CBSE Class 12 chemistry practical, Electrochemistry · Physical chemistry experiments

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

Concentration cell: cell potential and Nernst equation (Class 12 chemistry practical)

You measure emf of a galvanic cell when zinc and copper ion concentrations differ from standard values.

Concentrations and cell diagram follow your manual — substitute into Nernst with your measured emf only.

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.

Copper(II) sulphate solutions are harmful if swallowed and irritate skin and eyes.
Zinc and copper electrodes may have sharp edges — handle carefully.
Do not short the cell with wet hands across both electrodes.

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 construct a concentration cell based on the Zn²⁺/Zn and Cu²⁺/Cu couples and verify how cell potential changes with concentration using the Nernst equation.

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

Apparatus and chemicals

Apparatus and chemicals
Item	Note
Voltaic cell assembly or beakers with salt bridge	Porcelain or KNO₃ agar bridge as supplied.
Zinc and copper electrodes	Clean with emery paper as directed.
Digital voltmeter / potentiometer (if school has one)	Connect with correct polarity.
Measuring cylinders / pipettes	For preparing dilute ion solutions.
Zinc sulphate solution (ZnSO4)	Use the concentration, mass, and volume values printed in your school laboratory manual. This page does not invent a numerical result for you.
Copper sulphate solution (CuSO4)	Different concentration from Zn side if manual sets up concentration cell.
Salt bridge electrolyte (KNO3)	As provided — do not invent bridge composition.
Distilled water (H2O)	For dilutions in manual.

Theory and reaction

Open

Cell emf depends on concentrations via the Nernst equation: E = E° − (RT/nF) ln Q at equilibrium approaches zero.

For a Daniell cell, increasing Cu²⁺ or decreasing Zn²⁺ typically increases emf until concentrations equilibrate.

Salt bridge maintains electrical neutrality between half-cells.

Zinc reduces copper ion; Nernst equation links E to reaction quotient Q.

Picture guide

Metal strip in a coloured salt solution in a beaker — A more reactive metal can displace another from solution. Watch colour change and any coating on the strip — write what you actually see.

Procedure

Prepare ZnSO₄ and CuSO₄ solutions at the molarities your manual lists.
Immerse Zn in Zn²⁺ and Cu in Cu²⁺. Connect salt bridge.
Connect voltmeter: note which electrode is positive (cathode).
Record emf. Change one concentration as manual directs and record new emf.
Calculate Q for each setup and compare experimental E with Nernst prediction using E° values your manual supplies.

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

S. No.	[Zn²⁺] (mol L⁻¹)	[Cu²⁺] (mol L⁻¹)	Cell emf measured (V)
1
2
3

Calculation

Use Nernst: E = E° − (0.0591/2) log([Zn²⁺]/[Cu²⁺]) at 25 °C if that is the cell form your manual uses. Compare % difference — do not fabricate emf readings.

Result

Report measured emf for each concentration pair and state whether Nernst equation agreement is satisfactory.

Precautions

Clean electrode surfaces before each setup.
Salt bridge must contact both solutions.
Do not short the cell with wet hands on both electrodes.

Viva questions

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

Question 1 of 4

In a galvanic cell, oxidation occurs at the…

A. CathodeB. AnodeC. Salt bridge onlyD. Voltmeter

Pick an answer first.

Show all questions and answers

In a galvanic cell, oxidation occurs at the…
Answer: Anode. Reason: Anode is where oxidation happens (electrons leave).
The Nernst equation shows emf…
Answer: Varies with reaction quotient Q. Reason: Concentration changes shift Q and thus E.
Purpose of the salt bridge is to…
Answer: Complete the circuit and minimise liquid junction potential. Reason: It allows ion flow while keeping half-cells separate.
When E_cell = 0, the cell is at…
Answer: Electrochemical equilibrium. Reason: No driving force for net reaction — equilibrium.

Common mistakes

Reversing voltmeter leads and reporting negative emf without interpretation.
Using activities as concentrations without manual permission.
Omitting salt bridge — large junction potential errors.

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.

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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