Which chemistry experiment to do?

[NicholasAllen]

Hi,
I am doing a quantitative chemistry experiment for my next assessment and I have to choose between the following 3 experiments:

* Comparing commerical antacid tablets and commenting on their effectiveness
* Comparing commerical aspirin tablets and commenting on their effectiveness
* Comparing commercial fruit juices and commenting on their levels of ascorbic acid (maybe also using different environments they are stored in - i.e. warmer environments promotes oxidation?)

These topics all sound good to me, but which one should I choose? I want one which will give me a high mark (assuming I do well) and has lots to talk about - particularly with introductory research, chemistry, chemical concepts etc.

Any ideas would be greatly appreciated! Or thoughts to extend any of these investigations too! Thanks!

 

[Acut]

If you only need to show the results, than any of the three ideas is fine.

If you need to demonstrate the experiment in front of a public, choose either antacid or aspirin. Orange juices, even commercial ones, will show variations of ascorbic and citric acid concentration, so the results you will get can be quite unpredictable. Medicines have a more stable composition.

I would go for the antacid, since I'm quite methodic and would perform the same experiment a lot of times before doing it in front of a public. Antacids are cheaper, so I could buy many of them and test beforehand.

 

[Acut]

Ah - almost forgetting.

Antacids exhibit plenty of chemical phenomenon.

A)Get some phenolphthalein, sodium carbonate and sodium carbonate.
1)Prepare a solution of sodium carbonate. Drop some phenolphthalein. It gets red, showing sodium carbonate solutions are quite basic.
2)Prepare a different solution, with roughly the same concentration as in 1, but this time use sodium BIcarbonate. Add phenolphthalein. It gets pink, showing sodium bicarbonate solutions are basic, but not as basic as sodium carbonate. Why? (If you can't answer why, send me a private message or post in this thread)
3)Now prepare a solution of antacid, of roughly the same concentration as 2 and 3. Add phenolphthalein. It will likely get somewhere between pink and red, sinc most antacids are a mixture of sodium carbonate and sodium bicarbonate.

NOTE: You can prepare sodium carbonate solutions by heating sodium bicarbonate solutions.
2NaHCO3 -> Na2CO3 + H2O + CO2

(This decomposition is the reason why sodium bicarbonate is used to make cakes grow)

B) Get some ammonium hydroxide and phenolphthalein.
1)Add ammonium hydroxide to water and drop phenolphthalein. It should get deep red/pink. If it doesn't, add more ammonium hydroxide. But don't add too much.
2)Now add some antacid (use effervescent antacids). The red/pink collor disappears! It means that the solution got more acid with the antacid! Isn't it amazing? Why does it happen? Are drug companies fooling us? Again, if you don't know why (hint: it's related to buffer solutions), PM ou post in this thread. Another question: why using a buffer instead of a pure base?

Have fun!

 

[NicholasAllen]

Ah - almost forgetting.

Antacids exhibit plenty of chemical phenomenon.

A)Get some phenolphthalein, sodium carbonate and sodium carbonate.
1)Prepare a solution of sodium carbonate. Drop some phenolphthalein. It gets red, showing sodium carbonate solutions are quite basic.
2)Prepare a different solution, with roughly the same concentration as in 1, but this time use sodium BIcarbonate. Add phenolphthalein. It gets pink, showing sodium bicarbonate solutions are basic, but not as basic as sodium carbonate. Why? (If you can't answer why, send me a private message or post in this thread)
3)Now prepare a solution of antacid, of roughly the same concentration as 2 and 3. Add phenolphthalein. It will likely get somewhere between pink and red, sinc most antacids are a mixture of sodium carbonate and sodium bicarbonate.

NOTE: You can prepare sodium carbonate solutions by heating sodium bicarbonate solutions.
2NaHCO3 -> Na2CO3 + H2O + CO2

(This decomposition is the reason why sodium bicarbonate is used to make cakes grow)

B) Get some ammonium hydroxide and phenolphthalein.
1)Add ammonium hydroxide to water and drop phenolphthalein. It should get deep red/pink. If it doesn't, add more ammonium hydroxide. But don't add too much.
2)Now add some antacid (use effervescent antacids). The red/pink collor disappears! It means that the solution got more acid with the antacid! Isn't it amazing? Why does it happen? Are drug companies fooling us? Again, if you don't know why (hint: it's related to buffer solutions), PM ou post in this thread. Another question: why using a buffer instead of a pure base?

Have fun!

sounds great, but your correct that I don't know (about the buffer solution thing), so an explanation would be wonderful :) thanks!

 

[Borek]

Do you know how to calculate pH of solution containing both NH₃ and NH₄⁺? (this is the buffer Acut referred to).

Do you know how to calculate pH of the carbonate solution? Bicarbonate solution?

If not, check here:

http://www.chembuddy.com/?left=pH-calculation&right=toc

--

 

[ForeverOrchid]

NOTE: You can prepare sodium carbonate solutions by heating sodium bicarbonate solutions.
2NaHCO3 -> Na2CO3 + H2O + CO2

(This decomposition is the reason why sodium bicarbonate is used to make cakes grow)

^If we were to burn NaHCO3 to try and find the mass of the Na2CO3, do we make sodium bicarbonate into a solution with distilled water before we burn it?

 

[Borek]

f we were to burn NaHCO3 to try and find the mass of the Na2CO3, do we make sodium bicarbonate into a solution with distilled water before we burn it?

Not sure what you are asking about, but assuming I got it right - yes.

But you better elaborate on what you mean.