Molarity
Definition and meaning of Molarity in chemistry.
Molarity is a measure of the concentration of a solute in a solution, defined as the number of moles of solute dissolved per liter of total solution. It is one of the most common ways to express concentration in chemistry.
In more detail
The formula for calculating molarity is M = moles of solute / liters of solution. For example, a 1 M (one molar) solution contains 1 mole of dissolved substance in enough solvent, usually water, to bring the total volume to exactly 1 liter. Molarity is widely used in laboratories because it is straightforward to measure volumes and prepare solutions of precise known concentration. However, molarity is temperature-dependent; since solution volume expands when heated and contracts when cooled, a solution that is 1.0 M at 20 degrees C will have a slightly different concentration at 25 degrees C.
Key facts
| Symbol | M or mol/L |
|---|---|
| Formula | M = moles of solute / liters of solution |
| Field | Analytical Chemistry |
| Temperature dependence | Volume-dependent; concentration changes with temperature |
A 0.5 M aqueous solution of sodium chloride (NaCl) contains 0.5 moles of NaCl (approximately 29.2 grams) dissolved in enough water to make exactly 1 liter of total solution.
Frequently asked questions
Why is molarity temperature-dependent?
Because solution volume changes with temperature, liquids expand when heated and contract when cooled. The same amount of solute in 1 liter at 20 degrees C will occupy a different volume at 25 degrees C, changing the molarity.
How is molarity different from molality?
Molarity is moles per liter of solution and is temperature-dependent. Molality is moles per kilogram of solvent and is temperature-independent, making molality more useful for temperature-sensitive calculations.