Recristalización del Ácido Benzoico

Purificación de un sólido disolviéndolo en disolvente caliente y enfriando

Crystallization Intermediate (High School) 45 min ~$10,00

Objetivo

Purificar ácido benzoico impuro por recristalización desde agua caliente, demostrando la técnica estándar de purificación para sólidos orgánicos.

Antecedentes

Recrystallization exploits the difference in solubility of a substance at different temperatures. Benzoic acid is very soluble in hot water but nearly insoluble in cold water. By dissolving impure benzoic acid in hot water and cooling slowly, pure crystals form while impurities remain in solution.

Advertencias de seguridad

  • Handle hot water and hot glassware with care
  • Benzoic acid dust can irritate airways
  • Use heat-resistant gloves when handling hot flasks

EPP requerido

goggles lab_coat

Materiales

  • Impure benzoic acid (3 g)
    Mixed with charcoal or sand
  • Distilled water (200 mL)
  • Activated charcoal (0.5 g)
    Optional, for decolorization

Equipamiento

250 mL Erlenmeyer flask Hot plate Buchner funnel Filter flask Vacuum pump Melting point apparatus Ice bath Watch glass

Procedimiento

1

Weigh 3 g of impure benzoic acid and record the mass. Note the appearance (color, particle size).

3 min
2

Add the impure sample to 100 mL of distilled water in the Erlenmeyer flask. Heat to boiling while stirring.

8 min Handle hot flask with care
3

If the solution is colored, add 0.5 g activated charcoal, swirl, and filter hot through fluted filter paper.

5 min
4

Allow the clear filtrate to cool slowly to room temperature. Do not disturb.

15 min
5

Cool further in an ice bath to maximize crystal yield.

5 min
6

Collect the crystals by vacuum filtration. Wash with a small amount of ice-cold water.

5 min
7

Dry the crystals on a watch glass. Weigh and calculate percent recovery.

3 min
8

Determine the melting point (pure benzoic acid: 122°C) and compare with the impure sample.

5 min

Resultados esperados

White, needle-like crystals with a sharp melting point at 121-123°C. Typical recovery is 60-80%. The purified crystals should be whiter and have a sharper melting point than the crude material.

Limpieza

Dispose of filtrate down the drain (benzoic acid is food-grade). Rinse glassware. Dispose of charcoal in solid waste.

Detalles

Categoría
Crystallization
Dificultad
Intermediate (High School)
Duración
45 min
Costo estimado
$10,00
Pasos
8
Materiales
3

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Frequently Asked Questions

What is the objective of Recristalización del Ácido Benzoico?
Purificar ácido benzoico impuro por recristalización desde agua caliente, demostrando la técnica estándar de purificación para sólidos orgánicos.
How difficult is Recristalización del Ácido Benzoico?
This experiment is rated as Intermediate (High School). It takes approximately 45 minutes to complete.
What safety precautions are needed for Recristalización del Ácido Benzoico?
Key safety precautions include: Handle hot water and hot glassware with care; Benzoic acid dust can irritate airways; Use heat-resistant gloves when handling hot flasks.
What materials are needed for Recristalización del Ácido Benzoico?
The main materials required are: Impure benzoic acid, Distilled water, Activated charcoal.
What results should I expect from Recristalización del Ácido Benzoico?
White, needle-like crystals with a sharp melting point at 121-123°C. Typical recovery is 60-80%. The purified crystals should be whiter and have a sharper melting point than the crude material.