Naked Science Forum

Non Life Sciences => Chemistry => Topic started by: tazzems on 04/10/2007 15:30:25

Title: testing for nitrogen dioxide?
Post by: tazzems on 04/10/2007 15:30:25

Hi

Can you help a couple of oldies lost trying to do chemistry homework please?

we need to make nitrogen dioxide, which we know how to do, so assuming we have 3 small glass containers of the gas how do we test it to prove that it is nitrogen dioxide?

Thanks in advance.
Emma and Dawn
xx

Title: testing for nitrogen dioxide?
Post by: tazzems on 04/10/2007 15:48:07

Also what should happen with either a lighted or glowing splint if we add it to the nitrogen dioxide?

Title: testing for nitrogen dioxide?
Post by: eric l on 04/10/2007 15:51:46

Two major indications :

• the colour (reddish brown)
• the smell ("biting" - but don't inhale too much as it is very toxic)

As for the second question :  I'm not sure at all.  NO₂ is not as strong an oxidizing agent as concentrated nitric acid, and surely less oxydizing than pure oxygen.

Title: testing for nitrogen dioxide?
Post by: tazzems on 04/10/2007 16:10:18

Thankyou very much hun.

we will be testing with blue litmus paper too, which should turn red.

We are assuming that limewater will turn cloudy?

Title: testing for nitrogen dioxide?
Post by: lightarrow on 04/10/2007 19:41:41

Quote from: tazzems on 04/10/2007 16:10:18

We are assuming that limewater will turn cloudy?

Not at all; on the contrary, if limewater is initially slightly cloudy, NO₂ will make it more clear.

If you want to know how exactly it looks NO₂, you only have to drop a copper coin in HNO₃.

Title: testing for nitrogen dioxide?
Post by: DrDick on 05/10/2007 20:54:45

You could try cooling the gas down.  Two brown NO2 molecules will combine to form one colorless N2O4 molecule.  Cool it in ice and you will get a less intense color.  Cool it more and the color will go away.

Elemental bromine also has a reddish-brown vapor.  If you cool that, however, in order to get rid of the color, you have to condense it into a brown liquid.

Dick