Pipet 25 mL aliquot of the KBrO3 solution. Introduce 2 to 3 g of Kl and about 5
ID: 1073165 • Letter: P
Question
Pipet 25 mL aliquot of the KBrO3 solution. Introduce 2 to 3 g of Kl and about 5 mL of 3 M H2SO4. Immediatly titrate with Na2S2O3 until solution is pale yellow. Add 5 mL of starch indicator and titrate to the disappearance of the blue color. Calculate the concentration of the thiosulfate solution. BrO3- + 6I- + 6H+ --> Br- + 3I2 + 3H2O *The sodium thiosulfate solution was said to be 0.05 M and to use about 12.5 g of Na2S2O3*5H2O per liter of solution. *In preparing the sodium thiosulfate, we had to dilute it to 0.1 M *Volume of the thiosulfate was 42.84 ml in the titration, for the back-titration we used 0.37 ml. Is this the information you needed?
Extra reactions;
2I- --> I2 + 2e-
I2 + 2S2O3 2- --> 2I- + S4O6 2-
Explanation / Answer
Na2S2O3 solution = 0.05 M
From the given data
moles of Na2S2O3 used = 0.05 M x 42.84 ml
= 2.142 mmol
moles of I2 = 2.142/2
= 1.071 mmol present in solution
So,
moles of KBrO3 = 1.071/3
= 0.357 mmol present
mass of KBrO3 = 0.357 mmol x 167 g/mol/1000
= 0.06 g