Rates of Reaction SAC: Sources of error?

[lauzy358]

For our extended experimental we looked at equilibria and all that.
Just wondering if someone could help me out with spotting the sources of error possible here. I didn't pick up much =/
(Sorry the method's kinda of sketchy. I tried to Google it but the pracs weren't as simplistic as the one we did at school. +I'm tired =P. If it needs more detail let me know.)

Experiment 1.
[Co(H2O)6]2+ + Cl- = [CoCl4]2- + H2O

• [Co(H2O)6]2+(s) and HCl(aq) are mixed in a beaker. Stir.
• The resulting solution is poured into two test tubes.
• One test tube is placed in an ice bath, the other in a beaker with hot water.
• Watch for a reaction.

Experiment 2.
Fe3+ + SCN-(aq) = [Fe(SCN)]2+

• Make up a solution of Fe3+ and SCN-.
• Pour into test tubes.
• To each test tube add: ferric chloride; potassium thiocynate; NaF or AgNO3
• Watch for a reaction.

Experiment 3.
2NO2 = N2O4

This one was set up for us. All we had to do was go to the fume cupboard/hood, put on gloves & place pressure on the syringe or reduce pressure. Then note observations.

So, sources of error

• Temperature not being constant in experiments 2/3 - affecting rate of reaction
• Precision when making up solutions - concentrations need to be relatively accurate so colours are
• for #3, gas escaping? screws with colour intensity.
• #3, not applying pressure/reducing pressure quick enough. (kind of stupid though 'cause we could always try again if we hadn't noticed a change)

Any others? =S

ty =]