Molekulska masa

voda

molekulska formula: ${\displaystyle \mathrm {H} _{2}\mathrm {O} }$ 

${\displaystyle \mathrm {M} _{R}=(2\cdot 1)+16=18}$ 

ogljikov dioksid

molekulska formula: ${\displaystyle \mathrm {CO} _{2}}$ 

${\displaystyle \mathrm {M} _{R}=12+(2\cdot 16)=44}$ 

Absolutna molekulska masa m_M se lahko izračuna kot količnik med molsko maso M in številom delcev v enem molu snovi (t. i. Avogadrova konstanta N_A):

${\displaystyle m_{M}={M \over N_{A}}}$ 

Absolutna molekulska masa vode:

• ${\displaystyle M=18{,}015\,\mathrm {g\,mol} ^{-1}}$ 
• ${\displaystyle N_{A}=6{,}022\cdot 10^{23}\,\mathrm {mol} ^{-1}}$ 
• ${\displaystyle \Rightarrow m_{M}={\frac {18{,}015\,\mathrm {g\,mol} ^{-1}}{6{,}022\cdot 10^{23}\,\mathrm {mol} ^{-1}}}=2{,}9916\cdot 10^{-23}\,\mathrm {g} }$