Redox Reaction - 1 - JEE MCQ

When a zinc rod is placed in a copper nitrate solution, a chemical reaction occurs.

• The zinc displaces copper from the solution.
• This results in copper being deposited on the zinc rod.
• The solution changes colour, often becoming more blue, indicating the presence of zinc ions.
• This is a type of redox reaction, where zinc is oxidised, and copper ions are reduced.

When zinc is placed in copper nitrate solution the intensity of the blue colour is produced and copper iron is deposited on zinc.

• This is a Redox reaction between zinc and an aqueous solution of copper nitrate occurring in a beaker.

Determining Anodes when connected to the Standard Hydrogen Electrode

The Standard Hydrogen Electrode (SHE) is commonly used as a reference electrode in electrochemistry and has an electrode potential of 0V. The electrode with a lower reduction potential than the SHE will act as the anode (site of oxidation), while the electrode with a higher reduction potential than the SHE will act as the cathode (site of reduction).
A: Fe/Fe²⁺ E₀= − 0.44
The reduction potential of this electrode is lower than that of the SHE, so it will act as the anode when connected to the SHE.
B: Al/Al³⁺ E₀= - 1.66
The reduction potential of this electrode is lower than that of the SHE, so it will also act as the anode when connected to the SHE.
C: F₂(g)/2F⁻(aq) E₀= + 2.87
The reduction potential of this electrode is higher than that of the SHE, so it will act as the cathode, not the anode, when connected to the SHE.
D: Cu/Cu²⁺ E₀= + 0.34
The reduction potential of this electrode is higher than that of the SHE, so it will also act as the cathode, not the anode, when connected to the SHE.

Therefore, electrodes A: Fe/Fe²⁺ (E₀= − 0.44) and B: Al/Al³⁺ (E₀= - 1.66) will act as anodes when connected to the Standard Hydrogen Electrode.

Explanation of Highest Value of Oxidation Number Changes from 1 to 7

The highest value of oxidation number changes from 1 to 7 across the third period in the periodic table. This is due to the following reasons:

• The Atoms of Transition Elements:Transition metals are those elements located in the d-block of the periodic table. They have varying oxidation states, but they do not usually reach an oxidation state of 7. Their oxidation states primarily range between +2 and +3, although some can reach states of +4 or +5.
• The First Three Groups:The first three groups of the periodic table include alkali metals, alkaline earth metals, and boron group elements. These groups generally have oxidation states of +1, +2, and +3 respectively. They do not reach an oxidation state of 7.
• In Alkaline Earth Metals:Alkaline earth metals are the elements in the second group of the periodic table. These elements generally have an oxidation state of +2 due to the presence of two valence electrons which are readily lost in chemical reactions.
• Across the Third Period in the Periodic Table:The elements in the third period of the periodic table show a wider range of oxidation states, which can vary from +1 to +7. This is due to the presence of both s and p orbitals in their valence shell, which allows the elements to lose or gain more electrons in chemical reactions. Therefore, across the third period in the periodic table, the highest value of oxidation number changes from 1 to 7.