A mole is a unit that counts particles. One mole contains exactly \$6.022\times10^{23}\$ entities (atoms, molecules, ions, etc.). Think of it as a “chemical bucket” that holds a fixed number of items, just like a bucket can hold 1000 liters of water.
Avogadro’s constant, \$N_A\$, is the number of particles in one mole. It’s named after Amedeo Avogadro, who first suggested that equal volumes of gases contain equal numbers of molecules.
| Quantity | Value |
|---|---|
| Avogadro’s Constant | \$6.022\times10^{23}\ \text{mol}^{-1}\$ |
| Molar Mass of Water (H₂O) | \$18.015\ \text{g mol}^{-1}\$ |
Concentration tells us how many grams or moles of a substance are present in a given volume of solution. It can be expressed in two common ways:
Both units are interchangeable once you know the molar mass of the solute.
When converting between \$g\,\text{dm}^{-3}\$ and \$mol\,\text{dm}^{-3}\$, always remember: mass (g) ÷ molar mass (g mol⁻¹) = moles (mol). This simple formula is a lifesaver for quick calculations.
Imagine buying apples. The store sells them by weight (grams) and by number of apples (moles). If you know the average weight of one apple (molar mass), you can convert between the two. Similarly, in chemistry, knowing the molar mass lets you switch between grams and moles.