Question

(a) The equation for the burning of octane is :

$2C_8{H}_{18}+25O_2\to 16C{O}_2+18H_{2}O$

(i) How many moles of carbon dioxide are produced when one mole of octane burns?
(ii) What volume, at S.T.P., is occupied by the number of moles determined in (i)?
(iii) If the relative molecular mass of carbon dioxide is $44g$ , what is the mass of carbon dioxide produced by burning two moles of octane?
(iv) What is the empirical formula of octane?
(b) The reaction given below takes place only in the gaseous state.

$4N_{2}O+C{H}_4\to C{O}_2+2H_{2}O+4N_2$

If all the volumes are measured at the same temperature and pressure, calculate the volume of dinitrogen oxide required to give $150c{m}^3$ of steam.

Answer 1

• After observing the question we get

(a) $2\mathrm{mole}\mathrm{of}$butane produce $16\mathrm{mole}\mathrm{of}$$C{O}_2$.

(I) So $1\mathrm{mole}\mathrm{of}$ butane produces $\frac{16}{2}=8\mathrm{mole}\mathrm{of}{\mathrm{CO}}_2$.

(ii) $1\mathrm{mole}\mathrm{of}{\mathrm{CO}}_2$occupies a volume of $22.4lit$.Therefore the $8\mathrm{mole}\mathrm{of}{\mathrm{CO}}_2$ occupies $8\times 22.4=179.2\text{lit}$.

(iii) The mass of the ${\mathrm{CO}}_2$produces $(8\times 44)=352g$.

(iv) The empirical formula of octane is ${\mathrm{C}}_4{\mathrm{H}}_9$.

(b) Analysing the formula it is shown $1\mathrm{mole}\mathrm{of}{\mathrm{N}}_2\mathrm{O}$ produce $\frac{1}{2}\mathrm{mole}\mathrm{of}{\mathrm{H}}_2\mathrm{O}$.

• Therefore the volume of ${\mathrm{N}}_2\mathrm{O}$ required to Produce $150{\mathrm{cm}}^3\mathrm{of}\mathrm{steam}$ is $2\times 150{\mathrm{cm}}^3=300{\mathrm{cm}}^3$.