Solution Chemistry Calculators
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Concentration Units
- Molarity (M): mol solute / L solution; most common in chemistry; temperature-dependent
- Molality (m): mol solute / kg solvent; temperature-independent; used in colligative property calculations
- Mole fraction (χ): moles of component / total moles; dimensionless
- Mass percent (w/w%): (mass solute / mass solution) × 100
- Parts per million (ppm): mg/kg or mg/L for dilute aqueous solutions
Solubility and the Solubility Product (Ksp)
For a sparingly soluble salt AB ⇌ A⁺ + B⁻: Ksp = [A⁺][B⁻]. If Ksp = 1.0 × 10⁻¹⁰, molar solubility s = √(Ksp) = 10⁻⁵ M = 0.01 mg/L for a 1:1 electrolyte. Common ion effect: adding a common ion decreases solubility further.
Colligative Properties
Depend on number of solute particles, not identity:
- Vapor pressure lowering: ΔP = P° × χ_solute (Raoult's law)
- Boiling point elevation: ΔT_b = K_b × m × i (i = van't Hoff factor for electrolytes)
- Freezing point depression: ΔT_f = K_f × m × i (K_f water = 1.86°C/m)
- Osmotic pressure: π = iMRT (R = 0.08206 L·atm/mol/K)
Electrolyte Behavior
Strong electrolytes (NaCl, HCl, NaOH) dissociate completely. Weak electrolytes (acetic acid, ammonia) dissociate partially — governed by Ka or Kb. NaCl in water gives 2 particles per formula unit (i = 2); Na₂SO₄ gives 3 (i = 3), increasing osmotic and colligative effects proportionally.
Glossary
Frequently Asked Questions
Molarity (M) = moles of solute per liter of solution; the most common concentration unit; changes with temperature because liquid volume expands/contracts. Molality (m) = moles of solute per kilogram of solvent; temperature-independent; used in colligative property calculations (boiling point elevation, freezing point depression) where temperature changes occur. Example: 1 M NaCl ≠ 1 m NaCl because volume of solution and mass of solvent differ. For dilute aqueous solutions, M ≈ m, but they diverge significantly for concentrated solutions or at high temperatures.
Colligative properties depend on the number of dissolved particles, not their identity. Key ones: Boiling point elevation ΔT_b = K_b × m × i (K_b for water = 0.512°C/m); freezing point depression ΔT_f = K_f × m × i (K_f for water = 1.86°C/m); osmotic pressure π = iMRT. The van't Hoff factor i accounts for dissociation: NaCl i = 2; MgCl₂ i = 3; glucose i = 1. Example: 0.1 m NaCl: ΔT_f = 1.86 × 0.1 × 2 = 0.372°C depression.
Osmolarity = total concentration of all dissolved particles in mol/L (osmol/L or mOsm/L); includes all ions from dissociation. For NaCl: 1 M NaCl → ~2 osmol/L. Human blood plasma osmolarity: ~285–295 mOsm/L. IV fluids must be isotonic (≈280–310 mOsm/L) to prevent cell damage. Hypotonic solutions cause cells to swell and lyse; hypertonic solutions cause cells to shrink (crenation). Osmolarity drives water movement across semi-permeable membranes (osmosis): water moves from low osmolarity to high osmolarity.
Ksp is the equilibrium constant for the dissolution of a sparingly soluble ionic compound: for AgCl ⇌ Ag⁺ + Cl⁻, Ksp = [Ag⁺][Cl⁻] = 1.8 × 10⁻¹⁰. Molar solubility s = √Ksp = 1.34 × 10⁻⁵ M. Ksp predicts whether a precipitate forms: if ionic product Q = [Ag⁺]×[Cl⁻] > Ksp, precipitation occurs; if Q < Ksp, more solid can dissolve; if Q = Ksp, the solution is saturated. Ksp is used in qualitative analysis, water treatment, pharmaceutical formulation, and geological modeling of mineral equilibria.