Question

What is the gram formula mass of $Ca{{(OH)}_{2}}$?

Answer 1

Before solving this question, we should know that The addition of the atomic masses of components of a compound helps to determine the formula mass of an ionic compound. It is expressed in grams/mole. It is known as Gram formula mass.
The mathematical expression of the Gram Formula Mass is:
$Gram\,formula\,mass=\dfrac{mass\,of\,the\,solute}{formula\,mass\,of\,the\,solute}$

Complete answer:
The amount of the compound which has a mass in grams equals the formula mass in the atomic mass unit is the gram formula mass. Every element consists of an atom that has a characteristic mass. So, every molecule of a compound has a characteristic formula mass.
The above formula is a bit complicated to be used in actual calculations. We use a much-simplified formula for practical purposes. We consider the weight of one mole of a substance will be the same as its atomic weight.
This theory can be used for any molecule to calculate the gram molecular mass. We should know about the atomic weights of the elements and it can be easily solved.
The molar mass of:
Calcium= 40 grams
Oxygen= 16 grams
Hydrogen= 1 gram
OH= 17 grams
$Ca{{(OH)}_{2}}$- 1 Calcium and 2 Hydroxide
= 40 + $2\times (17)=40+34$
= 74 grams/moles
The weight of one mole of an element, ionic compound, or molecular compound is known as the Gram formula mass or the atomic mass of one mole of an element, molecular compound, or ionic compound.

Note:
Gram molecular mass and molar mass of a molecule are similar
The molecular mass of a substance in grams i.e mass of one mole of molecules is Gram Molecular Mass whereas The mass of one mole of a substance is the Molar mass. Molecular mass, Molar mass, and gram molecular mass are similar only their units vary.
Unit of Molar and Gram molecular mass is grams and Unit of molecular mass is amu/u.