Percent+Composition

To calculate the percent composition (percentage composition) of a compound:
> == = (total mass of element present ÷ molecular mass) x 100 ==
 * == Calculate the molecular mass (molecular weight,formula mass, formula weight), of the compound ==
 * == Calculate the total mass of each element present in the formula of the compound ==
 * == Calculate the percentage compositon : % by weight (mass) of element ==

Remember, if there is more than one atom of the element in the compound, you need to multiply your answer by the number of atoms. If your answer is more than 100%, you have gone wrong!
Example: What is the percentage of the various elements in Sodium Carbonate [Na2CO3] ? Given Atomic Weights: C = 12 ; O = 16 ; Na = 23 The first step is to calculate the Molecular Weight (or the Formula Weight) of the chemical compound by adding the atomic weights of the atoms (elements) that constitute the compound.Molecular weight of Na2CO3 = (2 x Atomic weight of Na) + Atomic weight of C + (3 x Atomic weight of O) = (2 x 23) + 12 + (3 x 16) = 46 + 12 + 48 = 106Now, 106 grams of Sodium Carbonate [Na2CO3] contain 46 grams of Sodium [Na], 12 grams of Carbon [C], and 48 grams of Oxygen [O] So, Percentage of Sodium [Na] in Sodium Carbonate [Na2CO3] = 46/106 x 100 = 43.40%. Percentage of Carbon [C] in Sodium Carbonate [Na2CO3] = 12/106 x 100 = 11.32%. Percentage of Oxygen [O] in Sodium Carbonate [Na2CO3] = 48/106 x 100 = 45.28%.

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