安息香酸の再結晶精製

熱溶媒に溶かして冷却することで固体を精製する

Crystallization Intermediate (High School) 45 分 ~$10.00

目的

熱水からの再結晶により不純な安息香酸を精製し、有機固体の標準精製技術を実証する。

背景

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.

安全上の警告

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

必要なPPE

goggles lab_coat

材料

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

器具

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

手順

1

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

3 分
2

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

8 分 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 分
4

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

15 分
5

Cool further in an ice bath to maximize crystal yield.

5 分
6

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

5 分
7

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

3 分
8

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

5 分

予想される結果

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.

後片付け

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

詳細

カテゴリ
Crystallization
難易度
Intermediate (High School)
所要時間
45 分
推定費用
$10.00
ステップ数
8
材料
3

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Frequently Asked Questions

What is the objective of 安息香酸の再結晶精製?
熱水からの再結晶により不純な安息香酸を精製し、有機固体の標準精製技術を実証する。
How difficult is 安息香酸の再結晶精製?
This experiment is rated as Intermediate (High School). It takes approximately 45 minutes to complete.
What safety precautions are needed for 安息香酸の再結晶精製?
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 安息香酸の再結晶精製?
The main materials required are: Impure benzoic acid, Distilled water, Activated charcoal.
What results should I expect from 安息香酸の再結晶精製?
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.