Solution Preparation Calculators

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Solution preparation is the process of dissolving a known amount of solute in a solvent to achieve a specified concentration. It is one of the most fundamental laboratory skills. Solutions are described by molarity (mol/L), mass/volume percent (g/100 mL), mass percent (g/g), or volume percent. Accurate preparation requires weighing or measuring the correct solute amount, choosing the appropriate solvent, and bringing to the exact final volume in a calibrated volumetric flask. Dilutions are calculated using the conservation of moles: C₁V₁ = C₂V₂.

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Preparing a Molar Solution

Mass to weigh (g) = Molarity (mol/L) × Volume (L) × Molar mass (g/mol)

Example: prepare 500 mL of 0.1 M NaCl (MW = 58.44 g/mol): mass = 0.1 × 0.5 × 58.44 = 2.922 g. Weigh 2.922 g NaCl, dissolve in ~400 mL water, transfer to 500 mL volumetric flask, add water to the mark.

Dilution Formula: C₁V₁ = C₂V₂

C₁ = initial concentration; V₁ = initial volume needed; C₂ = desired final concentration; V₂ = desired final volume. Example: dilute 1 M HCl stock to 0.01 M in 100 mL: V₁ = C₂V₂/C₁ = (0.01 × 100)/1 = 1 mL. Take 1 mL of 1 M HCl and dilute to 100 mL with water.

Percent Solutions

  • w/v %: grams of solute per 100 mL solution. Example: 5% w/v NaCl = 5 g NaCl in 100 mL total.
  • v/v %: mL of solute per 100 mL solution. Example: 70% v/v ethanol = 70 mL ethanol + 30 mL water.
  • w/w %: grams of solute per 100 g solution. Used for concentrated acids and bases.

Buffer Preparation

Buffers are prepared by: (1) Henderson-Hasselbalch calculation to determine ratio of weak acid to conjugate base for target pH; (2) mixing calculated amounts; (3) pH meter verification and adjustment with strong acid/base. Alternative: prepare one component, add titrant until pH meter reads target, then bring to final volume.

Glossary

Molarity (M)
Moles of solute per liter of solution (mol/L); the standard concentration unit in chemistry; moles = molarity × volume (L); mass needed = molarity × volume × molar mass.
C₁V₁ = C₂V₂
The dilution equation expressing conservation of solute moles; V₁ = volume of stock needed = C₂V₂/C₁; used to prepare dilutions from concentrated stock solutions.
Volumetric Flask
A precision glass flask with a calibration mark at a specific volume; used to prepare solutions of exact concentration; solution is brought to the mark, not filled to the brim.

Frequently Asked Questions

A 1 M (1 molar) solution contains 1 mole of solute per liter. Mass to weigh = molar mass (g/mol). Example: 1 M NaOH (MW = 40.0 g/mol): weigh 40.0 g NaOH. Dissolve in ~700 mL of distilled water (use a beaker — NaOH dissolves exothermically, producing heat). Cool to room temperature, transfer quantitatively to a 1 L volumetric flask, and fill to the calibration mark. For solutions sensitive to carbonation or oxidation, use freshly boiled, cooled water and store appropriately.

C₁V₁ = C₂V₂ is conservation of moles — the amount of solute is the same before and after dilution. Rearrange to find the needed volume of stock: V₁ = C₂V₂/C₁. Example: prepare 200 mL of 0.25 M glucose from a 2 M stock: V₁ = (0.25 × 200)/2 = 25 mL. Take 25 mL of the 2 M stock and bring to a total volume of 200 mL with solvent. This formula works for any consistent concentration units (M, mM, μg/mL, etc.) as long as both C values use the same units.

w/v% (weight/volume): grams of solute per 100 mL solution — most common in biology (5% NaCl = 5 g/100 mL). v/v% (volume/volume): mL of solute per 100 mL solution — used for liquid-liquid solutions like 70% ethanol (70 mL ethanol + 30 mL water = 100 mL). w/w% (weight/weight): grams of solute per 100 g solution — used for concentrated acids and bases (37% HCl w/w). For dilute aqueous solutions, w/v% ≈ mg/mL × 0.1 (since 1% w/v = 10 mg/mL = 10 g/L).

Method 1 (Henderson-Hasselbalch): For 50 mM phosphate pH 7.4, use dibasic (Na₂HPO₄, pKa 7.2) and monobasic (NaH₂PO₄). At pH 7.4: ratio = 10^(7.4−7.2) = 1.58:1 (dibasic:monobasic). For 100 mL: total phosphate = 5 mmol; dibasic = 3.14 mmol (0.56 g Na₂HPO₄·7H₂O); monobasic = 1.86 mmol (0.22 g NaH₂PO₄·H₂O). Dissolve both, check pH with meter, adjust if needed, bring to 100 mL. Method 2: prepare one component at full concentration, use NaOH or HCl to titrate to target pH while monitoring with a calibrated pH electrode.