Rates of reaction - kinetics (A2)
Read our general notes on Risk Assessment
Hello, I am doing the experiment is between bromate(V) ions and bromide ions. I am analysing the effect concentration has on the rate. I know I have to change the concentration of potassium bromide but I read that I also have to change the concentration of sulphuric acid. Why is that? What is the reason of using sulphuric acid and why do I have to change it when changing the concentration, and by how much (e.g. same change as the potassium bromide?). Secondly, I am confused about how I am to figure out how much concentration and volume to use in the first place?
Igloo writes
Bromate(V) and bromide ions can only react in the presence of hydrogen ions:
BrO3-(aq) + 5Br-(aq) + 6H+(aq) -> 3Br2(aq) + 3H2O(l)
The purpose of your experiment is to find out something about the mechanism of this reaction, and, in particular, to determine the rate determining step. To do this you need to find the order of reaction with respect each of these ions, including, of course, the hydrogen ions. This is why you need to carry out a set of experiments in which you find out how the rate is affected by changing the concentration of sulphuric acid.
As to your second question, you will simply need to try out different concentrations of acid, whilst keeping the concentration of bromate(V) and bromide constant. If you are finding that your experiments are too fast, i.e. times are too short to measure accurately, then you will need to think about using lower concentrations. Safety is obviously an issue here, since some of these chemicals, e.g. potassium bromate(V), sulphuric acid and the bromine formed in the reaction, are hazardous. You will need to find out what sort of concentrations fall within a reasonable safety net. Note that we are not qualified to give safety advice on React and you must carry out your own risk assessment. As a rough and ready guide you could consider concentrations of all three in the region of between 0.05 and 0.50 mol dm-3. You don’t not mention the technique you are using so I can’t comment on the volumes to use.
Always carry out a risk assessment and check with your teacher before starting any practical work.
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 Rates of reaction - kinetics (A2)
Rate this page or react
Share your views on this page, 2 ratings so far
, rated at 
updated: 29 January 2006
