(a) With the help of a suitable example, explain the process of hydrogenation mentioning the conditions of the reaction and any one change in physical property with the formation of the product. (b) How does a saturated hydrocarbon react with chlorine? Write chemical equation for it. What type of reaction is it called and why? OR What are soaps and detergents chemically? Explain the action of cleaning by soaps. State the reason why we can wash our clothes even in hard water using detergents.

Part (a): Hydrogenation

Hydrogenation is the chemical process of adding hydrogen to unsaturated hydrocarbons (alkenes or alkynes containing double or triple bonds) in the presence of catalysts like nickel ($\text{Ni}$) or palladium ($\text{Pd}$) to convert them into saturated hydrocarbons.

• Conditions of the reaction:

1. Presence of a catalyst such as finely divided Nickel ($\text{Ni}$) or Palladium ($\text{Pd}$).
2. Elevated temperature (heating).

• Example (Industrial Hydrogenation of Vegetable Oils):

$$\text{Vegetable Oil (Unsaturated)} + \text{H}_2 \xrightarrow{\text{Ni catalyst, } \Delta} \text{Vegetable Ghee (Saturated)}$$

• Change in physical property:

The reactant (vegetable oil) is a liquid at room temperature, whereas the product (vegetable ghee/saturated fat) is a solid/semi-solid at room temperature.

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Part (b): Reaction of Saturated Hydrocarbons with Chlorine

Saturated hydrocarbons are generally unreactive. However, in the presence of sunlight, they undergo a rapid reaction with chlorine.

• Chemical Equation (Chlorination of Methane):

$$\text{CH}_4 + \text{Cl}_2 \xrightarrow{\text{Sunlight}} \text{CH}_3\text{Cl} + \text{HCl}$$

• Type of Reaction: Substitution Reaction.
• Reason: It is called a substitution reaction because chlorine atoms replace the hydrogen atoms of the saturated hydrocarbon one by one.

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OR Option: Soaps and Detergents

#### 1. Chemical Nature

• Soaps: Sodium or potassium salts of long-chain carboxylic acids (fatty acids), such as sodium stearate ($C_{17}H_{35}COONa$).
• Detergents: Ammonium or sulphonate salts of long-chain carboxylic acids.

#### 2. Cleansing Action of Soaps

• A soap molecule consists of two parts:

1. A hydrophobic tail (long hydrocarbon chain) which is water-repelling but oil-soluble.
2. A hydrophilic head (ionic part, $-\text{COO}^-\text{Na}^+$) which is water-soluble.

• When soap is dissolved in water containing oily dirt, the hydrophobic tails align towards the dirt/oil droplet, while the hydrophilic ionic heads face outwards towards the water.
• This unique arrangement forms a spherical cluster called a micelle.
• The oily dirt is trapped in the center of the micelle. Upon agitation, these micelles remain suspended as an emulsion and are easily washed away with water.

#### 3. Why Detergents work in Hard Water

• Hard water contains calcium ($Ca^{2+}$) and magnesium ($Mg^{2+}$) ions.
• When soap is used in hard water, it reacts with these ions to form an insoluble, sticky precipitate called scum, which severely limits its cleansing action.
• Detergents, however, do not form insoluble precipitates (scum) with calcium and magnesium ions. Therefore, they remain highly effective and can easily wash clothes even in hard water.