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A hydrocarbon of pentane has two isomeric forms: [tex]$n$[/tex]-pentane and iso-pentane. The molecular formula of [tex]$n$[/tex]-pentane is [tex]$C_5H_{12}$[/tex]. Predict the molecular formula of iso-pentane.

A. [tex]$C_5H_{10}$[/tex]
B. [tex]$C_5H_{12}$[/tex]
C. [tex]$C_5H_9$[/tex]


Sagot :

Certainly! Let's break down the problem step by step to determine the molecular formula of iso-pentane, given that n-pentane has the molecular formula [tex]\( C_5H_{12} \)[/tex].

1. Understanding Isomers:
- Isomers are molecules that have the same molecular formula but different structural arrangements.
- Since n-pentane and iso-pentane are isomers, they must have the same molecular formula, because isomers only differ in the arrangement of atoms, not in the number of atoms present.

2. Given Molecular Formula:
- The molecular formula of n-pentane is [tex]\( C_5H_{12} \)[/tex].

3. Analyzing Options:
- We need to determine which of the given options has the same molecular formula as n-pentane:
- Option A: [tex]\( C_5H_{10} \)[/tex]
- Option B: [tex]\( C_5H_{12} \)[/tex]
- Option C: [tex]\( C_5H_9 \)[/tex]

4. Comparing Molecular Formulas:
- Option A: [tex]\( C_5H_{10} \)[/tex] - This has two fewer hydrogen atoms than n-pentane, so it cannot be correct.
- Option B: [tex]\( C_5H_{12} \)[/tex] - This has the same number of carbon and hydrogen atoms as n-pentane, making it the same molecular formula.
- Option C: [tex]\( C_5H_9 \)[/tex] - This has three fewer hydrogen atoms than n-pentane, so it is also incorrect.

5. Conclusion:
- Since iso-pentane is an isomer of n-pentane, and they must share the same molecular formula, the correct molecular formula for iso-pentane must be identical to that of n-pentane.

Therefore, the correct molecular formula for iso-pentane is:
[tex]\[ \boxed{C_5H_{12}} \][/tex]

Hence, the correct answer is option B: [tex]\( C_5H_{12} \)[/tex].