The Correct Answer and Explanation is:
The correct answer is C. C₅H₁₂.
The question asks for the correct molecular formula for pentane. To determine this, we must understand the system of naming organic compounds, specifically alkanes.
The name “pentane” can be broken down into two parts: the prefix “pent” and the suffix “ane”. In organic chemistry, the prefix indicates the number of carbon atoms in the main chain of the molecule. The prefix “pent” signifies five carbon atoms. The suffix “ane” indicates that the compound is an alkane. Alkanes are a class of hydrocarbons characterized by having only single covalent bonds between their carbon atoms. They are known as saturated hydrocarbons because each carbon atom is bonded to the maximum possible number of hydrogen atoms.
All non-cyclic alkanes follow a general molecular formula: CnH2n+2, where ‘n’ represents the number of carbon atoms. Since we know from the prefix “pent” that pentane has five carbon atoms, we set n equal to 5.
Substituting n=5 into the general formula:
Number of carbon atoms = n = 5
Number of hydrogen atoms = 2n + 2 = 2(5) + 2 = 10 + 2 = 12
Therefore, the molecular formula for pentane is C₅H₁₂.
Let’s examine the other options to understand why they are incorrect:
A. C₃H₈: This is the formula for propane (“prop” means 3 carbons).
B. C₅H₁₀: This formula (CnH2n) corresponds to a compound with five carbons and a double bond (an alkene, like pentene) or a ring structure (a cycloalkane, like cyclopentane). It is not the formula for the saturated alkane pentane.
D. C₆H₁₄: This is the formula for hexane (“hex” means 6 carbons).
Based on this analysis, C₅H₁₂ is the only formula that correctly represents pentane.
