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Gram Formula Mass

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Gram Formula mass is the atomic mass of one mole of an element or a molecular compound, or an ionic compound. To put it another way, the amount of a compound with the same mass in grams as the formula mass in an atomic mass unit is called the gram formula mass. Each element’s atom has a unique mass, and each compound’s molecule has a unique formula mass. The Gram Formula Mass is the formula mass of an ionic compound calculated by adding the atomic masses of its constituents. Its standard unit of measurement is grams (g). Its formula is equal to the ratio of the given mass of solute to the formula mass of solute.

Gram Formula Mass 

G = m/M

Where,

G is the gram formula mass,

m is the mass of solute,

M is the formula mass of solute.

Sample problems

Problem 1: Calculate the gram formula mass of the compound MgSO4.

Solution:

We have the compound MgSO4.

Find the number of atoms of each element present in the compound and multiply the atomic weight of each element with it.

1 atom of magnesium = 1 × 24 = 24g

1 atom of sulphur = 1 × 32 = 32g

4 atoms of oxygen = 4 × 16 = 64g

Gram Formula mass = Total molecular mass of the compound 

= 24 + 32 + 64

= 120 g

Problem 2: Calculate the gram formula mass of the compound CaCO3.

Solution:

We have the compound CaCO3.

Find the number of atoms of each element present in the compound and multiply the atomic weight of each element with it.

1 atom of calcium = 1 × 40 = 40g

1 atom of carbon = 1 × 12 = 12g

3 atoms of oxygen = 3 × 16 = 48g

Gram Formula mass = Total molecular mass of the compound

= 40 + 12 + 48

= 100 g

Problem 3: Calculate the gram formula mass of the compound H2SO4.

Solution:

We have the compound H2SO4.

Find the number of atoms of each element present in the compound and multiply the atomic weight of each element with it.

2 atoms of hydrogen = 2 × 1 = 2g

1 atom of sulphur = 1 × 32 = 32g

4 atoms of oxygen = 4 × 16 = 64g

Gram Formula mass = Total molecular mass of the compound

= 2 + 32 + 64

= 98 g

Problem 4: Calculate the gram formula mass of the compound AlCl3.

Solution:

We have the compound AlCl3.

Find the number of atoms of each element present in the compound and multiply the atomic weight of each element with it.

1 atom of aluminium = 1 × 27 = 27g

3 atoms of chlorine = 3 × 35.5 = 106.5g

Gram Formula mass = Total molecular mass of the compound

= 27 + 106.5

= 133.5 g

Problem 5: Calculate the gram formula mass of the compound KAl(SO4)2.12H2O.

Solution:

We have the compound KAl(SO4)2.12H2O.

Find the number of atoms of each element present in the compound and multiply the atomic weight of each element with it.

1 atom of phosphorus = 1 × 39 = 39g

1 atom of aluminium = 1 × 27 = 27g

2 atoms of sulphate = 2 (32 + 16 × 4) = 192g

12 moles of water = 12 (2 + 16) = 216g

Gram Formula mass = Total molecular mass of the compound

= 39 + 27 + 192 + 216

= 474 g

Problem 6: Calculate the gram formula mass of the compound CuSO4.5H2O.

Solution:

We have the compound CuSO4.5H2O.

Find the number of atoms of each element present in the compound and multiply the atomic weight of each element with it.

1 atom of copper = 1 × 63.5 = 63.5g

1 atom of sulphur = 1 × 32 = 32g

4 atoms of oxygen = 4 × 16 = 64g

5 moles of water = 5 (2 + 16) = 90g

Gram Formula mass = Total molecular mass of the compound

= 63.5 + 32 + 64 + 90

= 249.5 g

Problem 7: Calculate the gram formula mass of the compound Na2SO4∙10H2O.

Solution:

We have the compound Na2SO4∙10H2O.

Find the number of atoms of each element present in the compound and multiply the atomic weight of each element with it.

2 atoms of sodium = 2 × 23 = 46g

1 atom of sulphur = 1 × 32 = 32g

4 atoms of oxygen = 4 × 16 = 64g

10 moles of water = 10 (2 + 16) = 180g

Gram Formula mass = Total molecular mass of the compound

= 46 + 32 + 64 + 180

= 322 g


Last Updated : 04 Feb, 2024
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