Recristalização do Ácido Benzoico

Purificação de um sólido dissolvendo-o em solvente quente e resfriando

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

Objetivo

Purificar ácido benzoico impuro por recristalização de água quente, demonstrando a técnica padrão de purificação para sólidos orgânicos.

Contexto

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.

Avisos de segurança

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

EPI necessário

goggles lab_coat

Materiais

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

Equipamentos

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

Procedimento

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.

Limpeza

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

Detalhes

Categoria
Crystallization
Dificuldade
Intermediate (High School)
Duração
45 min
Custo estimado
$10,00
Passos
8
Materiais
3

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Frequently Asked Questions

What is the objective of Recristalização do Ácido Benzoico?
Purificar ácido benzoico impuro por recristalização de água quente, demonstrando a técnica padrão de purificação para sólidos orgânicos.
How difficult is Recristalização do Ácido Benzoico?
This experiment is rated as Intermediate (High School). It takes approximately 45 minutes to complete.
What safety precautions are needed for Recristalização do 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 Recristalização do Ácido Benzoico?
The main materials required are: Impure benzoic acid, Distilled water, Activated charcoal.
What results should I expect from Recristalização do 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.