What is empirical formula mass?

A hydrocarbon $\mathrm{X}$ contains $92.3\%$ of carbon by mass. 

(i) Determine the empirical formula of $\mathrm{X}$.

(ii) If the vapour density of $\mathrm{X}$ is $13$, find its molecular formula.

(iii) Name $\mathrm{X}$ and write its structural formula.

(iv) What type of reactions does the compound $\mathrm{X}$ undergo?

(v) How would you convert $\mathrm{X}$ to ${\mathrm{C}}_2{\mathrm{H}}_4$?

(vi) What would you observe when bromine water is added to $\mathrm{X}$?

A hydrocarbon $\mathrm{X}$ contains $85.7\%$ carbon by mass.
(i) Determine the empirical formula of $\mathrm{X}$.

(ii) If the relative molecular mass of $\mathrm{X}$ is 28, find the molecular formula of $\mathrm{X}$.

(iii) Name X.

(iv) Write the structural formula of $\mathrm{X}$.

(v) What is the special feature of the compound $\mathrm{X}$ that determines the type of reaction it undergoes?

(vi) How would you convert $\mathrm{X}$ to ${\mathrm{C}}_2{\mathrm{H}}_6$?

(vii) If X normally undergo addition reaction, what type of reaction does the compound ${\mathrm{C}}_2{\mathrm{H}}_6$ undergo?

When iron is heated in a stream of dry chlorine, it produces a chloride that contains $34.5\%$ by mass of iron.
(i) Calculate the empirical formula of the chloride formed.

(ii) If the relative molecular mass of the chloride formed is 325, what is its molecular formula?

(iii) Write a chemical equation for the reaction of iron with chlorine.