Key Takeaways
- Molarity (M) = moles of solute divided by liters of solution
- It measures concentration - how much solute is dissolved in a given volume
- Standard unit is M (molar) or mol/L
- Essential for preparing solutions in chemistry labs
- Different from molality, which uses mass of solvent
What Is Molarity?
Molarity is one of the most common ways to express the concentration of a solution in chemistry. It represents the number of moles of solute (the substance being dissolved) per liter of solution. Molarity is denoted by the symbol M and is expressed in units of mol/L or simply "molar."
Understanding molarity is essential for anyone working in a chemistry lab, as it allows scientists to prepare solutions with precise concentrations for reactions, experiments, and analyses.
The Molarity Formula
M = n / V
Example Calculation
If you dissolve 0.5 moles of NaCl in 2 liters of water, what is the molarity?
M = 0.5 mol / 2 L = 0.25 mol/L or 0.25 M
How to Use This Calculator
Enter Moles of Solute
Input the number of moles of the substance you're dissolving. This can be calculated from mass using: moles = mass / molar mass.
Enter Volume of Solution
Input the total volume of your solution. Select liters or milliliters from the dropdown menu.
Click Calculate
Press the Calculate button to see the molarity of your solution, displayed in M (mol/L).
Understanding the Result
The molarity tells you how concentrated your solution is. A higher molarity means more solute is dissolved per unit volume. Common concentrations in laboratory settings range from millimolar (mM, 0.001 M) for dilute solutions to several molar for concentrated solutions.
Molarity vs. Molality
While molarity uses the volume of solution, molality uses the mass of the solvent. Molarity changes with temperature (since volume changes), while molality remains constant. For most laboratory work at room temperature, molarity is the preferred unit.
Frequently Asked Questions
To convert milliliters (mL) to liters (L), divide by 1000. For example, 500 mL = 0.5 L. Our calculator can handle both units - just select the appropriate option from the dropdown menu.
A 1 molar (1M) solution contains exactly 1 mole of solute per 1 liter of solution. For example, a 1M NaCl solution contains 58.44 grams of NaCl (its molar mass) dissolved in enough water to make 1 liter of solution.
Use the formula: moles = mass (g) / molar mass (g/mol). For example, if you have 10g of NaCl (molar mass = 58.44 g/mol), you have 10 / 58.44 = 0.171 moles.
Molarity is essential because chemical reactions occur between molecules, not masses. Knowing the molarity allows chemists to calculate exactly how many molecules will react, predict products, and control reaction rates. It's the standard way to express concentration in stoichiometric calculations.
Yes, molarity can change with temperature because it depends on volume, and liquids expand or contract with temperature changes. For precise work at varying temperatures, molality (moles per kilogram of solvent) is sometimes preferred as it remains constant.