Electrochemical Series or Reactivity Series, is a list of metals and semi-metals ranked in order of their standard electrode potential or standard reduction potential. In the electrochemical series, metals and other substances are arranged in decreasing order of their tendency to gain electrons (reduce) or lose electrons (oxidize). Electrochemical Series is based on the measurements of the potential of various electrodes in comparison to the standard hydrogen electrode (SHE).
In this article, we will discuss the concept of the Electrochemical Series in detail including its definition, chart, as well as tricks to remember the Electrochemical Series.
Table of Content
What is an Electrochemical Series?
The electrochemical series organizes electrodes (metals and non-metals) in contact with their ions based on their standard reduction or oxidation potentials. The standard electrode potential is determined by measuring the voltage when the half-cell is connected to the standard hydrogen electrode under standard conditions.
Electrochemical Series Definition
Electrochemical Series is defined as the arrangement of the electrode with the electrode half-reaction in order of decreasing standard potential.
Electropositive and Electronegative Elements
Generally speaking, elements that are more likely to lose electrons to their solution are referred to as electropositive. Conversely, elements that pick up electrons quickly are referred to as electronegative. In the series, these are usually located below hydrogen.
The electrochemical series can help us understand the order in which metals can replace each other in their salts. Usually, electropositive metals can replace hydrogen from acids.
Electrochemical Series Chart
The electrochemical series chart is a simple way of visualizing similar vs dissimilar metals. The elements which are placed closer to each other, tend to display similar properties while those that are far apart have various dissimilarities.
|
Element |
Electrode Reaction (Reduction) |
Standard Electrode Reduction Potential E° (in volt) |
|---|---|---|
|
Li |
Li+ + e– → Li |
-3.05 |
|
K |
K+ + e– → K |
-2.925 |
|
Ca |
Ca2+ + 2e– → Ca |
-2.87 |
|
Na |
Na+ + e– → Na |
-2.714 |
|
Mg |
Mg2+ + 2e– → Mg |
-2.37 |
|
Al |
Al3+ + 3e– → Al |
-1.66 |
|
Zn |
Zn2+ + 2e– → Zn |
-0.7628 |
|
Cr |
Cr3+ + 3e– → Cr |
-0.74 |
|
Fe |
Fe2+ + 2e– → Fe |
-0.44 |
|
Cd |
Cd2+ + 2e– → Cd |
-0.403 |
|
Ni |
Ni+ + 2e– → Ni |
-0.25 |
|
Sn |
Sn2+ + 2e– → Sn |
-0.14 |
|
H2 |
2H+ + 2e– → H2 |
0.00 (Standard) |
|
Cu |
Cu2+ + 2e– → Cu |
+0.337 |
|
I2 |
I2 + 2e– → 2I– |
+0.535 |
|
Ag |
Ag+ + e– → Ag |
+0.799 |
|
Hg |
Hg2+ + 2e– → Hg |
+0.885 |
|
Br2 |
Br2 + 2e– → 2Br– |
+1.08 |
|
Cl2 |
Cl2 + 2e– → 2Cl– |
+1.36 |
|
Au |
Au3+ + 3e– → Au |
+1.50 |
|
F2 |
F2 + 2e– → 2F– |
+2.87 |
Note:
- The negative sign of standard reduction potential indicates that an electrode when joined with SHE acts as an anode and oxidation occurs on this electrode.
- Similarly, the +ve sign of standard reduction potential indicates that the electrode when joined with SHE acts as a cathode and reduction occurs on this electrode.
Trick to Remember Electrochemical Series
One basic idea in electrochemistry is the electrochemical series, which gives different metals and their relative propensities to undergo oxidation or reduction reactions a systematic order. This series is a useful tool for determining which way electrons will flow in various redox reactions. Mnemonic to learn electrochemical series is discussed in the later part of the article.
Electrochemical Series Mnemonic
To remember the order of elements in the electrochemical series, use the mnemonic
Like Kareena Can Not Memorize All Zoology Important Concepts, No student Has Complete Information in Silver Mercury Because Chemistry Over Flows.
Each capital letter represents the symbol of an element in the series:
- Like-Li-Lithium
- Kareena-K-potassium
- Can-Ca-Calcium
- Not-Na-Sodium
- Memorize-Mg-Magnesium
- All-Al-Aluminum
- Zoology-Zn-Zinc
- Important-Fe-Iron
- Concepts-Co-Cobalt
- No-Ni-Nickel
- Student-Sn-Tin
- Has-H-Hydrogen
- Complete-Cu-Copper
- Information-I-Iodine
- Silver-Ag
- Mercury-Hg
- Because-Br-Bromine
- Chemistry-Cl-Chlorine
- Over-O-Oxygen
- Flows-F-Flourine
Characteristics of Electrochemical Series
Key characteristics of Electrochemical Series are:
- The substances that are stronger reducing agents than hydrogen are placed above hydrogen in the series and have negative values of standard reduction potentials.
- All those substances that have positive values of reduction potentials and placed below hydrogen in the series are weaker reducing agents than hydrogen.
- The substances which are stronger oxidizing agents than H+ ions are placed below hydrogen in the series.
- The metals on the top (having high negative values of standard reduction potentials) tend to lose electrons readily. These are active metals.
- The non-metals on the bottom (having high positive values of standard reduction potentials), tend to accept electrons readily. These are active non-metals.
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Applications of Electrochemical Series
Some of the common applications of Electrochemical Series are:
Electropositive Character of Metals
The electropositive character also depends on the tendency to lose electrons or electrons. Like reactivity, the electropositive character of metals decreases from top to bottom in the electrochemical series. Based on standard reduction potential values, metals are divided into three groups:
- Strongly electropositive metals: Metals having standard reduction potential near about -2.0 volt or more negative like alkali metals, alkaline earth metals are strongly electropositive.
- Moderately electropositive metals: Metals having values of reduction potentials between 0.0 and about -2.0 volt are moderately electropositive. Al, Zn, Fe, Ni, Co, etc., belong to this group.
- Weakly electropositive metals: The metals that are below hydrogen and possess positive values of reduction potentials are weakly electropositive. Cu, Hg, Ag, etc., belong to this group.
Reactivity of Metals
The activity of the metal depends on its tendency to lose electrons or electrons, i.e., the tendency to form a cation. This tendency depends on the magnitude of standard reduction potential. The metal with a high negative value (or smaller positive value) of standard reduction potential readily loses the electron or electrons and is converted into a cation. Such a metal is said to be chemically active.
Reducing Power of Metals
Reducing nature depends on the tendency of losing electron or electrons. More the negative reduction potential, more is the tendency to lose electron or electrons. Thus, reducing nature decreases from top to bottom in the electrochemical series. The power of the reducing agent increases as the standard reduction potential becomes more and more negative.
Oxidizing Nature of Nonmetals
Oxidizing nature depends on the tendency to accept electron or electrons. More the value of reduction potential, higher is the tendency to accept electron or electrons. Thus, oxidising nature increases from top to bottom in the electrochemical series. The strength of an oxidising agent increases as the value of reduction potential becomes more and more positive.
Calculation of Standard emf (E0) of Electrochemical Cell
The standard emf of the cell is the sum of the standard reduction potential of the two half cell: reduction half cell and oxidation half cell
E0cell = E0red + E0ox
By convention, the standard oxidation potential is always expressed in terms of reduction potential.
Thus, standard oxidation potential (E0ox) = – standard reduction potential (E0red)
Therefore, E0cell = ( standard reduction potential of reduction half cell) – ( standard reduction potential of oxidation half cell)
As oxidation takes place at anode and reduction takes place at the cathode. Hence,
E0cell = E0cathode – E0anode
Electrochemical Series: Conclusion
Electrochemical Series is the arrangement of elements in the increasing or decreasing order of their standard electrode potential. We have discussed the concept in details in this article, also we have learned the trick to learn this table.
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Electrochemical Series: FAQs
1. Define Electrochemical Series.
An electrochemical series is a series in which elements are arranged in an increasing or decreasing order of their standard electrode potential.
2. What is the Best Reducing Agent in the Electrochemical Series?
The best reducing agent in the electrochemical series is the species with a higher position in the series, like lithium or cesium, as they readily undergo oxidation by losing electrons
3. What is Electrochemical Series of Metals?
The electrochemical series of metals is a list that ranks metals based on their tendency to undergo oxidation (lose electrons) in aqueous solutions.
4. What is the Arrangement of Elements in the Electrochemical Series?
The arrangement of elements in the electrochemical series is based on their standard electrode potentials. It ranks elements from the most reactive (strongest reducing agents) to the least reactive (strongest oxidizing agents).
5. How do you Remember Electrochemical Series?
To remember the electrochemical series you can use the following Mnemonic:
Like Kareena Can Not Memorize All Zoology Important Concepts, No student Has Complete Information in Silver Mercury Because Chemistry Over Flows.
6. How do you Make an Electrochemical Series?
Create an electrochemical series by listing elements, arranging them based on standard electrode potentials, and observing trends.
7. What is Electrode Potential Value of a Standard Hydrogen Electrode?
0.0 V is the electrode potential value of a standard hydrogen electrode.
8. Why Electrochemical Series is Called the Activity Series?
It is called the activity series because it reflects the relative reactivity or activity of different elements.