Question

Calculate the molecular weight of:

Cryolite [Na₃AlF₆]

Answer 1

Step-1: Count the number of atoms of each element present in the formula

In the Cryolite [Na₃AlF₆]

Number of Sodium (Na) atoms = 3

Number of Aluminium (Al) atoms= 1

Number of Fluorine (F) atoms= 6

Step-2: Multiply the atomic weight of each element with its respective number of atoms and finally add

Atomic weight of Sodium (Na)= 23 u

Atomic weight of Aluminium (Al)= 27 u

Atomic weight of Fluorine (F)= 19 u

Molecular weight = 3(Atomic weight of Sodium atom) + 1(Atomic weight of Aluminium atom) + 6(Atomic weight of Fluorine atom)

Molecular weight = 3(23) + 1(27) + 6(19)

Molecular weight =69 + 27 + 114

Molecular weight =210 u

Therefore, the molecular weight of Cryolite [Na₃AlF₆] is 210 u