Hi! I need help to finish this lab report...I have everything written down and calculated but I'm stuck figuring out how the amount of sodium thiosulfate reacted with Iodine and then the ratio between iodine and iodide...? U don't need to write the whole thing, I just need u to look at where I am at and help me answer the final step and finish the discussion and conclusion, everything else is done...and it's due tomorrow...can you do that, please?



Title: Project C – The stoichiometry of reaction.
30/06/2014

Purpose: Main purpose of the experiment is to obtain further experience in the application of
volumetric analysis, and to become familiar with another type of titration that involves redox
reactions (oxidation-reduction reactions). Particular focus of this experiment is to attempt to
determine the stoichiometry (i.e., the balanced equation for the equation 1) for the redox reaction
that occurs between iodate ions and iodide ions in the acid solution. Minor objectives are
calculating the proper amounts of solutes for both of the stock solutions (KIO3 and KI), and
carrying out the volumetric analysis by operating a burette as in the previous A3 experiment
(acid-base titrations).
By the end of the experiment we will determine the values of a,b,c,d, and e in the following
equation:
Equation 1: aIO-3(aq) + bH+(aq) + cI-(aq) ->
Iodate

Hydronium

iodide

dI2(aq) + eH2O(l)
iodine

water

Ion
Introduction: In this experiment we will perform another common type of titration analysis the
for redox reaction between iodate and ioded ions. A redox reaction is a chemical reaction where
two or more atoms or ions undergo a change in oxidation number. If the oxidation number of an
atom or ions is increased – oxidation occurred, and if the oxidation number of an atom or ion
decreased – reduction occurred. The processes of oxidation and reduction occur simultaneously,
and it is not possible to have a reaction in which only oxidation or reduction occurs.
In order to carry out the required experiment, we are going to use the two known stock solutions
of 1 – potassium iodate (KIO3) and 2 - potassium iodide (KI). By reacting a known amount of
potassium iodate (KIO3) with excess acidic potassium iodide (KI) we will later determine the
amount of molecular iodine produced (i.e. thereby determining the ratio of d:a, see Equation 1).
In order to find the required proportion of iodine vs iodate, we will titrate the iodine formed
against the solution of sodium thiosufate (Na2S2O3). See equation 2.
Equation 2: 2S2O32-(aq) +
Thiosulfate

I2(aq) ->
iodine

2I-(aq) +
iodide

S4O62-(aq)
tetrathionate

As the iodine/thiosulfate titration proceeds, the colour of the acidic solution will be changing
from its initial red-brown, through yellow, and then eventually to colourless. In order to obtain
the exact end-point of titration starch indicator is used because by doing just the titration of
iodine vs thoiosulfate the colour change is not sharp enough to be used for determining the endpoint of titration. The starch indicator is added to the acidic solution of iodine/thiosulfate when
the titrated colour appears very close to the end-point (pale yellow). The starch indicator will
turn the iodine/thiosulfate solution into blue/black colour when some concentration of iodine is
still present in the solution and it will give a sharp end-point by turning the solution completely
colourless, when the iodine completely reacts with thiosulfate.
Since the required amounts of stock solutions are not directly provided in the experiment
description, in order to proceed with the experiment, first, we will need to determine the required
amounts of both reactants from the given masses and the known required final concentrations of
both solutions. The required calculations will be obtained though the calculations of molarities
and molar masses in order to obtained the correct volumes and concentrations of both solutions.
Procedure: ref: Project C of the Chemistry 217 of the Home Lab Manual, pp.191 – 200.
Part A. Preparation of Stock Solutions and Reagents
1. 0.015 M Potassium iodate (KIO 3) stock solution was prepared by mixing the dry mass

(0.3282g, as was provided in the lab kit) of KIO 3 with the 100ml of tap water in the clean
dry 100ml volumetric flask and mixed until the dry mass was completely dissolved in the
water.
2. 1.0 M Potassium iodide (KI) stock solution was prepared by mixing the 8.3g of dry KI

(the mass of KI was weighed – out as it was instructed in the manual, p.194) with 50ml of
water in the clean dry 50ml beaker until the dry mass of KI was completely dissolved in
the water.
3. 25ml of 1.0 M Hydrochloric acid (HCl) solution. Note: this solution was commercially

manufactured and supplied.
4. 50 ml of 0.1000 N Sodium thiosulfate (Na 2S2O3) titration standard solution. Note: this

solution was commercially manufactured and supplied.
5. 1 small dropper of starch indicator solution. Note: this solution was commercially

manufactured and supplied.
Part B. Preparation of the Reaction Mixture
1. To prepare the acidic KI solution, a clean dry 125 ml Erlenmeyer flask (reaction vessel)

was obtained. Using clean dry 1ml volumetric pipette, a volume of 3ml of the 1.0 M KI
stock solution was transferred into an empty 125ml Erlenmeyer flask. Next, by using the

same 1ml volumetric pipette, a volume of 3ml of 1.0 M HCl was mixed with the 3ml of
KI solution in the 125ml volumetric flask. 6ml of the required reaction mixture was
prepared in the 125ml Erlenmeyer flask.
2. The 1ml volumetric pipette was rinsed with water.
3. Using clean 1- and 5-ml volumetric pipettes a volume of 6ml of the 0.015 M KIO 3 stock

solution was transferred into the reaction vessel (125ml Erlenmeyer flask), containing the
6ml of mixed acidic potassium iodide (Ki + HCl) solution.
4. The pipettes were rinsed with water for future use in the experiment.
5. The above procedure was repeated 3 times for the 3 trials of titration procedure.

Part C. Titration
The procedure used for titration in the Experiment A3 of the Chemistry 217 Home Lab Manual,
pp.116- 121 was followed, except for the following modifications:
1. 0.1000 N Sodium thiosulfate (Na 2S2O3) solution was used for titration during this

experiment instead of HCl used in the A3 experiment.
2. Starch indicator was added later in the titration process when the titrated colour was close

to the end point (pale yellow), and not in the beginning of the titration procedure as it was
done in the A3 experiment.
Results and Calculations:
Part A. Preparation of stock solutions and Reagents
1. Preparation of 0.015 M potassium iodate (KIO3) stock solution:
?

Mass of potassium iodate (KIO3) used – 0.3282g.

?

Molar mass of potassium iodate (KIO3) – 214 g/mol

? Moles of KIO3 = 0.3282g x 214 g/mol = 0.0015 moles of KIO3

Since Molarity = moles of solute/amount of total solution (L)
? Required amount of solution = 0.0015 moles KIO3/ 0.015 M KIO3
? amount required is 0.100 L or 100ml of KIO3
?

Concentration of the stock solution = moles of solute/volume of solution

? Concentration of KIO3 stock solution = 0.0015moles of KIO3/ 0.100 L

? = 1.5 x 10-2 mol/L
?

The resulted solution was colourless

2. Preparation of 1.0 M Potassium iodide (KI) stock solution:
?

Mass of potassium iodide (KI) used – 8.3g.

?

Molar mass of potassium iodide (KI) – 166 g/mol

? Moles of KI = 8.3g x 166 g/mol = 0.050 moles of KI

Since molarity = moles of solute/amount of total solution (L)
? Required amount of solution = 0.050 moles KI/ 1.0 M KI
? Amount required is 0.050L or 50ml of KI
?

Concentration of the stock solution = moles of solute/volume of solution

? Concentration of KI stock solution = 0.050 moles of KI/ 0.050 L
? = 1.0 mol/L
?

The resulted solution was slightly yellowish in colour.

3. Other reactants were supplied with the lab kit and no calculations were required.

Part B. Preparation of the Reaction Mixture
1. 3ml of KI and 3ml of HCL were mixed together in the 125ml Erlenmeyer flask (reaction

vessel). Colour of the solution became slightly orange/ light brown in colour.
2. 6ml of KIO3 stock solution were added to the acidic KI mixture in the 125ml Erlenmeyer

flask. The resulted solution became dark brown in colour.
3. The reaction mixture was prepared as described above 3 times for the 3 separate trials of

titration.
Part C. Titration
1. The burette was set up and prepared for the experiment as it is described in the Chemistry

217 Home Lab Manual pp. 115-119
2. Prior to the initiation of the titration experiment, the burette was rinsed and charged with

0.1000 N Sodium thiosulfate (Na2S2O3) until the top of the burette (17.0ml reading) and
was refilled in between trials as needed.

3. 125ml Erlenmeyer flask, containing the reaction mixture, was placed on the stand under

the burette, with the tip of the burette about 2cm below the rim of the flask.
4. The stopcock of the burette was slightly opened allowing the titrant solution to slowly

drip into the flask. At the same time, the flask was slowly swirled until the solution colour
became pale yellow, meaning the solution was coming close to its’ end-point
concentration stage.
5.

The stopcock was closed and 2 drops of starch indicator were added into the reaction
mixture. The mixture was mixed well until all the solution reached dark blue/black
colour.

6. Continued with the titration procedure until the reaction mixture became colourless

(reached the end-point of titration).
7. The 3 trilas were repeated identically as described in the above steps. Table 1 summarizes

the results from the 3 trials that were completed.

Table 1. Summary of the three trials

Initial reading of the
burette
Final reading of the
burette
Volume of the titrant
added

Trial 1
17.0 ml

Trial 2
17.0 ml

Trial 3
17.0 ml

26.6 ml

26.9 ml

28.0 ml

9.6 ml

9.9 ml

11.0 ml

After we have completed the titration procedure, we can now determine the values of a,b,c,d and
e that were missing the Equation 1:
aIO-3(aq) + bH+(aq) +
Iodate

Hydronium

cI-(aq) -> dI2(aq) + eH2O(l)
iodide

iodine

water

Ion
***This is the final equation that I need eventually come to:
IO-3(aq) + 6H+(aq) + 5I-(aq) -> 3I2(aq) + 3H2O(l)
but it needs to come somehow from the calculated amounts used in the titration…I have no idea
how…
Discussion:
Answers to Questions:
High altitude balloons used by Environment Canada to measure O 3 levels in the atmosphere also
use a similar idiometric titration where the iodine liberated is measured by back titration with
sodium thiosulfate. In this case the iodine is generated by oxidation of iodide by ozone:
O3 + 2I-(aq) + 2H+(aq) -> I2(aq) + O2(g) + H2O (l)
If 10000L of air were bubbled through an acidic iodide solution (at STP) and was then back
titrated with 19.4ml of a 1.2 x 10 -4 M Na2S2O3 solution to reach equivalence, what is the
concentration of ozone in that sample of air (in pump)?
?

Mole ratio from the reaction, between ozone and molecular iodine (I2):
1 mol of O3 is stoichiometrically equal to the 1mol of I2 (1:1)
Mole ratio between thiosulfate and molecular iodine (taken from the equation 2):

Conclusion: