Chemical Solution Mixer

Molarity is the most commonly used measure of solution concentration in chemistry. It expresses how many moles of solute are dissolved per liter of solution — giving a precise, temperature-independent way to describe how “strong” a solution is.

Molarity formula: M = n ÷ V

Where:

• M — molarity (mol/L, also written as “M”)
• n — moles of solute
• V — volume of solution in liters (not volume of solvent — the total solution volume)

Moles from mass: n = mass (g) ÷ molar mass (g/mol)

Molar mass is the sum of atomic masses of all atoms in one molecule (found on the periodic table).

Dilution formula (when diluting a stock solution): M₁ × V₁ = M₂ × V₂

• M₁ — concentration of stock solution
• V₁ — volume of stock solution to take
• M₂ — desired final concentration
• V₂ — desired final volume

Other concentration units for reference:

• Molality (m): mol solute per kg of solvent (not solution) — temperature-independent
• Mass percent (% w/w): (mass of solute ÷ total mass of solution) × 100
• Parts per million (ppm): mg of solute per liter of solution (for very dilute solutions)
• Normality (N): moles of equivalents per liter — used in acid-base and redox titrations

Worked example — preparing NaCl solution: You want 500 mL of 0.5 M sodium chloride (NaCl) solution.

• Molar mass of NaCl: Na (22.99) + Cl (35.45) = 58.44 g/mol
• Moles needed: 0.5 M × 0.500 L = 0.25 mol
• Mass to weigh: 0.25 × 58.44 = 14.61 grams of NaCl
• Procedure: Dissolve 14.61 g NaCl in ~400 mL distilled water, then add water to reach exactly 500 mL.

Dilution example: You have 2 M HCl stock solution and need 250 mL of 0.1 M HCl.

• M₁V₁ = M₂V₂ → 2 × V₁ = 0.1 × 250
• V₁ = 12.5 mL of stock solution
• Add 12.5 mL of 2 M HCl to a 250 mL volumetric flask, then fill to the 250 mL mark with distilled water.

Safety note: Always add acid to water — never water to concentrated acid.