The amount of mol of oxygen required to burn 33.6 silicon?

Given:
m (Si) = 33.6 g

Find:
n (O2) -?

Solution:
1) Write the equation of a chemical reaction:
Si + O2 => SiO2;
2) Using the periodic system of D.I.Mendeleev, calculate the molar mass of Si, which will be numerically equal to the relative molecular mass:
M (Si) = Mr (Si) = Ar (Si) = 28 g / mol;
3) Calculate the amount of substance Si:
n (Si) = m (Si) / M (Si) = 33.6 / 28 = 1.2 mol;
4) Determine the amount of substance O2 (taking into account the coefficients in the reaction equation):
n (O2) = n (Si) = 1.2 mol.

Answer: The amount of substance O2 is 1.2 mol.