# Question Video: Calculating the Relative Formula Mass of Magnesium Fluoride Chemistry • 10th Grade

What is the relative formula mass (M_r) of MgF_2 (magnesium fluoride)? [Mg = 24, F = 19]

01:37

### Video Transcript

What is the relative formula mass, M r, of MgF2, magnesium fluoride? The relative atomic mass of magnesium is 24 and fluorine is 19.

Relative formula mass, denoted as M r, is defined as the sum of the relative atomic masses of constituent elements of the chemical formula. According to the definition, to determine the relative formula mass of magnesium fluoride, we will need its chemical formula as well as the relative atomic masses, denoted as A r, for the constituent elements, which in this case are magnesium and fluorine.

We notice in the question that we have been provided the chemical formula, which is MgF2, and we have been provided the relative atomic masses for both magnesium and fluorine. With the chemical formula of MgF2, we know we have one magnesium ion and two fluoride ions per unit of magnesium fluoride.

Therefore, our relative formula mass equation for magnesium fluoride is equal to the sum of one of the relative atomic mass of magnesium plus two of the relative atomic mass of fluorine. Next, we substitute the relative atomic masses into the equation. We perform the calculation and determine the relative formula mass of magnesium fluoride is 62. Since we are calculating relative formula mass, which is a unitless measure, units are not included after the number 62.

Therefore, the relative formula mass, M r, of MgF2 is 62.