The Student Room Group

A level chem

part a)
Excess potassium iodide solution was added to 25.0 cm3 of an aqueous solution of bromine.
Br2 +2I– 􏰄2Br– +I2
The iodine produced was titrated with sodium thiosulfate solution. All of the iodine
required 24.20 cm3 of 0.100 mol dm–3 sodium thiosulfate solution for reaction. 2S2O32– + I2 􏰄 S4O62– + 2I–

(i) Calculate the concentration of the aqueous solution of bromine.
the answer I got was 0.0484 which is right
now:


In another experiment, 100.0 cm3 of the same aqueous solution of bromine was treated directly with 0.00100 moles of sodium thiosulfate.
Excess potassium iodide was then added to the unreacted bromine.
The iodine produced required 16.80 cm3 of the 0.100 mol dm–3 sodium thiosulfate solution for reaction.
Deduce the mole ratio of S2O32– : Br2 and hence write a balanced equation for the reaction between thiosulfate ions and bromine.
State symbols are not required.

how do I do this
Original post by TrES2b
(i) Calculate the concentration of the aqueous solution of bromine.
the answer I got was 0.0484 which is right

how do I do this


Can you show us what you did for the 1st one, so that we can see where you have gone wrong?

Can you write the two half-equations for the thio reaction and the Br2 reaction?
Can you combine them together to make the overall redox reaction?

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