Answer to Question #110392 in Chemistry for Arleny

Question

what quantity is needed to convert between the moles of a given sample of a substance and its mass in grams

Answer 1

The moles of a given sample is its amount of substance in the unit of Avogadro's number (6.022·10²³) of its formula units. In order to convert the mass $m$ in grams to the number of the moles $n$, you should use the molar mass $M$ (in g/mol):

$n (\text{mol}) = \frac{m (\text{g}) }{ M(\text{g/mol})}$.

The molar mass $M$ can be calculated using the relative atomic masses $A_{r,i}$ found in the periodic table:

$M = M_u\sum_{i} p_iA_{r, i}$

where $M_u$ is the molar mass constant (1 g/mol) and $p_i$ are the numbers of the $i$-type atoms in the formula unit of a sample.

Answer: the molar mass is needed to convert between the moles of a given sample of a substance and its mass in grams.