2
M
2,000
mM
2,000,000
μM
2
M
2,000
mM
2,000,000
μM
Molarity is the most widely used unit of concentration in chemistry, defined as the number of moles of solute dissolved per liter of solution. Represented by the symbol M (capital M), molarity provides a standardized way to express how concentrated a solution is, making it indispensable in stoichiometric calculations, titrations, and laboratory preparations.
The molarity formula is elegantly simple: M = n / V, where n is the number of moles of solute and V is the volume of the solution in liters. This calculator allows you to quickly determine the molar concentration of any solution given the amount of solute and the total solution volume. Whether you are preparing buffer solutions, calculating reagent amounts for reactions, or converting between concentration units, understanding molarity is fundamental to quantitative chemistry.
Molarity is temperature-dependent because liquid volumes expand and contract with temperature changes. For this reason, molality (moles per kilogram of solvent) is sometimes preferred for precise thermodynamic work. However, for the vast majority of bench chemistry and analytical applications, molarity remains the standard concentration unit recognized by IUPAC.
The molarity calculation follows a straightforward relationship between solute amount and solution volume:
M = n / V
Where:
To use this calculator, you need two values: the number of moles of solute and the volume of the solution. If you know the mass of solute instead of moles, first convert using n = mass / molar mass. For example, dissolving 58.44 g of NaCl (molar mass = 58.44 g/mol) gives exactly 1 mole.
The result is expressed in three units for convenience:
It is critical to note that molarity refers to the total volume of solution, not the volume of solvent alone. When preparing a 1 M solution, you dissolve the solute in some solvent, then add more solvent until the final solution volume reaches the desired amount. Simply adding solute to 1 liter of solvent would yield a slightly different concentration due to volume changes upon mixing.
Standard laboratory practice involves using volumetric flasks calibrated at a specific temperature (typically 20°C or 25°C) to ensure accurate volumes. For highly precise work, density corrections and temperature compensation may be necessary.
A molarity of 1.0 M means there is exactly one mole of solute per liter of solution. Higher molarity values indicate more concentrated solutions. For context, concentrated hydrochloric acid is approximately 12 M, while physiological saline (0.9% NaCl) is about 0.154 M. Many biological buffers are prepared in the millimolar range (1-100 mM), and drug concentrations in pharmacological assays are often in the micromolar or even nanomolar range.
If your calculated molarity seems unusually high (above the solubility limit of the solute), the solution may not be physically realizable — always check solubility data. Conversely, extremely low molarities may require serial dilution techniques for accurate preparation.
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Dissolving 0.5 mol of NaCl (29.22 g) in enough water to make 250 mL (0.25 L) of solution yields a 2.0 M NaCl solution.
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Dissolving 0.0278 mol of glucose (5.0 g, MW = 180.16) in 500 mL of solution gives 55.6 mM, close to physiological blood glucose concentration (~5.5 mM requires further dilution).
Molarity (M) is moles of solute per liter of solution, while molality (m) is moles of solute per kilogram of solvent. Molarity depends on temperature because liquid volume changes with temperature, whereas molality does not. Molality is preferred for precise thermodynamic calculations such as boiling point elevation and freezing point depression.
Absolutely. Many common reagents have high molarities. Concentrated sulfuric acid is approximately 18 M, concentrated hydrochloric acid is about 12 M, and glacial acetic acid is approximately 17.4 M. The upper limit depends on the solubility of the solute in the given solvent at the specified temperature.
Molarity is defined per liter of solution, and liquid volumes expand when heated and contract when cooled. A solution prepared as 1.000 M at 20°C will have a slightly lower molarity at 30°C because the same amount of solute is now in a larger volume. For most routine work this effect is negligible, but for high-precision analytical chemistry, temperature must be controlled.
Divide the mass (in grams) by the molar mass (in g/mol) of the solute: n = mass / molar mass. For example, 40 g of NaOH (molar mass 40.00 g/mol) equals 1.00 mol. You can find molar masses on the periodic table or in chemical reference databases.
A 0.1 M (or 100 mM) solution contains 0.1 moles of solute per liter. For NaCl (molar mass 58.44 g/mol), this means 5.844 grams dissolved in enough water to make 1 liter. This is a common concentration for many laboratory reagents and buffer solutions.
Yes. According to IUPAC, the terms "molarity" and "molar concentration" (also called "amount concentration") are synonymous. The SI unit is mol/m³, but mol/L (= mol/dm³) is the accepted unit for practical use. The symbol M (e.g., 1 M) is a widely used shorthand for mol/L.
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