Iodine Clock Flashcards
what does the continuous monitoring method involve?
- pipette a sample of a mixture to excess sodium hydrogen carbonate.
- start stopwatch.
- withdraw samples at regular intervals e.g. 3 minutes. repeating the process.
- titrate with sodium thiosulphate adding starch indicator near the end.
- use results to plot concentration against time on a graph.
what acts as a catalyst in the continuous monitoring method?
H2SO4
why are large excess of H2SO4 and propane used in continuous monitoring?
so you can measure the influence of iodine.
why should the continuous monitoring experiment be carried out in a well ventilated room?
because sodium thiosulphate releases SO2.
how is rate measured in the iodine clock reaction?
by measuring how long it takes to produce a fixed amount of iodine.
what is the equation for the reaction of potassium iodide and potassium persulphate?
S2O8 2- + 2I- –> 2SO4 2- + I2
what varies in the iodine clock reaction?
the concentration of iodine
what do you calculate the order of in iodine clock?
order w.r.t. all reactants
outline the iodine clock method (3):
- sodium thiosulphate and starch added to an excess of hydrogen peroxide and iodide ions in acid solution.
- start a stopwatch.
- when solution goes bule/black, stop stopwatch.
continuous monitoring is also known as …?
the initial rates method.
what is the rate of reaction proportional to?
1/T
Errors in the iodine clock reaction?
- starch indicator effects concentrations. thus the amount they change over time.
- inaccurate timing? two people time simultaneously and take an average.
assumptions in the iodine clock experiment: (3)
- conc. of each reactant doesn’t change significantly over the time period.
- temperature stays constant.
- when the end point is seen the reaction hasn’t proceeded too far.
what can cause an increase in rate of reaction throughout an experiment?
the reaction is exothermic.
