[mcchem]

I did the iodine clock reaction using sodium metabisulfite and potassium iodate. As I understand it, increasing concentration is supposed to speed up your reaction rate. I did 10 trials. The first 5 I varied the concentration of metabisulfite and kept the iodate constant. Trials 6-10 I varied the potassium iodate and kept the meta constant. Can someone PLEASE help me understand why as I increased concentration, the reaction rate became slower?! For example in trial 6 I had 2 ml of sodium metabisulfite and 4 ml of potassium iodate, that only took 7 seconds. In trial 10 I had 2 ml of meta and 10 ml of potassium iodate and that took 17 seconds? I am so confused does anyone know what I did wrong? Increasing concentrations should have increased collisions and made the rate quite fast, but it did the opposite?? Please help :(

[Yusf]

Hmm, as you have increased the amount of reactant, the reaction is taking more time to stop. The rate of reaction is faster but time taken to stop is higher as more amount of reactant is available for reaction.

I hope that clears it up for u.

[kreysiz]

See, rate of reaction = rate constant*change in concentration of the reactant raised to some power.
The power to which the concentration term is raised is greater than zero but can be a fraction.It is called the order of the reaction and it can be determined only experimentally.