Butin was subjected to incomplete chlorination, calculate the mass fraction of chlorine in the final product

Butin was subjected to incomplete chlorination, calculate the mass fraction of chlorine in the final product, name this substance.

Given:
C4H6

To find:
ω (Cl in C4H6Cl2) -?

Solution:
The mass fraction of an element in a given substance is the ratio of the relative atomic mass of a given element, multiplied by the number of its atoms in a molecule, to the relative molecular mass of a substance.
1) Write the equation of a chemical reaction:
C4H6 + Cl2 => C4H6Cl2;
2) Using the periodic system of D.I.Mendeleev, calculate the relative molecular weight of C4H6Cl2:
Mr (C4H6Cl2) = Ar (C) * 4 + Ar (H) * 6 + Ar (Cl) * 2 = 12 * 4 + 1 * 6 + 35.5 * 2 = 125;
2) Calculate the mass fraction of Cl in C4H6Cl2:
ω (Cl in C4H6Cl2) = N * Ar (Cl) * 100% / Mr (C4H6Cl2) = 2 * 35.5 * 100% / 125 = 56.8%.

Answer: Mass fraction of Cl in C4H6Cl2 is 56.8%.