Exams Prep Master
Anode and cathode are defined by the flow of current. The terms were coined in 1834 by William Whewell, who derived the words from the Greek word “Kathodes” which means ‘descent’ or ‘way down’. The anode is the negative or reducing electrode from where electrons are released to the external circuit and oxidize during an electrochemical reaction. The cathode is the positive or oxidizing electrode that acquires electrons from the external circuit.
| Table of Content |
Keyterms: Anode, cathode, electrode, Electron, Electrochemical cell, Galvanic cell, circuit, electrochemical reaction, electricity, Electrochemistry
What is Anode?
[Click Here for Sample Questions]
An anode is a place from where electricity passes through in a cell. It is a point where oxidation takes place. Anodes react and give off the electrons by which they can go into the driving circuit.
- If we take an electrochemical cell or a galvanic cell, we can see that anode is negative. In Anode, mostly electrons move towards the external part of the circuit. Such devices include secondary battery cells and diodes.
- If we take an electrolytic cell, we can see that it is positive. Such devices include primary battery cells, vacuum tubes, cathode ray tubes, and oscilloscopes.
Examples of Anode
- The anode is the negative terminal as it is where current flows into the cell in a discharging battery or galvanic cell. This inward current moving outwards is carried by electrons. The negative charge flowing in one direction is equal to the positive charge flowing in the opposite direction.
- The anode is the positive terminal that receives current from an external generator in a recharging battery. The current through a battery flows in an opposite direction of the current during discharge in the recharging battery.
- In a diode, the anode is the positive terminal where the current flows into the device. The electrode naming for diodes is based on the direction of the forward current.
Also read:
| Chapter Related Topics | ||
|---|---|---|
| Electrochemistry | Nernst Equation | Batteries |
| Fuel Cells | Corrosion | Daniell Cell |
| Difference Between Cell and Battery | Reduction Potential | Concentration Cell |
What is Cathode?
[Click Here for Previous Year Questions]
A cathode is a place from where electricity leaves through a cell. It is a point where reduction takes place. This is common in an electrochemical cell.
- Due to the decomposition of chemical compounds in the cell, the cathode results are negative in nature.
- If we take an electrochemical cell or a galvanic cell, we can see that cathode is positive. In this cell, electrical energy is generated due to chemical reactions taking place in it.
- It can be either a hot cathode or a cold cathode.
- Cold Cathodes are not heated with filament as it sends out more electrons than the generation of electrons in thermionic emission only.
- Hot Cathodes are heated with filament as it sends out electrons in thermionic emission.
Example of Cathode
The flow of electrons from the cathode interface to a species in solution is called the cathodic current.
Electrolytic Cell
It is in an electrolytic cell where the negative polarity is applied in the cathode. Some results of reduction at the cathode are pure metal or hydrogen gas from metal ions. On the other hand, by studying the relative reducing power of two redox agents, the couple for making the more reducing species is more cathodic with respect to the more easily reduced reagent.
Galvanic Cell
In a galvanic cell, the cathode is referred to as the positive pole. This positive pole is connected in order to allow the circuit to be completed. The anode of the galvanic cell gives off electrons and returns from the circuit into the cell through the cathode.
Electroplating Metal Cathode or Electrolysis
When metal ions form a pure metal surface on the cathode, they are reduced. Items to be plated with pure metal are attached and become part of the cathode in the solution.
Difference between Anode and Cathode
[Click Here for Sample Questions]
Following are the key differences between Anode and Cathode:
| Basis of Comparison | Anode | Cathode |
|---|---|---|
| Definition | It is an electrode where the electric current moves into. | It is an electrode where the electric current moves out. |
| Behavior | It attracts anions. | It attracts cations. |
| Nature | It is a source of the electric acceptor. | It is a source of electric donors. |
| Terminal polarity: electrolytic cell | It is positive in electrolytic cells. | It is negative in electrolytic cells. |
| Terminal polarity: galvanic cell | It is negative in galvanic cells. | It is positive in galvanic cells. |
| Reaction: electrolytic cell | Oxidation reaction occurs | A reduction reaction occurs. |
| Reaction: galvanic cell | It can become a cathode. | It can become anode. |
Charge on Cathode and Anode
[Click Here for Previous Year Questions]
In Cathode, there is a reduction response due to the following reasons:
- Electrons would be produced in the species of decreased ones.
- The Electrode lack electrons.
- Electrode gets charged positively.
In Anode, there is oxidation response due to the following reasons:
- Electrons would be reduced in the oxidized species.
- The electron would leave remain with an electron accumulation.
- Electrode gets charged negatively.
Why are Cathode Negative and Anode Positive?
[Click Here for Sample Questions]
Since the electrons were discovered, a cathode is defined as negative, and an anode is defined as positive. The cathode was derived from the Greek word- “kathodos”. This Greek word means “way down” in which current flowing from positive to negative leaves a device in which anode lets the current passes in. A cathode is not positive or negative always. In a discharging battery, it acts as positive whereas it acts negatively in another cell. The concept of Anode is the same as it can act positive or negative both, but nature will depend upon the type of cell.
Charges of a Voltaic Cell on Anode and Cathode
[Click Here for Previous Year Questions]
In a voltaic cell, the redox reactions can happen suddenly in both half-cells.
- In the cathode electrode, the reduction will take place creating positive charges in it.
- In the anode electrode, oxidation will take place creating negative charges in it.
Also Read:
Things to Remember
- The cathode is a negatively charged electrode.
- It attracts cations or positive charges and is the source of electrons or an electron donor.
- The anode is a positively charged electrode.
- The anode attracts electrons or anions and it may be a source of positive charge or an electron acceptor.
- The charge can flow either from positive to negative or from negative to positive.
- This is why an anode could be positively charged or negatively charged depending on the situation.
Previous Year Questions
- For hydrogen - oxygen fuel cell at one atm and 298K… [KCET 2019]
- For a cell reaction involving two electron changes… [KCET 2018]
- By passing electric current, NaClO3 is converted into NaClO4 according to the following equation… [KCET 2017]
- The quantity of electricity required to liberate 112cc of hydrogen at STP from acidified water is… [KCET 2001]
- At a particular temperature, the ratio of molar conductance to specific conductance of 0.01 M NaCl solution is… [KCET 2018]
- Which of the following is incorrect in a galvanic cell ?… [KCET 2016]
- The standard electrode potential is measured by… [KCET 2005]
- Impure copper containing Fe,Au,Ag as impurities is electrolytically refined. A current of 140A… [KCET 2014]
- For Cr2O−27+14H++6e−→2Cr+3+7H2O;E… [KCET 2014]
- Give: E0Mn+7|Mn+2 = 1.5 V and E0Mn+4|Mn+2 = 1.2 V, then E0Mn+7|Mn+4 is… [KCET 2019]
- An aqueous solution of CuSO4 is subjected to electrolysis using inert electrodes. The pH of the solution will… [KCET 2019]
- Zinc can be coated on iron to produce galvanized iron but the reverse is not possible. It is because… [NEET 2016]
Sample Questions
Ques: Are cations positive or negative? (1 mark)
Ans: A cation is a positively charged ion or an atom that has lost an electron.
Ques: What are the materials used for anode and cathode? (1 mark)
Ans: The materials that are used for anode and cathode are the metals like zinc and lithium.
Ques: How can we identify Anode and Cathode in a circuit? (1 mark)
Ans: We can see the direction of the electric current in the electric circuit. The path from where electricity passes is an anode and the path from where electricity moves out is a cathode.
Ques: In general, what are the signs of cathode and anode? (1 mark)
Ans: In general, a positive electrode can be defined as a cathode whereas a negative electrode can be defined as an anode.
Ques: Are the signs of cathode and anode is different in electrolytic and galvanic cells? (1 mark)
Ans: Yes, cathode is positive, and the anode is negative in galvanic cells. We can also state that the cathode is negative, and the anode is positive in electrolytic cells. Thus, signs of anode and cathode are different in both cells.
Ques: In corrosion, what is anode and cathode? (1 mark)
Ans: During the phase of corrosion, metal made of iron functions as anode in galvanic cells. It can oxidize to Fe2+ at the cathode electrode. Oxygen can decrease to water.
Ques: Is the cathode of LEDs positive or negative? (1 mark)
Ans: Cathodes are generally being labeled in LEDs. It should be linked to the driving voltage source’s floor. It should be on the adverse side. Also, the anode should be at the positive side.
Ques: What is the charge on anode and cathode? (2 marks)
Ans: In Cathode, there is a reduction response due to the following reasons:
- Electrons would be produced in the species of decreased ones.
- The Electrode lack electrons.
- Electrode gets charged positively.
In Anode, there is oxidation response due to the following reasons:
- Electrons would be reduced in the oxidized species.
- The electron would leave remain with an electron accumulation.
- Electrode gets charged negatively.
Ques: Differentiate between cathode and anode. (4 marks)
Ans: The difference between cathode and anode is given below:
| Basis of Comparison | Anode | Cathode |
|---|---|---|
| Definition | It is an electrode where the electric current moves into. | It is an electrode where the electric current moves out. |
| Behavior | It attracts anions. | It attracts cations. |
| Nature | It is a source of the electric acceptor. | It is a source of electric donors. |
| Terminal polarity: electrolytic cell | It is positive in electrolytic cells. | It is negative in electrolytic cells. |
Ques: Two half-reactions of an electrochemical cell are given below:
MnO–4 (aq) + 8H+ (aq) + 5e– → Mn2+ (aq) + 4H2O (I), E° = 1.51 V
Sn2+ (aq) → Sn4+ (aq) + 2e–, E° = + 0.15 V.
Write the redox reaction equation from the two half-reactions and calculate the cell potential from the standard potentials. Also, predict if the reaction is reactant or product favored. (All India 2010)
Ans: The reactions can be represented at the anode and at the cathode in the following ways:
At anode (oxidation):
Sn2+ → Sn4+ (aq) + 2e– ] × 5 E° = + 0.15 V
At cathode (reduction):
MnO-4(aq) + 8H+ (aq) + 5e- → Mn2+ (aq) + 4H2O (I)] × 2 E° = + 1.51 V
The Net R × M = 2MnO-4(aq) + 16H+ + 5Sn2+ → 2Mn2+ + 5Sn4+ + 8H2O
Now E°cell = E°cathode – E°anode
= 1.51 – 0.15 = + 1.36 V
∴ Positive value of E°cell favours formation of product.
Ques: a. Following reactions take place at cathode during the electrolysis of aqueous silver chloride solution:
Ag+(aq) + e- → Ag(s) E° = +0.80 V
H+(aq) + e- → ½ H2(g) E° = 0.00 V
Based on their standard reduction electrode potential (E°) values, which reaction is feasible at the cathode and why?
Define limiting molar conductivity. Why conductivity of an electrolyte solution decreases with the decrease in concentration? (Delhi 2015)
Ans: a. At the cathode Ag+ (aq) + e- → Ag(s)
Here, the reaction is feasible, because Ag+ ion has a higher reduction potential i.e. higher E° value.
- Limiting molar conductivity or the molar conductivity of solution at infinite dilution is defined as the sum of molar conductivity cations and anions.
The conductivity of an electrolyte solution decreases on dilution because the number of ions per unit volume decreases.
For Latest Updates on Upcoming Board Exams, Click Here:https://t.me/class_10_12_board_updates
Do Check Out:
Comments