Define electrochemical series and what are its application
Answers
Answer:
Electrochemical Series:
A series of electrodes or half cells arranged in order of their increasing standard oxidation potentials or in the decreasing order of their standard reduction potentials is called as electromotive force series or electrochemical series.
Electrochemical series is also known as e.m.f. series
Characteristics Electrochemical Series :
In this series, all reduction potentials are given on hydrogen scale whose Eo is taken as zero.
The standard reduction potential of an element is a measure of the tendency of that element to get reduced.
The element which has greater reduction potential gets reduced easily. While the elements with low reduction potential will get easily oxidized
Elements that lose electron more easily have lower (negative) reduction potential and those which lose electrons with greater difficulty or instead of losing they accept electrons more easily have a higher (positive) reduction potential.
In EMF series elements having higher (+ ve), reduction potential is placed at the top. While those having lower (-ve) reduction potential are placed at the bottom. SHE has the middle position in the electrochemical series.
The substances which are stronger reducing agents than hydrogen are placed below the hydrogen in the series and have negative standard reduction potential. The substances which are weaker reducing agents than hydrogen are placed above the hydrogen in the series and have positive standard reduction potential. Thus as we move down the group strength of reducing agent increases while the strength of oxidizing agent decreases.
Metal at the bottom is the most active metal. As we move down in the series activity and electropositivity of metals increase. Nonmetal at the Top is the most active nonmetal. As we move down in the series activity and electronegativity of nonmetal decreases.
Applications of Electrochemical Series:
For Choosing Elements as Oxidising Agents:
The elements which have more electron accepting tendency are oxidizing agents.
Elements at the top of the electrochemical series have higher (+ ve) reduction potential. Hence they gain an electron from other elements and oxidize them. So they are good oxidizing agents.
Element (F2) at the topmost position of electrochemical series which has highest reduction potential is the strongest oxidizing agent.
Oxidising power decreases from top to bottom in the series.
e.g. The elements like Cu, Ag, Hg, Br2, Cl2 etc. are good oxidizing agents. F2 is the strongest oxidizing agent.
For Choosing Elements as Reducing Agents:
The elements which have more electron losing tendency are reducing agents.
The elements at the bottom in electrochemical series have lower (- ve) reduction potential. Hence they lose electrons readily and supply to other element and reduce them.
So bottom elements in electrochemical series are reducing agent. Reducing strength goes on increasing from top to bottom in the series.
Element (Li) having bottom-most position has lowest reduction potential hence it is the strongest reducing agent.
e.g. The element like Zn, Cd, Ni, K etc. are good reducing agents.
For Studying displacement reaction:
One metal can be displaced from salt solution by another metal is known as a redox reaction. Elements having higher reduction potential will gain electrons and that having lower reduction potential will lose electrons. Hence element lower in electrochemical series can displace an element placed higher in electrochemical series from its salt solution.
Example-1: Zn displaces Cu from CuSO4, because, zinc is placed lower in electrochemical series and has lower reduction potential while Cu is placed higher in electrochemical series and has higher reduction potential. Hence zinc can easily displace copper from CuSO4
Zn + CuSO4 → ZnSO4 + Cu i.e.
Zn + Cu++(aq) → Zn ++(aq) + Cu