Here is the NCERT Class 12 Chemistry-based explanation for the Measurement of Electrode Potential:
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📘 Measurement of Electrode Potential (Class 12 – Chapter: Electrochemistry)
🔹 What is being measured?
The electrode potential of a half-cell cannot be measured directly. Instead, it is always measured relatively by comparing it to a reference electrode, which is the:
> ✅ Standard Hydrogen Electrode (SHE), assigned a value of 0.00 V.
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🔹 Standard Hydrogen Electrode (SHE)
Components:
Platinum electrode coated with platinum black
Dipped in 1 M HCl (H⁺ ions)
Hydrogen gas at 1 atm pressure is bubbled over it
Half-cell Reaction:
\text{2H}^+(aq) + 2e^- \rightleftharpoons \text{H}_2(g)
SHE serves as the reference electrode for measuring other electrodes.
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🔹 Measurement Process (NCERT Style):
1. Set up a galvanic cell by connecting the unknown electrode (whose potential you want to measure) with SHE.
2. Measure the EMF (electromotive force) of the cell using a voltmeter.
3. Connect the positive terminal of the voltmeter to the cathode.
4. Determine the electrode potential of the unknown electrode using:
E_{\text{cell}} = E^\circ_{\text{right}} - E^\circ_{\text{left}}
E_{\text{cell}} = E^\circ_{\text{unknown electrode}} - 0.00
\Rightarrow E^\circ_{\text{unknown}} = E_{\text{cell}}
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🔹 Example:
If you connect a zinc electrode (Zn/Zn²⁺) with SHE:
The voltmeter reads –0.76 V
That means the zinc electrode is more negative than SHE
Therefore, E°(Zn²⁺/Zn) = –0.76 V
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🔹 Diagram (from NCERT):
A simple electrochemical cell with:
One side: SHE
Other side: Metal electrode (e.g., Zn)
Salt bridge
Voltmeter showing EMF
(You can find this figure in NCERT Chemistry Class 12 Chapter 3)
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🔹 Summary Points (as per NCERT):
Electrode potentials are relative values, not absolute
SHE is the universal reference electrode
Standard electrode potentials are measured under standard conditions
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Would you like a labeled diagram or explanation of how to construct the galvanic cell for measurement?
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