Define structural isomers.
P is a hydrocarbon, $\text{C}_x\text{H}_y$. A gas sample of P had a volume of $25\text{ cm}^3$ at $37^{\circ}\text{C}$ and $100\text{ kPa}$. It was burned completely in $200\text{ cm}^3$ of oxygen (in excess). The final volume, taken under the same conditions as the gas sample (so the water formed is liquid and can be ignored), was $150\text{ cm}^3$. When the remaining gaseous mixture was treated with concentrated alkali to remove carbon dioxide, the volume fell to $50\text{ cm}^3$. The equation for the complete combustion of P can be written as shown: $\text{C}_x\text{H}_y + \left(x + \frac{y}{4}\right)\text{O}_2 \rightarrow x\text{CO}_2 + \frac{y}{2}\text{H}_2\text{O}$.
Use the data given to determine the value of $x$.
Use the data given to determine the value of $\left(x + \frac{y}{4}\right)$.
Give the molecular formula and the empirical formula for P.
P is unbranched. Draw the skeletal formulae of two possible structures of P that are positional isomers of one another.
Use the general gas equation to work out the mass of P in the original $25\text{ cm}^3$ gas sample, measured at $37^{\circ}\text{C}$ and $100\text{ kPa}$. Give your answer to three significant figures.