Polymers

Read our general notes on Risk Assessment

I'm doing my individual investigation about the kinetics between bromide and bromate(V) ions. I have completed the experiments on finding the order of reaction by varying the concentration of bromate(V), bromide and sulphuric acid.
Now, I am trying to find suitable catalysts and calculate the order of reaction respect to the catalysts. The catalysts I used are Fe(III) and Cr₂O₇^2-. I have completed a set of experiments and the order of reaction respects to Fe(III) is apparently first order. However, when I plotted a graph of initial rate against concentration/conc²/conc³ of Cr₂O₇^2-, it doesn't show a straight line. I have repeated the experiment several time but it still doesn't work. So can I ask what should be the order of reaction respect to Fe(III), Cr₂O₇^-?

Ulex replies
 
I think your choice of prospective catalysts is open to doubt. The mechanism of the reaction does not involve a straightforward rate-determining step consisting of a collision between bromide and bromate ions. Both of these are believed to be converted into their respective acids by reaction with hydrogen ions from the acid reagent.
 
Anything which reacts with either of the two bromine-containing ions will therefore interfere with this mechanism and effectively introduce a new reaction.
 
I suspect that the dichromate(VI) ion does this, reacting with the bromide ions, giving bromine but leaving the bromate(V) ions unreacted. This could be the reason for your anomalous results.

Risk assessment
Before attempting any practical work based on the advice and suggestions on this website, you must do the following. Identify any hazards, assess the risks from these hazards, and then decide appropriate control measures to reduce the risks. You must have these approved by those in authority in your school or college laboratory. Do not rely on what is said on this website. For further guidance see our tutorial on Risk Assessment.

back to Polymers

---

Rate this page or react
Share your views on this page, 0 ratings so far

---

updated: 01 April 2008