Problem with Sodium Nitrite And Glacial Acetic Acid Lab

[Evanone]

Hi. The instructions were to have 2 test tube filled with 10 mL of water in each. Then dissolve 3g of NaNO2 (sodium nitrite) in each test tube. Only take 1 of the test tube and put it in an ice bath so it reaches 0 degrees C. Insert 5 mL of Glacial Acetic Acid into the cold solution. You just leave the other test tube alone.

 

After these procedures i noticed that the top half of the cold solution was bubbling and had a light bluish color. The bottom of the tube stayed clearish.

 

The point of the lab is to figure out why the colors of the 2 test tubes varied.

 

My opinion is that the NaNO2 and HC2H3O2 had a double replacement reaction making HNO2 and NaC2H3O2. My thought is that the Nitrous acid is the cause of being why the top of the test tube was light bluish. Can anyone confirm? Are these products from my reaction correct?

 

Some other things I'm wondering is why did i have to make the solution 0 degrees Celsius? Why was the light blue part of the test tube bubbling?

 

Thanks in advance for your help.

[Darkblade48]

From another forums, where either you, or other classmates that are doing the same homework as you...

 

Originally posted by chemoleo

You brought it to 0 deg C to avoid decomposition of HNO2 (nitrous acid) as it is thermally very unstable. The bubbles you saw are most like decomposing HNO2, producing NO gas which reacts with air to produce NO2.

Yes your products are correct.

The reaction is no different to HCl reacting with Na2CO3, the stronger acid liberates the weaker one, and since H2CO3 is badly soluble in H2O, you get CO2 gas...

[woelen]

The acetic acid is strong enough to cause formation of nitrous acid. Nitrous acid (HNO2) is quite unstable. It has the following equilibrium reaction:

 

2HNO2 <---> N2O3 + H2O

 

The compound N2O3 is blue.

 

N2O3 decomposes very easily:

 

N2O3 <---> NO + NO2

 

NO is bubbling out of solution. NO2 reacts with water, to form HNO3 and more NO (you are invited to derive the reaction equation yourself).

 

If the temperature is too high, then the decomposition of N2O3 is going faster and NO is produced at higher speed, and the HNO2 hence disappears quickly.

[Evanone]

Thanks very much for the help.

 

i only have a few more questions.

 

What chemical principles or theories were involved?

 

What kind of experiment is this? What group?

 

Is there any other type of a reaction then a double replacement reaction?