2002 hsc q 28 (1 Viewer)

[Beats]

Hey guys- this was a really difficut question (for me) to answer, even though we actually did the prac:
During your practical work, you performed a first-hand investigation involving an equilibrium reaction
i outline the procedure you used
ii Explain how you analysed the equilibrium reaction qualitatively

What we did was heat/ cool and add ethanol/water (fresh sample) to some COCl2 in a testube and observe colour changes. I understand there was an equilibrium reaction involved - but what do i write in the procedure- just about the temp and concentration 'stresess' that we applied? - seeing as though we didn't really do anything to actually set up the equilibrium Any help would be greatly appreciated (escpecially if anyone did the same prac- or if they could help out with an easier one) Thanks for your time.

 

[mojako]

basically yes. just mention the colour changes as u increase the temp.. (from red to purple), and changes to red again when u cool it down again.
mention how u heat it (using bunsen), draw diagram if the number of marks sounds appropriate

u analyse the equil qualitatively just by observing the colour change

dont forget to mention the eqn.
just for other ppl to know, the equil is
[Co(H2O)6]2+ (aq) + 2Cl- (aq) <--> Co(H2O)4Cl2 (aq) + 2H2O (l)
[Co(H2O)6]2+ is maroon
Co(H2O)4Cl2 is dark blue
note: it's Co not CO (carbon and oxygen)
Co(H2O)4Cl2 is basically CoCl2 when its dissolved in water, i.e. in aqueous form.

the conc which can be played around with is
-> the water conc (add more water; add ethanol to decrease water becoz it binds the water molecules and decrease the amount of free water molecules.. u dont heat it to evaporate becoz it changes temp)
-> the Cl- ion conc.. u can add HCl to increase.. add more water to decrease its conc

 

[beta-omega]

yeah, basically u've got the main points of it. About setting up an actual equilibrium, the other class did in fact set one up. They added water until the actual equilibrium was found.
The actual equilibrium colour was purple, and it shifted to the Co(H2O)4Cl2 side, being blue, and the [Co(H2O)6]2+ side being pink or maroon.

A good way of describing this prac is to say that u set up 6 of them in a test tube rack (7 if you include a control), and compared the colours of all six. This method is more effective than just doing one at a time. Qualitative analysis of the eq reaction was through repeated use of 'stress' on the system with and ending up with the differing colours when one 'stress' was applied.