What is Molarity?
Molarity (M) is concentration measured as moles of solute per liter of solution: M = moles/volume. A 1 M solution contains 1 mole of solute in 1 liter of solution. Molarity is the most common concentration unit in chemistry because it directly relates to the number of particles, making stoichiometric calculations straightforward. For example, 0.5 M NaCl means 0.5 moles (29.2 g) of NaCl per liter of solution.
Preparing Molar Solutions
To prepare a molar solution: calculate mass needed (mass = molarity x volume x molar mass), weigh the solute, dissolve in less than final volume, then dilute to exact final volume in a volumetric flask. For example, to make 1 L of 0.1 M NaCl: mass = 0.1 x 1 x 58.44 = 5.844 g. Dissolve this NaCl in water and dilute to exactly 1 L. Always add solute to solvent, not vice versa, especially for acids to avoid splattering.
Applications in Science
Molarity is essential throughout chemistry and biology. Biologists prepare growth media and buffers at specific molarities. Clinical labs report blood glucose in mM (millimolar). Chemists calculate reaction stoichiometry using molarity. Pharmaceutical companies formulate drugs with precise concentrations. Molarity enables researchers to control exactly how many molecules participate in reactions, crucial for reproducible experiments. Environmental testing measures pollutants in molarity or related units to assess safety and compliance.
Quick Tips
- Always verify units are consistent
- Use scientific notation for very large/small numbers
- Results are approximations — real conditions may vary
Frequently Asked Questions
Molarity is moles per liter of solution (M = mol/L), while molality is moles per kilogram of solvent (m = mol/kg). Molarity changes with temperature; molality doesn't.
Solutions expand when heated, increasing volume and decreasing molarity. This is why molality or mole fraction is preferred for temperature-dependent studies. The effect is usually small for small temperature ranges.
A 1 M (molar) solution contains 1 mole of solute per liter of solution. For NaCl (MW = 58.44 g/mol), 1 M means 58.44 g dissolved in enough water to make 1 L total solution.
Use M?V? = M?V?, where subscripts 1 and 2 refer to concentrated and dilute solutions. To dilute 10 mL of 2 M to 0.5 M: (2)(10) = (0.5)(V?), so V? = 40 mL. Add 30 mL water to the original 10 mL.
Yes, molarity can be any positive value. Concentrated acids like HCl can be 12 M. There's no upper limit except solubility and practical considerations. High molarity means highly concentrated.