Question

Write notes on the following: 
(a) Saturated and unsaturated hydrocarbons 
(b) Corrosion 
(c) Precipitation reaction

Hint:

Corrosion can be minimized by coating metals with a protective layer, such as paint, or by galvanizing (coating with zinc). Precipitation reactions are important in water treatment and purification processes.

Answer 1

(a) Saturated and Unsaturated Hydrocarbons:
- Saturated Hydrocarbons: These are hydrocarbons that contain only single bonds between the carbon atoms. Each carbon atom in a saturated hydrocarbon is bonded to the maximum number of hydrogen atoms. Saturated hydrocarbons are also called alkanes. Example: Methane (CH₄), Ethane (C₂H₆).
- Unsaturated Hydrocarbons: These are hydrocarbons that contain at least one double or triple bond between carbon atoms. They can be classified into two types: 1. Alkenes (contain one or more double bonds), for example, Ethene (C₂H₄). 2. Alkynes (contain one or more triple bonds), for example, Ethyne (C₂H₂).

(b) Corrosion:
Corrosion is the process of the gradual destruction of materials, especially metals, by chemical reactions with their environment. The most common example is the rusting of iron, which is caused by a reaction between iron, oxygen, and water. The chemical reaction for rusting is: \[ 4\text{Fe} + 3\text{O}_2 + 6\text{H}_2\text{O} \rightarrow 4\text{Fe(OH)}_3 \] In this process, iron forms iron(III) hydroxide, commonly known as rust. Corrosion can be prevented by methods such as painting, galvanizing, or using corrosion inhibitors.
(c) Precipitation Reaction:
A precipitation reaction is a type of chemical reaction in which two solutions containing soluble salts are mixed, and an insoluble salt (called the precipitate) forms and settles out of the solution. An example of a precipitation reaction is when solutions of silver nitrate (AgNO₃) and sodium chloride (NaCl) are mixed: \[ \text{AgNO}_3 (aq) + \text{NaCl} (aq) \rightarrow \text{AgCl} (s) + \text{NaNO}_3 (aq) \] In this case, AgCl (silver chloride) forms as a white precipitate. Precipitation reactions are commonly used to remove unwanted ions from solutions.
Conclusion:
1. Saturated hydrocarbons have only single bonds between carbon atoms, while unsaturated hydrocarbons have double or triple bonds. 2. Corrosion is the process of metal degradation due to environmental reactions, commonly seen as rusting. 3. A precipitation reaction occurs when two solutions form an insoluble product, which settles as a precipitate.