Question

Write the molecular formulas for the alkenes with 7,8,9 and 10 carbons

Answer 1

Step 1 - Understanding the general molecular formula for an alkane

All akanes can be reduced to a general formula that relates the number of H atoms to the number of C atoms. This general formula is:

`C_nH_(2n+2)`

What this formula means is that, if the number of C atoms in the alkane is n, then the number of H atoms will be 2n+2. This is a fixed relation and we can use it to discover the molecular formula for any alkane.

Step 2 - Applying the formula for 7, 8, 9 and 10 C

Since we have a formula relating the number of H to the number of C, we just need to substitute n for the number of C in each case:

`\begin{gathered} n=7,2n+2=16\rightarrow C_7H_(16) \\ \\ n=8,2n+2=18\rightarrow C_8H_(18) \\ \\ n=9,2n+2=20\rightarrow C_9H_(20) \\ \\ n=10,2n+2=22\rightarrow C_(10)H_(22) \end{gathered}`