Relative Atomic Mass (\(A_r\))
The weighted mean mass of an atom of an element, relative to one-twelfth of a Carbon-12 atom.
Symbol: \(A_r\). Dimensionless.
Relative Formula Mass (\(M_r\))
The sum of all the relative atomic masses of the atoms in a formula.
e.g., \(M_r\) of NaCl = 23 + 35.5 = 58.5
Molar Mass (\(M\))
The mass of one mole of a substance. Its value is numerically equal to \(A_r\) or \(M_r\), but has units of g mol⁻¹.
\( n = \frac{m}{M} \)
Calculate Moles from Mass
Problem: How many moles are in 10.0 g of Calcium Carbonate (\(CaCO_3\))?
1. Calculate M: \(40 + 12 + (3 \times 16) = 100 \text{ g mol}^{-1}\)
2. Apply Formula: \( n = \frac{m}{M} = \frac{10.0}{100} \)
\( n = 0.100 \text{ mol} \)