The molecular weight of a molecule is defined as the weight of one mole of the substance.
To find the molecular weight, we must consider the different atoms that compose #C_31H_46O_2^-# and the weights of those atoms. The weight of #C_31H_46O_2^-# is simply the combined weight of its constituent atoms.
As hinted by its molecular formula, one mole of #C_31H_46O_2^-# contains the following:
#"31 moles of Carbon"#
#"46 moles of Hydrogen"#
#"2 moles of Oxygen"#
As I said before, to find the molar mass of the entire molecule, we must multiply all constituent atoms by their molar masses and add.
#"31 moles of Carbon" xx (12 " grams")/("1 mole of Carbon") = 372 " grams of Carbon"#
#"46 moles of Hydrogen" xx (1 " gram")/("1 mole of Hydrogen") = 46 " grams of Hydrogen"#
#"2 moles of Oxygen" xx (16 " grams")/("1 mole of Oxygen") = 32" grams of oxygen"#
#"The molecular weight of vitamin K1 is the sum of these values,"#
#372 + 46 + 32 = 450 " grams per mole of " C_31H_46O_2^-#
