Determination of the Product of a Redox Reaction: Reaction of Bromate and
TA: Daniel Bouchard
Date Performed: Thursday, January 16, 2014
Date Submitted: Wednesday, January 22, 2014 Introduction
Titration is a key method of chemistry that can be used in many different ways to help
uncover unknown amounts of products. One way titration is used is to determine the presence of
Vitamin C in juices. This helps to establish the nutrition values that certain juices have or lack.
The process includes using iodine and iodate solution in a redox titration with a starch indicator
acting as the endpoint of the titration .
The goal of this lab was to identify the unknown product of the reaction and complete the
redox reaction equation.
(1) BrO3 + NH3OH + Br +?
This goal was accomplished by using a known excess amount of bromate and a known
amount of Hydroxylammonium. Hydroxylammonium acted as the limiting reagent while the
Bromate reacted with potassium iodide solution.
- - + - -
(2) BrO + 3I + 6H O 3 Br + 3I +39H O 2
The rest of the Iodine was titrated with thiosulphate until an endpoint was reached as indicated
by the starch indicator. Knowing the amount of bromate initially and the excess, the reacted
bromate could then be calculated.
(3) I3+ 2S O 2 32- 3I + S O4 62-
Finally, to find the unknown product, the electrons transferred could be calculated by the moles
of the reactants and the oxidation states.
Refer to the lab manual for standardized procedure . Deviations included using precise
concentrations of the following reactants, 0.0200 M of NH OHCL, 0.0200M of KBrO
3 3 and 0.1000 M of Na S2 2. 3ew techniques that were used included a specific type of titration
called iodometric titration. This technique uses iodine ions to indicate the endpoint of the
titration. In this case, the appearance of the iodine in our solution (as observed in Erlenmeyer
flask by the yellow color) indicated the end of the titration.
NH O3Cl Volume: 10mL
KBrO 3 Flask 1: (burette readings)
(0.0200±0.0002M) Initial: 11.21mL; final: 31.15mL
Initial: 10.25mL; final: 30.15mL
Initial: 31.74mL; final: 51.64mL
Na 2 2 3 Flask 1: (burette readings)
(0.1000±0.0005M) Initial: 10.71mL; final 24.54mL
Initial: 20.52mL; final: 34.75mL
Initial: 34.75; final: 50.46
Table 1. Data Collected Table 2. Calculating the average amount of KBrO reacte3.
1 (a) Given:
Volume KBrO = 0301994L
Concentration KBrO = 030200M
n= C x V
n= (0.0200M) (0.01994L)
n= 3.99 x 10 mol of KBrO initi3lly
Volume Na S 2 2 0301383L
Concentration Na S 2 2 031000M
n= C x V
n= (0.1000M) (0.01383L)
n= 1.383 x 10 mol of Na S O 2 2t 3eacted.
It is important to know the amount of Sodium thiosulfate in the reaction because from it, the amount of excess amount of KBrO can be dete3mined. From the
balanced equations, the moles of Sodium thiosulfate can be divided by 6 because it
takes 1 BrO to produce 3 Iodine’s, and 3 Iodine’s produces 6 Sulfates.
1.383 x 10 /6= 2.3 x 10 mol of excess KBrO
In order to find the amount of KBrO that actually reacted, the excess amount must
be subtracted from the total amount that was present initially.
∴ 3.99 x 10 – 2.3 x 10 = 1.69 x 10 mol KBrO that reacted. 3
2 Total amount of reacted KBrO = 1.61 x310 mol.
3 Total amount of reacted KBrO = 1.36 x310 mol. -4
Average The average of KBrO that r3acted throughout the 3 trials was:
(1.69 x 10 + 1.61 x 10 + 1.36 x 10 )/3 -4
= 1.55 x 10 mol of reacted KBrO 3
(a) To find oxidation state of Bromine in the compound BrO , let x be the 3xidation state of Br;
x+ (-6) = -1
this is the oxidation state of Br. In order to get a -1 charge of Br in the reactants side, each
Bromine atom in BrO must ga3n a total of 6 electrons.
(b) Moles of electrons transferred is the average amount in mol of BrO found in questi3n 1
multiplied by 6 because that is how many electrons must be transferred by each Bromine atom.
The purpose of this step is to find how many moles of electron