What is the formula of finding mass of molecules?
In principle, since due to relativity effects the energy stored in bonds inside the molecule contributes to the total molecular mass, to obtain a very accurate determination of the mass of a molecule the sum of the mass of the particles (protons, neutrons and electrons) calculated as if the particles would be insulated should be corrected for the effect of the chemical bonds. In order to do that a quantum representation of the molecule is needed.
However this accuracy is rarely needed, the greatest number of times the mass M of the molecule is determined by adding the masses of the particles composing the molecule evaluated as if they were insulated: that is the following formula is used
M= Mp Np + Mn Nn + Me Ne
where Mp Mn Me are the masses of insulated protons, neutrons and electrons respectively and Np Nn Ne are the number of such particles composing the molecule.
If a first approximation is needed, the electronic term can be also neglected, due to the small mass of electrons with respect to the protons and neutrons.
The above equation requires to compute the number of protons, neutrons and electrons composing each element (atom or ion) of the molecule. If we know the mass of each of those elements, we can replace the above equation with the sum of the mass of every element composing the molecule. In doing it however care has to be taken in not confusing similar entities with different masses, like isotopes or ions and neutral atoms.
What is the relationship between the formula mass of a compound the Avogadro number of molecules of that compound and the mass in grams of the compound?
Molecules can be a very important piece of information while dealing with moles or mass. For example, one can very easily convert molecules to moles to find the mass of a substance (this needs the # of molecules of the compound/element and the chemical formula). Also, the number of molecules can find moles and atoms through different equations.
Formula mass / Formula weight / Molecular mass / Molecular weight of H2O = (1*2) + 16 = 18g 1 mol of H2O = 18g H2O 1 mol of H2O = 6.023 * 10^23 molecules In 18g H2O there are 6.023 * 10^23 molecules. So, In 1g H2O there are (6.023 * 10^23) / 18 molecules = 3.346 * 10^22 molecules Therefore, In 7.3g H2O there are (3.346 * 10^22) * 7.3 molecules = 2.443…
The gram molecular mass of any compound with the formula C9H8O4 is [9(gram atomic mass of carbon) + 8(gram atomic mass of hydrogen ) + 4(gram atomic mass of oxygen)] or 180.1558. This by definition is the mass of Avogadro's Number of molecules. Therefore the mass of 1.40 X 1021 molecules is: 180.1558[(1.40 X 1021 )/6.022 X 1023)] or 4.19 X 10-1 grams, to the justified number of significant digits.
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…
FORMULA UNITS TO MOLES (formula units --> moles) Divide the number of formula units by Avogadro's number. ----------- Formula Units Avogadro's number (formula units) Conversion Factor Formula Units x 1 mol -------- Avogadro's number (formula units) MOLES TO FORMULA UNITS (moles --> formula units) Multiply the number of moles by Avogadro's number. Moles Substance x Avogadro's number Conversion Factor Mol substance x Avogadro's number ---------------------- 1 mol substance MOLES TO GRAMS (moles --> grams)* Multiply…