer is a mix of different compounds, so it is a mix of the two. The “inactive” ingredients are where you find the molecules that cause the state change. The two molecules that cause the chemical reaction act independently sodium bicarbonate, and anhydrous citric acid.
Sodium bicarbonate is a mixture of both. It is NaHCO3. The HCO3 is covalently bound together, where the C contains a double bond to O, a single bond to OH, and a single bond to the last O. This last single-bonded O has a negative charge, which forms an ionic bond to Na.
As the tablet dissolves in water, an acid base reaction between the citric acid and sodium bicarbonate takes place with the evolution of carbon dioxide gas.
Here is the Lewis dot structure for sodium bicarbonate
Reflection~ There was definitely nothing easy about this class. Chemistry is fascinating and causes you to think about the reactions surrounding you every single day. Taking this class forced me to think more deeply about the compounds, elements and molecules that make up the universe around me. It also taught me that I need to be able to pull apart story problems in math better! Chemistry is all about math and being able to measure the wights of elements and molecules in the universe. I wish I would have taken this class in the classroom, all in all though I did gain perspective and learned a great deal about chemical equations, chemical reactions, the types of bonds molecules make and reactants, solutions and solutes.
For me the most fascinating parts of chemistry are the state changes. This is why I choose to do my project on the chemical changes in Alka Seltzer! There are chemical changes surrounding you everyday. See what you can discover!
