re: HSC Chemistry Marathon Archive
Next Q:
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.
Ceebs adapting to the question but this is straight out of my prac notes (I need to update them - but here's the whole prac):
2.1 Modelling an Equilibrium Reaction
Aim:
To model an equilibrium reaction.
Equipment:
• 2 x 100 ml Measuring Cylinder
• 10 ml Graduated Pipette
• 2 ml Pipette
Method:
1) Label the two measuring cylinders; one marked “A” and the other “B”.
2) Place 100 ml of water in “A” and 0 ml of water in “B”.
3) Place the larger pipette upside down into “A” so that it rests vertically on the bottom, seal it tightly by finger pressure and transfer its contents to “B” without spillage. Place the smaller pipette upside down into “B”, seal and transfer the contents to “A”. This is one complete transfer cycle, and the volumes present in both “A” and “B” must be recorded.
4) Continue with a series of transfer cycles until a state of equilibrium is achieved (i.e. There is no further change in the volumes in “A” and “B”).
Safety:
The glass pipettes are very fragile and if broken may cause harm. A teacher should be immediately notified if this were to happen. Furthermore, if water were to be spilled on the floor it should be immediately dried so as to avoid a slipping hazard.
Discussion/Conclusion:
The experiment began with all the water in “A”, but at a point in time, both water levels were constant despite water still being transferred back and forth, which is representative of the concept of dynamic equilibrium. The ratio of Volume B : Volume A at equilibrium was roughly a ratio of 1 : 1, and was not dependent on the starting volumes nor total volume of water in the system. The system was closed and the macroscopic properties were constant at equilibrium. In this experiment the measuring cylinders A and B acted as the reactants and products respectively, whilst the large and small pipettes represented the reaction rates. Appertaining to this, increasing the rate at which the water was transferred from one measuring cylinder to another via the pipettes, models the action of a catalyst. The transfer of liquid from “A” to “B” modelled the forward reaction, whilst the transfer of liquid from “B” to “A” modelled the reverse reaction. Overall, this experiment was a successful model for an equilibrium reaction, barring the minor spillages of liquid which would go against Le Chatelier’s Principle in that nothing enters or leaves a system at equilibrium.
We also see trends in changing pH of bodys of water such as lakes. 
This can show the presence of oxides of sulfur as it is acidic. Structures are also being destroyed which is another effect of acid rain. Since the industrial revolution this trend has been increasingand shows the evidence of an increase in concentration of sulfur dioxide in the atmosphere.
