What are hydrocarbons ? Write the name and general formula of (i) saturated hydrocarbons, (ii) unsaturated hydrocarbons, and draw the structure of one hydrocarbon of each type. How can an unsaturated hydrocarbon be made saturated ?

OR

What are detergents chemically ? List two merits and two demerits of using detergents for cleansing. State the reason for the suitability of detergents for washing, even in the case of water having calcium and magnesium ions.

Part 1: Hydrocarbons

Hydrocarbons: Compounds containing only carbon and hydrogen are called hydrocarbons.

(i) Saturated Hydrocarbons:

• Name: Alkanes
• General Formula: $C_nH_{2n+2}$ (where $n \ge 1$)
• Structure of Ethane ($C_2H_6$):

$$\begin{array}{cc} H & H \\ | & | \\ H-C-C-H \\ | & | \\ H & H \end{array}$$

(ii) Unsaturated Hydrocarbons:

• Name: Alkenes (containing a double bond) and Alkynes (containing a triple bond)
• General Formula:
• Alkenes: $C_nH_{2n}$ (where $n \ge 2$)
• Alkynes: $C_nH_{2n-2}$ (where $n \ge 2$)
• Structure of Ethene ($C_2H_4$):

$$\begin{array}{cc} H & H \\ \backslash & / \\ C=C \\ / & \backslash \\ H & H \end{array}$$

Conversion of Unsaturated Hydrocarbon to Saturated Hydrocarbon:

An unsaturated hydrocarbon can be converted into a saturated hydrocarbon by an addition reaction (specifically, hydrogenation). This is done by adding hydrogen ($H_2$) in the presence of catalysts such as nickel ($Ni$) or palladium ($Pd$) at an elevated temperature.

$$\text{Ethene } (C_2H_4) + H_2 \xrightarrow{Ni} \text{Ethane } (C_2H_6)$$

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OR

Part 2: Detergents

Chemical Nature of Detergents:

Detergents are generally ammonium or sulphonate salts of long-chain carboxylic acids.

Merits of using Detergents:

1. Suitability in Hard Water: They work efficiently even in hard water and do not form insoluble scum.
2. Stronger Cleansing Action: They have stronger cleansing properties than soaps and can be used in acidic mediums.

Demerits of using Detergents:

1. Environmental Pollution: Many detergents are non-biodegradable, leading to water and soil pollution.
2. Skin Irritation: Due to their strong chemical nature, they can cause irritation to human skin upon prolonged contact.

Reason for Suitability in Hard Water:

Hard water contains calcium ($Ca^{2+}$) and magnesium ($Mg^{2+}$) ions. Unlike soaps, the charged groups of detergents do not form insoluble precipitates (scum) with these calcium and magnesium ions. Therefore, they remain effective and lather easily even in hard water.