chemistry paper 2

precipitiation and colour change

• you put sodium thiosulfate into a clonical flask and put in hydrochloic acid also.
• place this flask onto a white tile with a black cross in the centre of it 
• swirl the solution slowly and time how long that it takes to make the cross disappear when a white precipitate form (when it goes cloudy)
• stop the clock once the cross has diserpeared
• change the concentration of the sodium thiosulfate each time you repeat the investigation and record your results
• each concentration should take a different amount of time
• the control variable would be the amount of sodium thiosulfate and the person who is carrying out the investigation because the investigation can be very subjective
• the independant variable will be the concentration of the sodium thiosulfate
• the dependant variable will be the time that it takes for the cross the no longer been able to be seen.

reversable reactions

• reversable reactions will reach equilibrium
• when the forward reaction is exactly the same as  the backwards reaction the reaction has reached equilibrium
• if the equilibrium is on the right that means that the concentration of the the reactants is more than the reactants
• if the equilibrium is on the left the concentration of the reactants is greater than that of the products
• the position of the equilibrium depends on the following conditions:
•                    temperature
•                    pressure
•                    concentration
• if a reversable reaction is endothermic in one direction then it will be endo thermic in the other and visa versa

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