Difference between formula weight and molecular weight?

Answer 1

Both formula mass and molecular mass refer to the mass of a compound relative to 1/12 of the mass of a Carbon-12 atom. However, molecular mass is specific to molecules – that is, only for a minimum of 2 atoms held together by covalent bonds. As an example, you can say that the molecular mass of water is 18. You can also say that the formula mass of water is 18. You can say that the formula mass of common table salt, NaCl, is 58.5, but it would be inaccurate to say that the molecular mass of NaCl is 58.5, since NaCl is not a molecule. The difference is not in numerical value but merely terminology.

Answer 2

It would perhaps be more accurate to use the terms formula mass and molecular mass rather than formula weight and molecular weight. This because in physical terms, weight is a force while mass is a measure of the amount of substance in something. Both formula mass and molecular mass refer to the mass of a compound relative to 1/12 of the mass of a Carbon-12 atom. However, molecular mass is specific to molecules – that is, only for a minimum of 2 atoms held together by covalent bonds. As an example, you can say that the molecular mass of water is 18. You can also say that the formula mass of water is 18. You can say that the formula mass of common table salt, NaCl, is 58.5, but it would be inaccurate to say that the molecular mass of NaCl is 58.5, since NaCl is not a molecule. The difference is not in numerical value but merely terminology.

Answer 3

The difference between formula weight and molecular weight is in terms of type of compounds. Formula weight refers to the total of all atomic weights in the specific formula. Formula weight is used for ions rather than molecules. Molecular weight refers to the total of all atomic weights in the specific molecule.

Answer 4

Equivalent weight is the amount of an element that reacts, or is involved in reaction with, 1 mole of electrons. It is 'defined' by many texts as the weight of the element combining with 1 g hydrogen, 8 g oxygen or 35.5 g chlorine, each of which would either provide or accept one mole of electrons in a reaction.

For example, hydrogen, with atomic weight 1.008 and valence 1, has an equivalent weight of 1.008. Oxygen assumes a valence of 2 and has an atomic weight of 15.9994, so it has an equivalent weight of 7.9997.

What is the molecular weight?

The molecular or molar mass of a substance is the mass of 6.022*10^23 molecules of the substance, in grams. (there is a very complicated difference between molar and molecular mass, but for practical purposes, we can consider these interchangeable)

The distinction between these two values is as follows:

If you prepare a solution of 1 litre containing 1 equivalent mass, the solution is called a Normal solution and is abbreviated, 1.00N. If you prepare a solution containing 1 molar mass of substance dissolved to a volume of 1 litre, then the solution then the solution is called a Molar solution, abbreviated, 1.00M.

When dealing with monoprotic acids, such as HCl or HNO3 the molar mass is the same numerically as the equivalent mass. Therefore a 1N HCl is exactly the same as 1M HCl

When dealing with a diprotric acid, such as H2SO4, where 1 molar mass has two reactable hydrogens, The 1N solution has half the concentartion of the 1M solution

When you deal with a triprotic acid, such as H3PO4. the 1N solution will have 1/3 the concentration of a 1M solution.

The same situation applies to bases: 1M NaOH is exactly the same as 1N NaOH. But 1M Mg(OH)2 is double the concentration of 1N Mg(OH)2.

Answer 5

because the formula mass is the sum of the atomic masses of the atoms in a chemical compound or element while the Atomic Mass is the mass of an element's atoms, listed in the Periodic Table as an average value based on the relative abundance of the elements isotopes.

Answer 6

Formula weight is the sum of the atomic weights of all the atoms in a chemical formula, including any subscripts. Molecular weight specifically refers to the total weight of all the atoms in a molecule. For ionic compounds, formula weight is used because the bonding within the compound is different than in covalently bonded molecules.