February 26, 2017

Homework Help: chemistry

Posted by khela on Tuesday, October 26, 2010 at 4:22pm.

Am doing a lab report on the determination of the product of a redox reaction: the reaction of bromate and hydroxylammonium ions.
here is the lab

In this experiment you will determine the equation of a redox reaction by the use of experimental data.

This is a reaction in which it is not obvious what products will be formed but by finding the relative number of moles reacting
you can deduce what reaction has occured.

The reaction is between bromate ions, BrO3(-) and hydroxylammonium ions NH3OH(+) in aqueous acid solution.
You assume that the bromate are converted to bromide ions, Br(-) (How can this reaction be shoed experimentally)

So the reaction that is being studied is:

BrO3(-) + NH3OH(+) ----> Br(-) + ?
If you know the number of moles of bromate consumed in the reaction and you know the oxidation states of Br in the reactant and in the product, then you can calculate the number of moles of electrons gained by Br in the reaction. (this must equal to the number of moles of electrons lost by the N of hydroxylammonium in the reaction. Knowing the number of moles of hydroxylammonium reacted, one can calculate the number of moles lost by N per hydoxylammonium reacted. This then allows you to determine the oxidation state of the N in the unknown product. In the acid solution, the following compounds of N and H and/or O can exist: NH4(+), N2H5(+), HN3, N2, N2O, NO, H2N2O3, HNO2, No2, No3(-).
It can be assumed that the N containing product of the reaction is one of these.
The experiment is arranged so that the hydoxylammonium is the limiting reagent and bromate is in excess. The amount of this excess is found by adding potassium iodide solution, which reacts with bromate:

BrO3(-) + 9I(-) + 6H3O(+) ---> Br(-) + 3I3(-) + 9H20

You can assume that nothing else reacts with the iodide ions. The resulting triioxide ions, I3(-), are brown in colour and can be
titrated with thiosulphate, S2O3^2(-):

I3(-) + 2S2O3^2(-) ---> 3I- + S4O6^2(-)
From the titration the number of moles of triiodide is determined. From the number of moles of triiodide and the two balanced equations above, the number of moles of excess bromate is determined. Subtracting the number of moles of excess bromate from the total number of moles of bromate used, gives us the number of moles of bromate consumed in the reaction. From this the N containing product can be identified and a balanced equation
for this reaction can be written.

i really don't understand what they talking about here really...i did the experiment and it was easy enough but i cant write a lab report... can sumone help me write out the purpose of this experiment. i wud really appreciate it.

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