Question

What is the difference between gram formula mass and formula mass?

Answer 1

Hint: Gram formula mass is defined as the mass of the solute to the formula mass of the solute. Formula mass is defined as the sum of atomic weights of the atoms in the empirical formula.

Complete answer:
$-$The formula mass of a substance is the sum of the average atomic masses of each atom represented in the chemical formula and is expressed in atomic mass units. The formula mass of a covalent compound is also called the molecular mass. The mass in grams of $1$ mole of substance is its molar mass.
  $M={\displaystyle \frac{m}{n}}$
Where, $M=$molar mass
$m=$Mass of the substance in grams.
$n=$Number of moles of substance
$-$ Gram molecular mass is the mass in grams of one mole of a molecular substance. Gram molecular mass is the same as molar mass. The only difference is that gram molecular mass specifies the mass unit to be used. Gram molecular mass may be reported in grams or grams per mole.
The molar mass is a physical property defined as the mass of a given substance (chemical element or chemical compound) divided by the amount of substance.
 $grammoles={\displaystyle \frac{\text{mass in grams}}{\text{gram molecular mass}}}$
The molecular weight is commonly used as a synonym of molar mass, particularly for molecular compounds. The formula weight is a synonym of molar mass that is frequently used for non-molecular compounds, such as ionic salts.

Note:
Formula mass is used for the ionic compounds that contain metal and non-metals while gram molecular mass is used only for the covalent compounds which means compounds that contain only nonmetals.