[MilchstrabeStern]

Hello,

I believe this is a common lab in a general chemistry course.

I am trying to help a friend with her lab, and although I am pretty good with chemistry, I am only in my first year of college, and all my memory is from my High School AP class. I am a Chemical Engineering major though.


The lab procedure is to take 1 Molar solutions(so the salts are first dissolved in distilled water) of CaCl2 and NaCl.

You then take 2 ml of ONE of these and place it in a graduated cylinder.

The next step is to add 23 ml of Carbonic Acid (also known as Alka Seltzer or H2CO3).

Then you place a stopper in, and flip the graduated cylinder over and measure the rate at which the gas is created.


You do this for both 1 molar solutions of the salts, and once with distilled water, so you have a total of 3 test.


My question is, what is going on here? What is the Carbonic Acid reacting with to release the gas (CO2?). How do the salts effect the rate of this decomposition, or release and gas, and why?

Any help would be Greatly appreciated!

Thanks Guys!

-Bryan

[Blueshawk]

It may be that you are creating Cl gas.  both salts of Cl, so it may be that that is what is going on.

I am not 100% sure, I am not familiar with this lab.

2NaCl(aq) + H2CO3(aq) -> 2Na+(aq) + HCO3-(aq) + Cl2(g) + H3O+   ??

CaCl2(aq) + H2CO3(aq) -> Ca+2(aq) + HCO3-(aq) + Cl2(g) + H3O+  ??

[Borek]

The next step is to add 23 ml of Carbonic Acid (also known as Alka Seltzer or H2CO3).

Something is wrong here. Alka Seltzer is not a carbonic acid. Also it will be very difficult to add a carbonic acid solution, as carbonic acid is unstable and decomposes by itself. You may add water saturated with CO₂, but then it will be pretty difficult to know what was the CO₂ concentration.

Are you sure about the procedure and reagents used?

[Borek]

I am not 100% sure, I am not familiar with this lab.

You are completely, awfully wrong.

[sdekivit]

It may be that you are creating Cl gas.  both salts of Cl, so it may be that that is what is going on.

I am not 100% sure, I am not familiar with this lab.

2NaCl(aq) + H2CO3(aq) -> 2Na+(aq) + HCO3-(aq) + Cl2(g) + H3O+   ??

CaCl2(aq) + H2CO3(aq) -> Ca+2(aq) + HCO3-(aq) + Cl2(g) + H3O+  ??

it's just a replacement reaction resulting into Na2CO3 and HCl(aq) in my opinion.

[Blueshawk]

You are completely, awfully wrong.

Thanks for letting me know the truth..I like honesty....And I figured I was wrong...But it was fun typing it

From what was originally there..I wasnt sure how CO2 would be produced..so i guessed Cl gas

But thanks again...HATs off to Borek !

[MilchstrabeStern]

Well I thought it was Carbonic Acid,but maybe not. I do know that it is Alka Seltzer water though.

I do know that a gas is being created (it's certianly not chlorine gas, that might be a little dangerous lol). I thought it was CO2 guys, but if I am wrong I'm sorry. I don't have the lab sheet, it's my friends.

I do know that the salts effect the rate that the gas is produced tho.

[MilchstrabeStern]

Citric acid (C6H8O7) and sodium bicarbonate (NaHCO3) is what i found to be the main components of alka seltzer TABLETS, not sure if this is the same for alka seltzer water tho.

[Blueshawk]

What education level is this lab for...?

I did not think of it at first..but Cl gas is a little dangerous for beginners.

[MilchstrabeStern]

I dont think Cl gas is being produced, and this is only a second semester college general chemistry course.

[Blueshawk]

No Cl is most likely not produced..i did a little browsing to see how easliy it can be made.

Most likely CO2...looking at what you have for the components of alka seltzer,

though I am not sure on the exact mechanism.

[MilchstrabeStern]

Okay guys i've confirmed what we're dealing with with the Alka Seltzer WATER is Carbonic Acid (H2CO3) which decomposes into H20 and C02.

How does the Salt affect this decomposition?

[Donaldson Tan]

Ca2+ has higher polarising power than Na+, so Ca2+ is able to distort the electron distribution of carbonic acid to a greater extent than Na+. This means Ca2+ catalyses the breakdown of carbonic acid to carbon dioxide to a greater degree than Na+.

[MilchstrabeStern]

Okay so you have Na+ Cl-

and you have Ca +2 and 2 Cl -

So NaCl and CaCl2 are polar molecules?

Also their data said that adding Carbonic Acid to distilled water had  the fastest reaction rate, how does that work? Bad data?

**Edit**

or wait, when you make the NaCl and CaCl2 solutions, are the chlorines being sepearted and what is the Na and Ca bonding to?

[Blueshawk]

Well when NaCl is placed in water it dissociates to Na+ and Cl-.

What happens then is the oxygen in the water molecules are attracted to, but does not bond to, the Na+.
Since the O in water is partially negative.

With Cl-, the H's in water surround the Cl-, since the H's have a partial positive.

So if it is indeed the effects that the Na+ and Ca+2 that affect the rate, then it could be seen that the Na+ and Ca+2 have a harder time effecting the rate since they are hindered my the attraction of the water molecules.
And water does not affect the rate as much with the salt in solution since it's partially positive H's are hindered by the attraction to Cl-.

So for distilled water, it may be that the partial positives on the H's have a similar affect as the Na+ and Ca+2, but more effective

Anyone have any other comments???