Question

Formula unit mass is calculated in the same way as molecular mass. There is a difference between them. What is it?

• A. It is used for compounds whose constituent particles are not ions
• B. It is used for substances whose constituent particles are ions
• C. It is only used for substances with mass less than 100
• D. None of the above

Answer 1

The correct option is B It is used for substances whose constituent particles are ions

Formula mass unit is used to determine the mass of the formula of an ionic compound. Example:- $NaCl$

$Na⟶22.99amu$ [Atomic mass of sodium]

$Cl⟶35.34amu$ [Atomic mass of chlorine]

Total $58.44amu$

This formula mass is the sum of the atomic masses of one sodium atom and one chlorine atom. $58.44amu$ is the formula mass of $NaCl$. Hence the correct answer is B.