If n = 5 in the general alkane formula CnH2n+2, what is the molecular formula?

If n = 5 in the general alkane formula CnH2n+2, what is the molecular formula?

• A. C5H12
• B. C5H10
• C. C6H12
• D. C4H10

Answer: (A)

Alkanes are saturated hydrocarbons with the formula CnH2n+2. This pattern comes from each carbon forming four single bonds; for a chain of n carbons there are n−1 C–C bonds, leaving enough bonds to hydrogen to satisfy the four-bond rule, which gives hydrogen as 2n + 2. If n = 5, H = 2×5 + 2 = 12, so the molecular formula is C5H12. The other options don’t fit this pattern: C5H10 would indicate a double bond or a ring, C6H12 would add an extra carbon, and C4H10 has one fewer carbon.

Alkanes are saturated hydrocarbons with the formula CnH2n+2. This pattern comes from each carbon forming four single bonds; for a chain of n carbons there are n−1 C–C bonds, leaving enough bonds to hydrogen to satisfy the four-bond rule, which gives hydrogen as 2n + 2. If n = 5, H = 2×5 + 2 = 12, so the molecular formula is C5H12. The other options don’t fit this pattern: C5H10 would indicate a double bond or a ring, C6H12 would add an extra carbon, and C4H10 has one fewer carbon.