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Molar Mass Formula

The molar mass of a species is the mass in grams of 1 mole (6.023x1023) of that species, i mole of atoms, 1 mole of molecules or 1 mole of formula units. So it is necessary to calculate the molecular or formula mass of each compound to get its molar mass.

Molar mass is the mass (in grams) of one mole of a substance.Using the atomic mass of an element and multiplying it by the conversion factor grams per mole (g/mol), you can calculate the molar mass of that element.

Molecular Mass equals the sum of the atomic masses of all atoms in the molecule. The unit of molecular mass is the amu.

Molar Mass is an amount of the compound equal to its molecular mass in grams. The unit of molar mass is the gram.

Two important facts to remember:
  1. One mole of an element is 6.023x1023 atoms of that element.
  2. One mole of an element is an amount of that element equal to its molar mass (an amount equal to its atomic mass in grams).

Molar Mass

I mole of any element is an amount equal to its atomic mass in grams, its molar mass.

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Molar Mass Problems

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Solved problems based on molar mass and molecular mass are given below.

Solved Examples

Question 1: Find the molar mass of Ca3(PO4)2?
Determining the formula mass of calcium phosphate Ca3(PO4)2, which has 3 calcium ions, Ca2+, and 2 phosphate ions PO42-, starts by counting the atoms of each element in the formula 3Ca, 2P and 8O and ends by adding the atomic masses of the 13 atoms.

The formula of Ca3(PO4)2 = 3Ca + 2P + 8O

(3Ca x 40.08amu) + (2P x 30.97amu) + (8O x 16.00amu) = 310.18amu

The formula mass of Ca3(PO4)2 = 310.18amu

The molar mass of Ca3(PO4)2 = 310.18g

1 mole of Ca3(PO4)2 = 310.18g of Ca3(PO4)2 = 6.023 x 1023 formula units

Question 2: Find the molar mass of MgSO4.7H2O?
Hydrates are also ionic compounds that contain a definite amount of water in the crystalline solid.
The hydrate of magnesium sulfate. MgSO4.7H2O has 1 Mg2- ion, 1 SO42- ion and 7 molecules of water in the formula unit.
Seven moles of water are present for each 1 mole of MgSO4.
There are 27 atoms in the formula unit: 1Mg, 1S, 11O and 14H.
The formula mass of MgSO4.7H2O is
The formula of MgSO4.7H2O = 1Mg + 1S + 11O + 14H

(1Mg x 24.31amu) + (1S x 32.07amu) + (11O x 16.00amu) + (14H x 1.008amu) = 246.49amu

The molar mass of MgSO4.7H2O = 246.49g

1 mole of MgSO4.7H2O = 246.49g of MgSO4.7H2O = 6.022 x 1023 formula units.


More topics in Molar Mass Formula
Gram Formula Mass Mass Percent Formula
Molar Volume Formula Percent by Volume Formula
Percent by Weight Formula Percent Increase Formula
Percent Decrease Formula Percentage Yield Formula
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