(a) Removal of Greasy Dirt by Soap

Soap is an amphiphilic compound, meaning it has both hydrophilic (water-attracting) and hydrophobic (water-repelling) properties. The structure of a soap molecule consists of a long hydrocarbon chain (hydrophobic tail) and a polar group (hydrophilic head). When soap is mixed with water, it forms micelles, which are spherical aggregates where the hydrophobic tails point inward, trapping oily dirt and grease, while the hydrophilic heads remain outward in contact with water.

When greasy dirt is present on a surface, the hydrophobic tail of the soap molecule interacts with the oil molecules, while the hydrophilic head interacts with water. This dual interaction allows the soap molecules to effectively emulsify the grease. As the soap is agitated or scrubbed, the micelles form, surrounding the greasy particles. The soap effectively encapsulates the dirt, allowing it to be suspended in the water.

Rinsing with water washes away the micelles along with the trapped grease, leaving the surface clean. This mechanism is why soap is effective in cleaning oily substances that water alone cannot remove, demonstrating the principle of “like dissolves like” where the non-polar grease interacts with the non-polar tail of the soap, facilitating removal through the action of water.

(b) Absolute Alcohol and Its Extraction from Rectified Spirit

Absolute alcohol, or anhydrous ethanol, is pure ethanol with no water content, typically above 99% purity. It is widely used in the chemical industry, laboratories, and as a solvent. Rectified spirit, on the other hand, is a mixture of approximately 95% ethanol and 5% water.

To obtain absolute alcohol from rectified spirit, fractional distillation is employed. This process takes advantage of the different boiling points of ethanol (78.37°C) and water (100°C). In a fractional distillation setup, the rectified spirit is heated in a distillation flask. As the mixture is heated, ethanol vaporizes first due to its lower boiling point.

The vapor rises through a fractional distillation column, which provides a surface for repeated condensation and vaporization. This process enhances the separation of ethanol from water. The vapor is then condensed back into liquid form in a condenser. The distillate collected will have a higher concentration of ethanol.

By carefully controlling the temperature and collecting the distillate, it is possible to achieve a product with greater than 99% ethanol purity. The remaining water can be further reduced by additional distillation or using drying agents, ensuring the production of absolute alcohol.