Calculate the molecular mass or formula mass (in amu) of each of the following substances: (a) BrN3 amu (b) C2H6 amu (c) NF2 amu (d) Al2S3 amu (e) Fe (NO3) 3 amu (f) Mg3N2 amu (g) (NH4) 2CO3 amu

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Explanation:

a) for BrN3

80+3 (14) = 122amu

b) forC2H6

2 (12) + 6 (1) = 30amu

C) for NF2

14+2 (19) = 52amu

D) Al2S3

2 (27) + 3 (32) = 150amu

E) for Fe (NO3) 3

56 + 3 [14+3 (16) ] = 242amu

F) Mg3N2

3 (24) + 2 (14) = 100amu

G) for (NH4) 2CO3

2[14 + 4 (1) ] + 12 + 3 (16) = 96amu

The atomic unit of mass (a. m. u) is the unit used to compare the relative masses of atoms. An atomic mass unit is a twelfth of the mass of a carbon-12 atom.

The calculation of the molecular mass of a compound is done by adding the relative atomic masses of the atoms of the formula of said substance, taking into account its abundance in the compound. The atomic mass of the atoms that make up the molecule are obtained in the Periodic Table.

So, in these cases you have:

BrN₃:

You know the atomic masses of the elements that make up the molecule, obtained from the periodic table:

Br: 79.9 amu

N: 14 amu

I take into account the abundance of each element in the compound you get:

BrN₃=79.9 amu + 3 * 14 amu = 121.9 amu

C₂H₆:

You know the atomic masses of the elements that make up the molecule, obtained from the periodic table:

C: 12 amu

H: 1 amu

I take into account the abundance of each element in the compound you get:

C₂H₆ = 2*12 amu + 6*1 amu = 30 amu

NF₂:

You know the atomic masses of the elements that make up the molecule, obtained from the periodic table:

N: 14 amu

F: 19 amu

I take into account the abundance of each element in the compound you get:

NF₂ = 14 amu + 2*19 amu = 52 amu

Al₂S₃:

You know the atomic masses of the elements that make up the molecule, obtained from the periodic table:

Al: 27 amu

S: 32 amu

I take into account the abundance of each element in the compound you get:

Al₂S₃ = 2*27 amu + 3*32 amu = 150 amu

Fe (NO₃) ₃:

You know the atomic masses of the elements that make up the molecule, obtained from the periodic table:

Fe: 55.85 amu

N: 14 amu

O: 16 amu

I take into account the abundance of each element in the compound you get:

Fe (NO₃) ₃ = 55.85 amu + 3 * (14 amu + 3*16 amu) = 241.85 amu

Mg₃N₂:

You know the atomic masses of the elements that make up the molecule, obtained from the periodic table:

N: 14 amu

Mg: 24 amu

I take into account the abundance of each element in the compound you get:

Mg₃N₂ = 3*24 amu + 2*14 amu = 100 amu

(NH₄) ₂CO₃:

You know the atomic masses of the elements that make up the molecule, obtained from the periodic table:

N: 14 amu

H: 1 amu

C: 12 amu

O: 16 amu

I take into account the abundance of each element in the compound you get:

(NH₄) ₂CO₃: 2 * (14 amu + 4*1 amu) + 12 amu+3*16 amu = 96 amu