Concentration
Definition and meaning of Concentration in chemistry.
Concentration is the amount of solute present in a given quantity of solvent or solution, most commonly expressed as molarity, moles of solute per liter of solution.
In more detail
Concentration can be reported in several ways besides molarity, including molality (moles of solute per kilogram of solvent), mass percent, parts per million, and mole fraction, each suited to different situations such as temperature-sensitive work or trace-level analysis. It governs reaction rates through the law of mass action, determines colligative properties like boiling-point elevation and osmotic pressure, and must be known precisely for accurate titrations and solution preparation. Diluting a stock solution changes its concentration predictably according to the relation M1V1 = M2V2, since the moles of solute stay constant while the volume increases.
Key facts
| Field | General Chemistry |
|---|---|
| Common unit | mol/L (molarity, M) |
| Defining formula | C = n/V |
| Other units | molality, mass %, ppm, mole fraction |
Dissolving 1 mole of NaCl in enough water to make exactly 1 liter of solution produces a concentration of 1 mol/L, written as 1 M.
Frequently asked questions
What is the difference between molarity and molality?
Molarity (mol/L) is moles of solute per liter of solution and changes slightly with temperature because volume expands or contracts; molality (mol/kg) is moles of solute per kilogram of solvent and is temperature-independent, making it preferred for precise physical measurements.
How do you calculate a new concentration after dilution?
Use M1V1 = M2V2, where M1 and V1 are the initial molarity and volume and M2 and V2 are the final molarity and volume, since diluting adds solvent without changing the moles of solute.