Oxidation Reduction

(i) From Toluene:
Toluene is oxidized with alkaline or acidic KMnO to form benzoic acid.
(ii) From Benzamide:
Benzamide undergoes hydrolysis in the presence of dilute acid or alkali to give benzoic acid.
(iii) From Ethyl Benzoate:
Ethyl benzoate undergoes acidic or basic hydrolysis to give benzoic acid.
Conclusion:
Benzoic acid can be prepared by oxidation of toluene, hydrolysis of benzamide, and hydrolysis of ethyl benzoate.

Step 1: Bleaching action of chlorine.
Chlorine reacts with water to form nascent oxygen: The nascent oxygen oxidises the coloured substances to colourless products by chemical change. Since oxidation is permanent, the bleaching action of chlorine is permanent. Step 2: Bleaching action of SO .
Sulphur dioxide bleaches substances by reduction in presence of moisture: The nascent hydrogen reduces coloured substances to colourless forms. On exposure to air, the substances regain colour due to re-oxidation. Hence, bleaching action of SO is temporary. Conclusion:
Chlorine bleaches by oxidation (permanent), while SO bleaches by reduction (temporary).

Step 1: Nature of reaction.
Sulphur dioxide (SO ) acts as a strong reducing agent, while potassium permanganate (KMnO ) in acidic medium acts as a strong oxidising agent. When they react, SO is oxidised to sulphuric acid (H SO ) and KMnO is reduced to Mn . Step 2: Balanced redox reaction.
In acidic medium: Step 3: Reaction with potassium permanganate.
Since KMnO provides MnO ions, the reaction is: Observation.
The purple colour of KMnO solution is discharged, showing that reduction of MnO to Mn has taken place. Conclusion:
SO reduces KMnO in acidic medium, forming MnSO , K SO , and H SO , while the pink colour of permanganate disappears.

Part 1: Two methods of preparation of monohydric alcohol.
Method 1: By hydration of alkenes.
Ethene reacts with water in presence of conc. H SO or phosphoric acid catalyst to give ethanol: Method 2: By reduction of aldehydes.
Acetaldehyde on reduction with hydrogen gives ethanol: Part 2: Reactions of ethyl alcohol with conc. H SO at different temperatures.
(i) At 443 K (140 C): Formation of diethyl ether.
(ii) At 443–463 K: Dehydration to form ethene.
(iii) As oxidising agent: Formation of acetaldehyde.
Conclusion:
Monohydric alcohols can be prepared by hydration of alkenes or reduction of aldehydes. Ethanol reacts with conc. H SO differently depending on temperature, giving ether, ethene, or acetaldehyde.

Step 1: Oxidising nature.
Conc. HNO acts as a powerful oxidising agent.
Step 2: Reaction with iodine.
Iodine is oxidised to iodic acid (HIO ) and HNO is reduced to NO .
Step 3: Balanced reaction.
Step 4: Conclusion.
Thus, conc. HNO oxidises iodine to iodic acid.

Step 1: Nature of reaction.
Nitric acid oxidises zinc to zinc nitrate, liberating nitrogen oxides.
Step 2: Reaction.
With conc. HNO : With dilute HNO : Step 3: Conclusion.
Thus, nitric acid reacts with zinc producing zinc nitrate and nitrogen oxides (or H with dilute acid).

Step 1: Principle.
Electric discharge splits O molecules into oxygen atoms, which combine with O to form O .
Step 2: Reaction.
Step 3: Apparatus.
Silent discharge (ozoniser) is used to prevent decomposition of ozone by spark.
Step 4: Conclusion.
Thus, ozone is prepared by passing silent electric discharge through oxygen.

Step 1: Nature of reaction.
Ozone is a strong oxidising agent.
Step 2: Reaction.
It oxidises PbS (black) to PbSO (white).
Step 3: Conclusion.
This is used as a test for ozone.

Step 1: Reactants.
Nitric oxide (NO) reacts rapidly with ozone.
Step 2: Reaction.
Step 3: Conclusion.
Thus ozone oxidises NO to NO .

This reaction involves the oxidation of methylbenzene (toluene) using chromium trioxide chloride ( ). The result is the formation of benzaldehyde.

- Cr : The ion Cr has the electron configuration . Since Cr can easily lose an electron to become Cr , it acts as a reducing agent, facilitating the reduction of other species by donating electrons.
- Mn : The ion Mn has the electron configuration , which is unstable and readily accepts an electron to stabilize itself as Mn . Hence, Mn acts as an oxidizing agent, accepting electrons from other species.

Metals tend to show their maximum oxidation states in oxides and fluorides due to the highly electronegative nature of oxygen and fluorine. Oxygen and fluorine have a strong tendency to accept electrons, which allows the metal to lose its electrons more readily.
- In oxides (with oxygen as the ligand) and fluorides (with fluorine as the ligand), the metal tends to reach its highest oxidation state, as the electron withdrawing effect of oxygen and fluorine makes it easier for the metal to lose electrons. This is why, for example, metals like titanium, manganese, and chromium show their highest oxidation states in these compounds.

Lanthanides, which consist of the 14 elements from atomic numbers 58 (Cerium) to 71 (Lutetium), exhibit a wide range of oxidation states. These oxidation states arise from the loss of electrons from the 4f, 5s, and 5p orbitals. The oxidation states of lanthanides are generally determined by the availability of the 4f electrons for bonding. Common Oxidation States: 1. +3 Oxidation State (Most Common):
The most common and stable oxidation state for lanthanides is +3. In this state, the three 4f electrons are lost, leaving the lanthanide in a stable, highly charged state. This is the predominant oxidation state for the majority of the lanthanides. For example, the most common ion in lanthanide chemistry is , , and . 2. +2 Oxidation State:
Some lanthanides like europium (Eu) and ytterbium (Yb) can also exist in the +2 oxidation state. The +2 state is observed when the lanthanide loses two 4f electrons. The lanthanide ions in this state tend to be more stable in an environment that provides additional stabilization, such as when they are complexed with ligands. 3. +4 Oxidation State:
A few lanthanides, such as cerium (Ce) and thorium (Th), can exhibit the +4 oxidation state. In this state, they lose all of their 4f electrons and can bond with more electronegative species such as oxygen or halides. The +4 state is less stable compared to the +3 state and is generally observed in rare cases, usually when the lanthanide is in a more oxidizing environment. Rare Oxidation States: - +5 and +6 Oxidation States: These are very rare and unstable oxidation states for lanthanides. Some lanthanides like praseodymium (Pr) and neodymium (Nd) can exhibit the +5 oxidation state under special conditions, but they are rarely encountered in nature. Summary:
- Lanthanides predominantly exhibit the +3 oxidation state.
- The +2 and +4 oxidation states are observed in some lanthanides but are less stable.
- The +5 and +6 oxidation states are very rare and highly unstable.