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CBSE Class 12 chemistry practical · Volumetric analysis

Source: CBSE Class 12 chemistry practical syllabus · use your school laboratory manual (NCERT Lab Manual where your school uses it).

Titration of KMnO4 with Mohr’s salt (Class 12 chemistry practical)

You standardise or find the strength of KMnO₄ using Mohr’s salt as the reducing agent.

Record your own concordant readings. Strengths and worked numbers come from your manual and your titres.

Published practice page. Concentrations, masses, and numerical answers come from your school laboratory manual and your own readings — not invented here. Not yet reviewed by a named chemistry reviewer. Version 1.0.0, updated 2026-10-03.

Safety — read before you start

Safety warning. Practise here. Perform the real experiment only in your school lab, with your teacher present.

  • Dilute sulphuric acid is corrosive.
  • Iron(II) solutions can irritate; follow your teacher’s handling rules.
  • KMnO₄ is an oxidiser and stains.

Wear: Lab coat, Splash goggles, Gloves, as your teacher directs.

Follow your teacher’s disposal instructions. Do not pour leftovers down a household drain.

Loads only after you tap. Use the lab hands to pick up and use equipment (pointer hidden in the scene). Falls back to a flat diagram if WebGL is unavailable.

Aim

To determine the strength (molarity) of a potassium permanganate solution by titrating it against a standard Mohr’s salt solution, using the values in your laboratory manual.

Methods and quantities can differ between schools. Follow your teacher's instructions.

Apparatus and chemicals

Apparatus and chemicals
ItemNote
Burette and standFor KMnO₄ solution.
Pipette and fillerFor Mohr’s salt solution. Do not pipette by mouth.
Conical flaskRinse with distilled water only.
White tileHelps you see the pale pink end point.
Wash bottleDistilled water.
Potassium permanganate solution (KMnO4)In the burette. Use the concentration, mass, and volume values printed in your school laboratory manual. This page does not invent a numerical result for you.
Mohr’s salt solution ((NH4)2Fe(SO4)2·6H2O)Standard ferrous ammonium sulphate solution from your manual. Use the concentration, mass, and volume values printed in your school laboratory manual. This page does not invent a numerical result for you.
Dilute sulphuric acid (H2SO4)Keeps the medium acidic. Volume as in your manual. Do not use HCl or HNO₃.
Burette and conical flask set up for titration
Read the burette at eye level. The end-point colour in a diagram is only a guide — your titre is the volume you measure.

Theory and reaction

Open

In acid medium, MnO4- oxidises Fe2+ to Fe3+. Permanganate is reduced to almost colourless Mn2+.

Mohr’s salt provides Fe2+ and is more stable than simple ferrous sulphate for school work when prepared as directed.

No external indicator is needed. The end point is the first lasting pale pink from a slight excess of KMnO4.

Mole ratio from the balanced equation: 1 mol MnO4- reacts with 5 mol Fe2+.

MnO4- + 5 Fe2+ + 8 H+ gives Mn2+ + 5 Fe3+ + 4 H2O

Procedure

  1. Rinse and fill the burette with KMnO₄. Remove air bubbles. Note the initial reading.
  2. Pipette the Mohr’s salt volume your manual states into a clean conical flask.
  3. Add dilute sulphuric acid as your manual directs.Safety: Dilute sulphuric acid is corrosive.
  4. Titrate with KMnO₄ while swirling until the first pale pink that persists.
  5. Record final reading. Repeat for concordant titres.

Observation table

Enter the readings from your school lab in the practical file below. This page does not fill them in for you.

Type the readings in your practical file

Calculation

Use MnO₄⁻ : Fe²⁺ = 1 : 5, the Mohr’s salt concentration and pipette volume from your manual, and your concordant titre. Write the molarity of KMnO₄ with units.

Result

State the molarity (or strength) of KMnO₄ you obtain from your own concordant readings.

Precautions

  • Keep the medium acidic with dilute H₂SO₄ as directed — not HCl or HNO₃.
  • Rinse the burette with KMnO₄ and the pipette with Mohr’s salt.
  • Do not rinse the conical flask with Mohr’s salt after pipetting.
  • Stop at lasting pale pink, not deep purple.

Viva questions

Answer one question at a time. The full answers stay closed until you open them.

Question 1 of 4

What is Mohr’s salt chemically?

Answer choices

Pick an answer first.

Show all questions and answers

  1. What is Mohr’s salt chemically?

    Answer: Ferrous ammonium sulphate hexahydrate. Reason: Mohr’s salt is (NH₄)₂Fe(SO₄)₂·6H₂O.

  2. MnO₄⁻ : Fe²⁺ mole ratio in acid medium is…

    Answer: 1 : 5. Reason: One permanganate oxidises five Fe²⁺ ions.

  3. Why is no external indicator used?

    Answer: KMnO₄ is self-indicating (pale pink at end point). Reason: Excess KMnO₄ gives a lasting pale pink.

  4. Which acid medium is preferred?

    Answer: Dilute H₂SO₄. Reason: Dilute sulphuric acid is the usual medium for this school titration.

Common mistakes

  • Using HCl (can be oxidised by KMnO₄) or HNO₃ (oxidising acid).
  • Adding a separate indicator.
  • Confusing the 1:5 Fe²⁺ ratio with the 2:5 oxalate ratio.

Frequently asked questions

Can I do this at home?
No. Use this page to practise the order of steps and viva. Do the real experiment only in your school laboratory, with your teacher present.
Is this the same calculation as the oxalic acid titration?
No. The balanced mole ratio is different (1:5 with Fe²⁺ vs 2:5 with oxalate). Always use the equation for the reducing agent you used.

Your practical file

Name, school, and roll number are optional and are not sent anywhere.

The practical file opens on this device.

Review

Not yet reviewed by a named chemistry reviewer. Published for practice only — follow your teacher and laboratory manual for quantities and safety.

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