Refining of petroleum is carried out using which one of the following techniques?
- (a)Evaporation
- (b)Fractional distillation
- (c)Separating funnel
- (d)Sublimation
Correct — B, Fractional distillation. Crude petroleum is a mixture of many hydrocarbons with different boiling points, so it is refined by fractional distillation. The crude oil is heated and its vapours rise up a tall fractionating column that is hotter at the bottom and cooler at the top; the different fractions (petroleum gas, petrol, kerosene, diesel, lubricating oil) condense and are drawn off at different heights according to their boiling ranges.
- (a)Evaporation — Simple evaporation separates a dissolved solid from a liquid; it cannot split a mixture of miscible liquids with different boiling points into its many fractions.
- (c)Separating funnel — A separating funnel separates two immiscible liquids such as oil and water; the hydrocarbons in crude oil are miscible, so this cannot refine petroleum.
- (d)Sublimation — Sublimation separates a solid that turns directly to vapour (like camphor or ammonium chloride); petroleum's liquid components do not sublime.
Fractional distillation separates a mixture of miscible liquids that have different boiling points. In an oil refinery, heated crude oil enters a tall fractionating column; vapours rise, cool with height and condense as separate fractions, each collected over its own boiling range.
The question tests the correct separation technique. Because crude oil is a mixture of miscible liquids differing in boiling point, only fractional distillation works — evaporation, a separating funnel and sublimation each suit a different kind of mixture.
- Crude petroleum is a mixture of hydrocarbons with a range of boiling points.
- Fractional distillation separates liquids by their differing boiling points using a fractionating column.
- Lighter fractions (petroleum gas, petrol) come off near the top; heavier ones (diesel, lubricating oil, bitumen) lower down.
- It works because the components are miscible and their boiling points are well separated.
- Confusing fractional distillation with simple evaporation or a separating funnel.
- Assuming petroleum fractions can be separated like immiscible oil and water.
A direct 'which technique' item — match the separation method to a mixture of miscible liquids with different boiling points, which is fractional distillation.
UPSC_2000_GS1_Q1132000Match List I (Industrial processes) with List II (Industry with which associated) and select the correct answer using the codes given below: List I — I. Cracking, II. Smelting, III. Hydrogenation, IV. Vulcanization; List II — A) Rubber, B) Petroleum, C) Copper, D) Edible fats.
- (a) I-C, II-B, III-A, IV-D
- (b) I-B, II-C, III-D, IV-A
- (c) I-B, II-C, III-A, IV-D
- (d) I-C, II-B, III-D, IV-A
Answer(b) I-B, II-C, III-D, IV-A
Same area — the processing of petroleum. That UPSC item ties cracking to the petroleum industry; this one asks the technique (fractional distillation) used to refine crude petroleum into its fractions.
- practice — not a real PYQ
Which technique separates two miscible liquids that have a large difference in their boiling points?
- (a)filtration
- (b)fractional distillation
- (c)using a separating funnel
- (d)sublimation
Answer(b) fractional distillation.
- practice — not a real PYQ
In the fractional distillation of crude oil, the fraction with the lowest boiling range is collected
- (a)at the bottom of the column
- (b)near the top of the column
- (c)in the middle of the column
- (d)outside the column
Answer(b) near the top of the column — the lightest fractions condense highest up.