To find the molecular weight of strontium nitrate, written as Sr(NO3)2, the molar mass of strontium, nitrogen and oxygen first has to be found from the periodic table. The molecular weight of strontium nitrate can then be calculated by multiplying the molar mass of the elements by the number of atoms in the molecule and then adding those numbers.
- Find out the molar masses of strontium, nitrogen and oxygen
Use a periodic table to find the atomic masses of these elements. According to IUPAC (International Union of Pure and Applied Chemistry), strontium, nitrogen and oxygen have atomic masses of 87.62, 14.0067 and 15.9994. The molar mass of an element is equal to its atomic mass multiplied by the molar mass constant, which is 1 gram per mole. So the molar mass of strontium, nitrogen and oxygen is respectively 87.62 g/mol, 14.0067 g/mol and 15.9994 g/mol.
- Calculate the molecular weight of NO3
Since strontium nitrate consists of two nitrate ions, it is convenient to calculate the molecular weight of a nitrate ion and then multiply it by two. A nitrate ion has one nitrogen atom and three oxygen atoms. Thus the molecular weight of a nitrate ion is: (14.0067 + 15.9994*3) = 62.0049 g/mol.
- Calculate the molecular weight of Sr(NO3)2
A molecule of strontium nitrate consists of one strontium molecule and two nitrate ions. Since the molecular weight of a nitrate ion has been calculated to be 62.0049 g/mol, the molecular weight of Sr(NO3)2 is calculated to be: (87.62 + 62.0049*2) = 211.6298 g/mol.