# Question 1148f

Aug 5, 2017

No they are not..

#### Explanation:

Formula mass is the sum of the atomic weights in atomic mass units of the substance formula.

Molar mass is also sum of the atomic weights in $g m o {l}^{-} 1$ of the substance formula.

Formula mass unit → $\text{amu}$

Molar mass unit → $g m o {l}^{-} 1$

Aug 5, 2017

No, formula mass and molar mass are not the same thing.

#### Explanation:

Formula mass

The formula mass of a substance is the sum of the average atomic masses of all the atoms represented in the substance’s formula.

For example, the formula for water is $\text{H"_2"O}$.

The average atomic mass of an $\text{H}$ atom is 1.008 u, and the average atomic mass of an $\text{O}$ atom is 16.00 u.

Thus, the formula mass of water is $\text{2 × 1.008 u + 16.00 u = 18.02 u}$.

Similarly, the formula for hydrogen peroxide is ${\text{H"_2"O}}_{2}$.

Its formula mass is $\text{2 × 1.008 u + 2 ×16.00 u = 34.02 u}$

The units for formula mass are unified atomic mass units, with symbol u.

Molar mass

The molar mass $M$ is the mass of one mole (6.022 × 10^23color(white)(l) "formula units"#) of a substance.

The SI base unit for molar mass is kilograms per mole (kg/mol).

However, for historical reasons, molar masses are almost always expressed in grams per mole (g/mol).

The mole is defined so that the molar mass of a substance in grams per mole is numerically the same as the formula mass in unified atomic mass units.

Thus, the formula mass of water is 18.02 u, so the molar mass of water is 18.02 g/mol.