苯甲酸的重结晶纯化

溶于热溶剂后冷却纯化固体

Crystallization Intermediate (High School) 45 分钟 ~$10.00

目标

从热水中重结晶纯化不纯的苯甲酸，演示有机固体的标准纯化技术。

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.

安全警告

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

所需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

设备

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

步骤

1

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

3 分钟
2

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

8 分钟 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 分钟
4

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

15 分钟
5

Cool further in an ice bath to maximize crystal yield.

5 分钟
6

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

5 分钟
7

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

3 分钟
8

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

5 分钟

预期结果

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.

清理

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

详情

类别
Crystallization
难度
Intermediate (High School)
时长
45 分钟
预估费用
$10.00
步骤数
8
材料
3

更多实验

明矾晶体的培育 30 min 水杨酸苯酯的结晶 30 min 盐与沙的分步结晶 35 min 硫酸铜晶体的培育 30 min 糖晶体（冰糖） 25 min 过饱和与瞬间结晶 35 min 铋彩虹晶体的培育 45 min

Frequently Asked Questions

What is the objective of 苯甲酸的重结晶纯化?
从热水中重结晶纯化不纯的苯甲酸，演示有机固体的标准纯化技术。
How difficult is 苯甲酸的重结晶纯化?
This experiment is rated as Intermediate (High School). It takes approximately 45 minutes to complete.
What safety precautions are needed for 苯甲酸的重结晶纯化?
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 苯甲酸的重结晶纯化?
The main materials required are: Impure benzoic acid, Distilled water, Activated charcoal.
What results should I expect from 苯甲酸的重结晶纯化?
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.