Chemistry有關搵first order 的實驗(20分)

1. the function of the NaHCO3:
This is a base used to react with the hydrogen ion in the solution. This can consume most of the hydrogen ions so that the reaction is quenched(stopped).

2. did the iodine concentration change at a uniform rate?
it can be known from your experiment. (hunt: the rate of change should increase first and finally decrease)

3. is the rate of change of the iodine concentration dependent on the iodine concentration?
This is something u can say according to your experimental result. It should be found that they are independent on each other.

6.Does iodine take part in the rate determing stp of iodination of propanone?
If the order of reaction with respect to iodine is 0, that is Iodine does not appear in the rate equation, iodine would not be in the rate determining step.
The order of iodine should be calculated from your results.

8. why the starch indicator should be added to the solution near the end -point?
Starch indicates the presence of I2. Therefore, the solution would turn from dark blue to colourless across the endpoint.
The importance of adding the starch near the endpoint but not at the beginning of the reaction is that starch will combine with Iodine to form irreversible (i.e. some of the iodine cannot be tested, and the solution would not turn colourless) darkblue complex when the iodine concentration is high.

2007-01-31 21:07:24 補充：
H (aq) is a catalyst for this reaction. Without H (aq) the reaction rate would be extremely slow and concentration of I2 would not change significantly during titration.

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