# Redox Titration Using Sodium Thiosulfate Solution Report

**An example of redox tiration using sodium thiosulfate report is available in the following webpage:**

www.usm.maine.edu/chy/manuals/116/text/RdxTi.html

The following is an excerpt from the webpage where you can go to the link provided and download the Report form(a PDF file format). You can use Adobe reader to view the Report form file. It is only A Report form however, so you have to supply the data from your laboratory experiment and review your lectures on the required computations.

**Procedure, **

Download and print the Procedure for this experiment. Study it carefully after reading this page. In your lab notebook, translate the procedure into step-by-step instructions for your lab work. Leave room for alterations in procedure, and for observations. Also prepare spaces or tables in your lab notebook to receive the data you will collect in lab. Bring the printed procedure and your prepared lab notebook with you to lab. Once per semester, you might earn a free perfect quiz score for bringing a well-prepared notebook.

**Report**

Download and print the Report Form for this experiment. Bring it with you to lab.

If it is not convenient for you to download the report form online, you might wish to print the form below:

** Redox Titration: Comparing the Strengths of Bleaches**

Print this form and bring it with you to lab.

I. Information, Data, and Observations

In CHY 114, you recorded data and observations in specified sections of a Report Form like this

one. In this course, you will keep complete records of your lab work, including actions,

observations and data, in your Laboratory Notebook. Your records should be sufficiently

complete to enable another student with your chemistry background to repeat your work and

compare their own actions, observations, data, and results with yours, using only your lab

notebook.

Do not keep lab records on this form. You should have no reason at all to mark on this form until

after lab and after completion -- in your lab notebook -- of all calculations requested in this form.

After you have completed all the calculations and tabulated the results in your lab notebook, you

will transfer selected results and sample calculations into the spaces and tables provided below.

Your name: ________________________ Your instructor: ___________________

CHY 116 Report

page 1

II. Calculations and Results

In your lab notebook, immediately following your records of laboratory work and your lab data,

carry out the following calculations to obtain the final results of this experiment. In your lab

notebook, label each section of calculations the same as the sections of the Procedure.

Calculations for Part 2.

Standardizing Sodium Thiosulfate Solution

1. Calculate the number of moles of iodate ion in the 10.00 mL of 5.00 x 10-3 M KIO3 that you

use in each titration during Part 2. Transfer the answer to the space below. Remember to show all

calculations clearly in your lab notebook. Beside the answer below, enter the page number where

your instructor can find your calculations.

ANSWER: ___________ mol IO3- (CALCULATIONS ON PAGE # ___ .)

2. Use the balanced equations for this titration (Equations 3 and 2) to determine the number of

moles of thiosulfate ions that react with one mole of iodate ions.

ANSWER: ___ mol S2O32- per mol IO3- (PAGE # __ )

3. Use answers 1 and 2 to calculate the number of moles of thiosulfate ion that would be required

to react with the iodate ions described in question 1.

ANSWER: ________ mol S2O32- (PAGE # __ )

4. Answer 3 is the number of moles of thiosulfate ion in the volume of thiosulfate solution that

was required to titrate the iodate solution to the endpoint. Use the net volume of each titration to

compute the molarity (M = mol/L) of your thiosulfate solution. Enter answers for the two best

runs.

ANSWERS: ________ M (run # __) and ______ M (run # __) (PAGE # __ )

5. For calculations in Parts 3 and 4 (below), use the average of the molarities in question 3 as

your thiosulfate molarity.

MOLARITY OF THIOSULFATE SOLUTION: ______ M (average of two best runs)

Your name: ________________________ Your instructor: ___________________

CHY 116 Report

page 2

Calculations for Part 3.

Determining of the Oxidizing Capacity of an Unknown

1. Use the equations for this titration (equations 1 and 2) to determine the number of moles of

hypochlorite ion that react with one mole of thiosulfate ions.

ANSWER: __ mol OCl- per mol S2O32- (PAGE # __ )

2. For each titration, use the net volume of titrant (thiosulfate solution), the molarity of the

titrant (Part 2, answer 4), and answer 1 above to calculate the number of moles of hypochlorite

ion in each titrated sample of unknown. Enter answers from the two best runs.

ANSWERS: ________ mol OCl- (run # __ ) and ______ mol OCl- (run # __ ) (PAGE # __ )

3. Calculate the mass of NaOCl in each titrated sample. Use answer 2 and the molar mass of

NaOCl: 74.44 g NaOCl/mol. Enter answers from the two best runs.

ANSWERS: ________ g NaOCl (run # __ ) and ______ g NaOCl (run # __ ) (PAGE # __ )

4. You weighed each sample of your unknown before titrating it. Use the mass of each titrated

sample and answer 3 for the corresponding run to determine the percent by mass of NaOCl in the

sample. Percent by mass is the number of grams of NaOCl per 100 g of the sample. Enter

answers for the two best runs.

ANSWERS: ____ % NaOCl (run # __ ) and ____ % NaOCl (run # __ )

(PAGE # __ )

5. Calculate the average % NaOCl from your two best runs.

ANSWER: ____ % NaOCl (PAGE # __ )

Use the answers to questions 2 through 5 to complete the table of titration data that you set up

for Part 3 in your lab notebook (See Procedure, Part 3). (PAGE # __ .)

Your name: ________________________ Your instructor: ___________________

CHY 116 Report

page 3

Calculations for Part 4.

Determining of the Oxidizing Capacity of a Commercial Bleach

Calculations in Part 4 are the same as those in Part 3.

1. For each titration of a bleach sample, use the net volume of titrant (thiosulfate solution), the

molarity of the titrant (from Part 2), and answer 1, Part 3 to calculate the number of moles of

hypochlorite ion in each titrated sample of bleach. Enter answers from the two best runs.

ANSWERS: ________ mol OCl- (run # __ ) and ______ mol OCl- (run # __ ) (PAGE # __ )

2. Calculate the mass of NaOCl in each bleach sample. Use answer 2 and the molar mass of

NaOCl: 74.44 g NaOCl/mol. Enter answers from the two best runs.

ANSWERS: ________ g NaOCl (run # __ ) and ______ g NaOCl (run # __ ) (PAGE # __ )

3. You weighed each sample of your bleach before titrating it. Use the mass of each titrated

sample and the corresponding answer 3 to determine the percent by mass of NaOCl in the bleach.

Enter answers for the two best runs.

ANSWERS: ____ % NaOCl (run # __ ) and ____ % NaOCl (run # __ )

(PAGE # __ )

4. Calculate the average % NaOCl in the bleach from your two best runs.

ANSWER: ____ % NaOCl (PAGE # __ )

5. Finally, recall that you diluted your bleach sample 1:10 before titration. Calculate the %

NaOCl in the original unknown, before dilution.

ANSWER: ____ % NaOCl (PAGE # __ )

6. What brand of bleach did you use? What is the percent NaOCl stated on the label. Do your

results confirm the label information?

Use the answers to the preceding questions to complete the table of titration data that you set up

for Part 4 in your lab notebook (See Procedure, Part 4). (PAGE # __ .)

Your name: ________________________ Your instructor: ___________________

CHY 116 Report

page 4

III. Questions

1. Write complete, balanced, net ionic equations for the following reactions:

a. The overall reaction describing standardization of thiosulfate solution using iodate solution

(combine equations 2 and 3). Your equation should reflect the molar ratio of thiosulfate ions to

iodate ions in the reaction, which should agree with Part 2, answer 2. Remember that elements and

charges must balance.

b. The overall reaction describing titration of hypochlorite samples with thiosulfate solution

(combine equations 1 and 2). This equation should reflect the molar ratio of hypochlorite ions to

thiosulfate ions in the reaction, which should agree with Part 3, answer 1). Remember that elements

and charges must balance.

2. Would the calculated percent by mass of NaOCl in a bleach be increased (I), decreased (D), or

not changed (NC) by each of the following errors? Circle your answer and then explain briefly,

showing how the error leads to the incorrect calculated value.

a. A small amount of bleach sample splashes up onto the side of the titration flask, and is never

washed down into the solution.

I D NC

b. A small amount of bleach sample splashes up onto the side of the titration flask, and is

washed down into the solution with distilled water before the endpoint is reached.

I D NC

c. The student forgets that the original bleach sample was diluted, and does not correct for this

dilution.

I D NC

Report

Hand in pages 2-5 of this Report, followed by the lab-notebook yellow sheets for this experiment.

Staple and hand in as a single package.

Ask your instructor whether you should include an abstract for this experiment. If so, it

should be the first page of your report package.

Your name: ________________________ Your instructor: ___________________

CHY 116 Report

page 5