Question

Which of the following statement is wrong? (1) Both methane and ethane may be obtained by a suitable one-step reaction from methyl bromide (2) Formation of alkane by the action of zinc and alkyl halide is called Frankland reaction (3) Methane on heating with steam gives carbon black (4) Kerosene is a mixture of aliphatic hydrocarbons

Short answer

Statement 3

Step-by-step solution

Analyze Statement 1

Methane (CH₄) and ethane (C₂H₆) can be prepared through a suitable one-step reaction from methyl bromide (CH₃Br). Methane can be prepared by reducing CH₃Br with hydrogen. Ethane can be obtained through the Wurtz reaction where two methyl bromide molecules react with sodium metal.

Analyze Statement 2

The reaction of zinc and alkyl halide producing alkane is known as the Frankland reaction.

Analyze Statement 3

Methane when heated with steam typically produces a mixture of hydrogen and carbon monoxide, known as synthesis gas, rather than carbon black.

Analyze Statement 4

Kerosene is indeed a mixture of aliphatic hydrocarbons, commonly ranging from C₁₂ to C₁₅.

Identify the Incorrect Statement

After analyzing each statement, it is clear that statement 3 is incorrect as methane does not produce carbon black when heated with steam but rather synthesis gas.

Key concepts

Frankland reaction

The Frankland reaction is a significant process in organic chemistry where alkanes are formed by the action of a zinc metal with alkyl halides. In this reaction, zinc acts as a reducing agent. Here’s a simple representation:

Zn + 2R-X → R-R + ZnX₂

Where R-X represents the alkyl halide, and R-R is the resulting alkane. One key aspect is that this reaction is useful in forming alkanes with longer carbon chains from alkyl halides.

Wurtz reaction

The Wurtz reaction is a well-known method for synthesizing alkanes by coupling two alkyl halides in the presence of sodium. Here's the basic equation:

2R-X + 2Na → R-R + 2NaX

In this process, two molecules of an alkyl halide react with sodium metal to produce a higher alkane and sodium halide. For example, when methyl bromide (CH₃Br) is used, ethane (C₂H₆) and sodium bromide (NaBr) are produced. This reaction is particularly useful in forming symmetrical alkanes and provides a straightforward pathway to extend the carbon chain.

Synthesis gas

Synthesis gas, often known as syngas, is a crucial mixture comprising mainly hydrogen (H₂) and carbon monoxide (CO). It is commonly produced from methane (CH₄) through a process called steam reforming. The chemical equation for this reaction is:

CH₄ + H₂O → CO + 3H₂

Syngas serves as a fundamental intermediate in producing various chemicals and fuels. It’s extensively used in the Fischer-Tropsch process to manufacture liquid hydrocarbons and in the production of methanol, hydrogen fuel, and ammonia. Understanding the production and use of synthesis gas is vital in industrial chemistry.

Aliphatic hydrocarbons

Aliphatic hydrocarbons are organic compounds consisting entirely of carbon and hydrogen, arranged in straight or branched chains, but not in rings. They can be divided into three main categories:

• Alkanes (saturated hydrocarbons): They have single bonds between carbon atoms, following the general formula CnH₂n+₂. Examples include methane (CH₄) and butane (C₄H₁₀).
• Alkenes (unsaturated hydrocarbons): These contain at least one double bond between carbon atoms, with a general formula of CnH₂n. For example, ethene (C₂H₄).
• Alkynes (unsaturated hydrocarbons): These have at least one triple bond between carbon atoms, adhering to the formula CnH₂n−₂. Acetylene (C₂H₂) is a well-known alkyne.

Kerosene, a common fuel, is a mixture of several aliphatic hydrocarbons, typically containing molecules in the range of C₁₂ to C₁₅.