U8 Redox Titration Lab Final

U8 Redox Titration

Lab Final

By Jolene Kayser

​Include in Learning log:

1. Background​ & Safety

2. Procedures

3. Data Table​

4. Pre-lab questions

5. Post Lab question

   1. Set Up calculations (before lab)

      1. Must complete at least 3 set-ups

6. Reflection: What have you learned from labs this year​.

   1. minimum 5 sentences​

   2. think about lab techniques, content, organization, working in groups etc

​Background 1 of 2

Hydrogen peroxide, H2O2, is easily oxidized. It is used in commercial bleaching processes and in wastewater treatment plants as an environmentally friendly alternative to chlorine. Dilute solutions of H2O2 are used to bleach hair and to clean wounds. Because it readily decomposes in the presence of light, heat, or metallic catalysts into water and oxygen, the quantity of a hydrogen peroxide solution must be checked regularly to maintain its effectiveness. The concentration of hydrogen peroxide can be analyzed by redox titration with potassium permanganate. Titration is a method of volumetric analysis-the use of volume measurements to analyze the concentration of an unknown. The most common types of titrations are acid-base titrations, in which a solution of an acid, for example, is analyzed by measuring the amount of a standard base solution required to neutralize a known amount of the acid. A similar principle applies to redox titrations. If a solution contains a substance that can be oxidized, then the concentration of that substance can be analyzed by titrating it with a standard solution of a strong oxidizing agent.

Chem 106 L

Lab Final

Background 2 of 2

Oxidation-reduction (redox) reactions involve a transfer of electrons between the species being oxidized and the species being reduced. The reactions are often balanced by separating the reaction components into half-reactions: oxidation (loss of electrons) and reduction (gain of electrons). In a redox reaction, the number of electrons lost by a species being oxidized is always equal to the number of electrons gained by the species being reduced. In the reaction being studied in this lab, solutions of hydrogen peroxide, H2O2, and potassium permanganate, KMnO4, will be combined in acidic solution. KMnO4, will be used as the titrant to analyze the concentration of hydrogen peroxide in a drugstore bottle. The KMnO4 solution is purple in color, as it is added to the hydrogen peroxide solution, it reacts with the H₂O₂ to produce colorless Mn²⁺ , and thus the color will fade in the flask. When all the H₂O₂ has been used up, the last drop of potassium permanganate that is added will keep its color. The endpoint of the titration is the point at which the last drop of KMnO4 added to the solution causes it to turn pink.

Subject | Subject

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Safety

• H₂SO₄ is severely corrosive to eyes, skin, and other body tissues. Always add acid to water, never the reverse.

• KMnO₄ is a skin and eye irritant and a strong stain; it will stain skin and clothing. Goggles (and aprons if you choose) should be worn at all times. If solutions are spilled on skin, wash those areas immediately with copious amounts of water.

• Report all spills to the teacher. Wash hands thoroughly with soap and water after completion of the lab.

Subject | Subject

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Procedure​

• 1. Clean the buret as instructed.

• 2. Fill buret with KMnO4. Be sure to get rid of any air bubbles by opening the stopcock. Discard into waste container. Volume of KMnO4 needs to be below zero mark on buret before starting titration.

• 3. Record the initial volume of KMnO4 to the correct number of significant figures.

• 4. Place 1.00 mL of the hydrogen peroxide solution into a 125-250 mL Erlenmeyer flask. (we will use a micropippette)

• 5. Add about 25 mL of distilled water to the flask.

Subject | Subject

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Procedure​

• ​6. Place 5.0 mL of 6 M H₂SO₄ into the flask.

• 7. Swirl the contents of the flask.

• 8. Titrate the hydrogen peroxide solution with the KnMnO4 solution. Record the final volume of KMnO4.

• 9. Place the contents of the flask into the waste beaker and rinse the flask.

• 10. Repeat Steps 2-8 two more times. You should conduct three trials total.

  • Receive a stamp for your first quality titration (correct end point)

• 11. Clean buret as instructed. Wash all other used glassware.

• 12. Wipe lab bench with rag.

• 13. Wash your hands with plenty of soap and water

Chem 106 L

Lab Final

Data Table

0.02M

Pre-lab questions​

1. What is a titrant? What is the titrant in this lab?

2. What is an analyte? What is the analyte in this lab?

3. Balance the following redox reaction in acidic solution.
(Show your work; the following slides will guide/work through it)

• MnO₄ ^‒ _(aq) + H₂O_2(aq) --> Mn²⁺_(aq) + O_2(g)

a. How many electrons are transferred in this reaction?

b. What species is being oxidized? What species is being reduced?

Chem 106 L

Lab Final

Labelling

Drag the oxidation numbers over the element.

(include this in your learning log)

Drag labels to their correct position on the image

0

-2

+5

+8

+2

-1

+7

+1

Multiple Choice

Why is Oxygen's oxidation number in H2O2

"-1"

• because it is a peroxide

• Because it is a diatomic

• because oxygen is always -1

Labelling

Drag and drop the half reactions

Drag labels to their correct position on the image

Multiple Choice

Are the non- hydrogen and non-oxygens balanced?

• Yes

• No- we need to add a coefficient.

Labelling

balance the oxygens

Drag labels to their correct position on the image

4O

2O₂

Empty

Labelling

balance the hydrogens

Drag labels to their correct position on the image

8H

Empty

4H

Labelling

balance the charge

Drag labels to their correct position on the image

empty

5e-

2e-

6e-

7e-

Dropdown

Balance the half reaction below;

add items to the correct side left to right.

One blank may be filled with "empty"​

​ ​ ​

Select answer

+ H₂O_2(aq) -->O_2(g) +​

Select answer

+​

Select answer

Multiple Choice

based on the balanced half reactions;

How many electrons will be transferred in the final balanced equation

• 2 e-

• 10 e-

• 7e-

• 20 e-

• 3e-

Set up post lab Calculation

Example of Setting up Calculations (using the vinegar titration lab)
*** THIS IS JUST an example and is using the reaction from the Vinegar Titration

Determine moles of HC2H3O2 (this is the solute in the acid solution)

• Because the ratio of NaOH to HC2H3O2 is 1:1 based on the chem.rxn., 

(VNaOH in liters) x (Molarity NaOH) = moles NaOH= moles of HC2H3O2.  

(Final - Initial)/1000   x (                M) = _____ moles of HC2H3O2.

Determine grams of HC2H3O2 solute in the vinegar

• Grams of HC2H3O2 = moles of HC2H3O2 x Molar Mass of HC2H3O2.  

   =  _______________ * 62.05 g/mol

 

Determine  grams of vinegar solution

• calculated from the volume of vinegar titrated x density vinegar. (assume density of all vinegars = 1.005 g/mL)

  • _____ ml * 1.005 g/ml =      _________ grams vinegar

The next 2 slides have the post lab calculations.
Write out (summarize) each of the post lab questions and set-up the calculation for at least 3 of the post lab calculations
--> see the examples to the right

Post Lab Questions​ 1 of 2 Must be set-up prior to turning in pre-lab

1. Calculate the average volume, in milliliters, of KMnO4 used to titrate 1.00 mL of hydrogen peroxide solution. Convert to liters

2. Using the average volume of KMnO₄ and the molarity of KMnO4, determine the moles of KMnO₄ used to titrate 1.00 mL of hydrogen peroxide solution.

3. Calculate the moles of H₂O₂ that were present in 1.00 mL of hydrogen peroxide solution. (hint... mole ratio)

4. Calculate the grams of H₂O₂ that were present in 1.00 mL of hydrogen peroxide solution.

Chem 106 L

Lab Final

Post Lab questions​ 2 of 2
At least 3 Must be set-up prior to turning in pre-lab, but all must have a spot saved.

5. Assume the density of the H₂O₂ solution to be 1.00 g/mL, calculate the percentage of H₂O₂ in solution. % = (mass of H₂O₂ /H₂O₂ solution) *100
6. The accepted percentage of hydrogen peroxide in solution is 3.00%. Calculate the percent error.

Chem 106 L

Lab Final

​Optional:

​

Video goes over some of the concepts for this lab​

Hotspot

Click where the potassium permanganate is located

Hotspot

Click where the hydrogen peroxide is located