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chemistry for easy study, Study notes of Chemistry

Chemistry

chemistry for esy study to be done

Typology: Study notes

2021/2022

Uploaded on 09/09/2025

sriraman
sriraman 🇺🇸

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AP Lab #12 – Redox Titration
Potassium permanganate has been widely used as an oxidizing agent for over 100 years.
It is a reagent that is readily available, inexpensive, and requires no indicator unless very dilute
solutions are used. One drop of 0.01 M permanganate imparts a perceptible pink color to the
volume of solution normally used in a titration. This color is used to indicate excess of the
reagent. Permanganate undergoes a variety of chemical reactions, since manganese can exist in
oxidation states of +2, +3, +4, +6, and +7.
When sodium bisulfite reacts with permanganate ion in acidic solution, the bisulfite gets oxidized
into bisulfate:
H2O + HSO3- HSO4- + 2H+ + 2e-
For every 1 mole of bisulfite, two moles of electrons are transferred. Bisulfite can be easily
oxidized by the potassium permanganate because the permanganate ions will undergo reduction
to gain electrons and thereby change their oxidation state from +7 to a smaller charge.
In this lab, you will do a redox titration in order to calculate the new charge of the
manganese ion product. Permanganate ions are purple because manganese is a transition metal,
and transition metals form colored solutions. However, after you titrate with permanganate, the
manganese will change color due to a different oxidation state.
Science Practices: [2.B, 3.A, 5.B, 5.C, 5.E, 5.F, 6.G]
Objectives
How can we determine the oxidation state of manganese in a redox titration?
Safety
Wear protective glasses at all times. Wear gloves and an apron when working with
potassium permanganate. CAUTION: Potassium permanganate. is a strong oxidizing agent.
Do NOT pour potassium permanganate down the sink. Rinse all potassium permanganate into a
waste container, including your burette rinse.
Materials
0.01M KMnO4 (Exact concentration of permanganate will be given to you by instructor)
0.10 M NaHSO3Distilled water
1.00 M H2SO4Ring Stand Burette Clamp
stir rod Wash bottle Burettes 50 mL
Safety glasses Apron Disposable pipettes
Stir plate Gloves Funnel
125 mL Erlenmeyer flask Stir bar 100 mL graduated cylinder
balance small weighing boat Large waste beaker
Procedure
54
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AP Lab #12 – Redox Titration

Potassium permanganate has been widely used as an oxidizing agent for over 100 years. It is a reagent that is readily available, inexpensive, and requires no indicator unless very dilute solutions are used. One drop of 0.01 M permanganate imparts a perceptible pink color to the volume of solution normally used in a titration. This color is used to indicate excess of the reagent. Permanganate undergoes a variety of chemical reactions, since manganese can exist in oxidation states of +2, +3, +4, +6, and +7. When sodium bisulfite reacts with permanganate ion in acidic solution, the bisulfite gets oxidized into bisulfate:

H 2 O + HSO 3 -^ HSO 4 -^ + 2H+^ + 2e-

For every 1 mole of bisulfite, two moles of electrons are transferred. Bisulfite can be easily oxidized by the potassium permanganate because the permanganate ions will undergo reduction to gain electrons and thereby change their oxidation state from +7 to a smaller charge. In this lab, you will do a redox titration in order to calculate the new charge of the manganese ion product. Permanganate ions are purple because manganese is a transition metal, and transition metals form colored solutions. However, after you titrate with permanganate, the manganese will change color due to a different oxidation state. Science Practices: [2.B, 3.A, 5.B, 5.C, 5.E, 5.F, 6.G]

Objectives

How can we determine the oxidation state of manganese in a redox titration?

Safety

Wear protective glasses at all times. Wear gloves and an apron when working with potassium permanganate. CAUTION: Potassium permanganate. is a strong oxidizing agent. Do NOT pour potassium permanganate down the sink. Rinse all potassium permanganate into a waste container, including your burette rinse.

Materials

0.01M KMnO 4 (Exact concentration of permanganate will be given to you by instructor) 0.10 M NaHSO 3 Distilled water 1.00 M H 2 SO 4 Ring Stand Burette Clamp stir rod Wash bottle Burettes 50 mL Safety glasses Apron Disposable pipettes Stir plate Gloves Funnel 125 mL Erlenmeyer flask Stir bar 100 mL graduated cylinder balance small weighing boat Large waste beaker

Procedure

Design an experimental procedure that will determine the oxidation state of manganese at the end of each titration with your solution of 10 mL of 0.10 M NaHSO3. You must do at least three titrations for accuracy and take an average. Each titration requires that the NaHSO 3 be in acidic solution. Use no more than 2.00 mL of 1.00 M H 2 SO 4 for each 10 mL sample of 0.10 M NaHSO 3. You may need to add more water to cover the stir bar. Show your proposed procedure to your teacher before attempting the experiment yourself.

Observations (at least 5)

Data: Redox Titration Data

Create your own data table from the procedure you have designed. Make sure to include a title for this table.

Calculations

Show all of your work.

1. Using the molarity of potassium permanganate solution and your titration data, calculate the moles of permanganate ion used in each trial. 2. Using the molarity and volume of NaHSO 3 used, calculate the moles of HSO 3 -^ ions for each trial. 3. Using the stoichiometric ratio of the oxidation half-reaction in the introduction, calculate the moles of electrons transferred from the HSO 3 -^ ions in each trial. 4. Calculate the ratio of the moles of electrons transferred/moles of permanganate ion for each trial. Take an average of all three trials and round the moles of electrons transferred per moles of permanganate ion to the nearest whole number. 5. Using calculation #4 and knowing that the manganese in permanganate has an oxidation state of +7, calculate the charge of the manganese ion in the final product. 6. Write the reduction half-reaction for permanganate ion in acidic solution. 7. Write the balanced net ionic equation for the reaction of permanganate and bisulfite in acidic solution.

Discussion

 Answer the objective.  Show the balanced net ionic equation for the reaction you did.  Summarize your results.  How accurate and reproducible were they?

Additional Discussion Questions

1. Define the words titrant and analyte. 2. Show the dissociation of sodium bisulfite. 3. Why was there no need for an additional indicator in this lab?