Problem 25 - A Complete Resource Book in Chemistry for JEE Main

Question

When petroleum is heated gradually, first batch of vapours evolved will be rich in (a) kerosene (b) petroleum ether (c) diesel (d) lubricating oil

Step-by-Step Solution

Answer

The first batch of vapors will be rich in petroleum ether.

Step 1: Understand the Distillation Process

Petroleum distillation is a process of heating crude oil to separate its components based on their boiling points. The substance at each stage of the distillation tower has a different boiling point, with lighter fractions vaporizing at lower temperatures.

Step 2: Identify Boiling Points of Substances

Understand which substance is petroleum ether and how it relates in terms of boiling point to kerosene, diesel, and lubricating oil. Petroleum ether has one of the lowest boiling points among these options, typically ranging from around 30°C to 60°C.

Step 3: Determine Initial Vapour Composition

Given that petroleum ether has the lowest boiling point among the options provided, it will be the first to vaporize when the crude oil is heated.

Step 4: Conclusion Based on Temperature

The initial vapors evolved upon heating petroleum will be rich in the substance with the lowest boiling point, which, according to the sequence of distillation, is petroleum ether.

Key Concepts

Boiling Points

When it comes to separating components in petroleum, understanding boiling points plays a crucial role. Each substance in petroleum has a unique boiling point, which is the temperature at which a liquid turns into vapor. Since petroleum comprises various substances mixed together, the difference in boiling points allows us to separate them effectively.

Here’s a simple breakdown:

• Substances with low boiling points will vaporize at lower temperatures.
• Components like petroleum ether have lower boiling points compared to heavier substances like diesel or lubricating oil.

Knowing the boiling point of a substance helps in determining its position in the distillation process. For example, petroleum ether, with its low boiling point, is among the first to vaporize when petroleum is gradually heated.

Petroleum Ether

Petroleum ether is not actually an ether but a light and volatile fraction of petroleum. It is commonly used in laboratories and industry due to its ability to evaporate quickly.

Here are some key points about petroleum ether:

• Despite its name, petroleum ether comprises a mixture of hydrocarbons, mainly alkanes.
• It typically has a boiling point range from 30°C to 60°C, which is relatively low.
• This makes it one of the first substances to vaporize during the distillation of crude oil.

In the context of the distillation process, the properties of petroleum ether make it an ideal candidate for initial separation due to its low boiling point and ability to form vapors early when heated.

Distillation Process

The distillation process is a central method used to refine crude oil into usable products. It relies on heating crude oil to a point where components are separated based on their boiling points. Here’s how it works:

• Crude oil is gradually heated in a distillation column.
• As the temperature increases, substances with lower boiling points begin to vaporize first.
• The vaporized substances are then condensed back into liquid form at different levels of the column.
• Each level of the column collects different components based on their boiling points.

This method effectively separates lighter, more volatile substances such as petroleum ether from heavier components like kerosene and diesel. The sequential vaporization and condensation enable the production of distinct petroleum products from a single batch of crude oil.