沉淀滴定（莫尔法）

用硝酸银测定氯化物浓度

Titrations Advanced (University) 45 分钟 ~$20.00

目标

用莫尔法测定溶液中氯离子浓度，以硝酸银为滴定剂，铬酸钾为指示剂。

背景

In the Mohr method, silver nitrate reacts with chloride ions to form white silver chloride precipitate. When all chloride is consumed, the first excess silver reacts with the chromate indicator to form brick-red silver chromate, signaling the endpoint. This method works at near-neutral pH.

安全警告

  • Silver nitrate stains skin and clothing permanently
  • Potassium chromate is toxic and a suspected carcinogen — handle with extreme care
  • Wear nitrile gloves and safety goggles
  • Dispose of silver and chromate waste in designated containers

所需PPE

goggles gloves lab_coat

材料

  • Sodium chloride solution (100 mL)
    Unknown concentration
  • Silver nitrate (AgNO₃) (100 mL)
    0.1M standardized
  • Potassium chromate (K₂CrO₄) (10 mL)
    5% indicator solution
  • Distilled water (200 mL)

设备

50 mL burette Burette stand and clamp 250 mL Erlenmeyer flask 25 mL pipette White tile

步骤

1

Pipette 25.0 mL of the chloride solution into the Erlenmeyer flask.

2 分钟
2

Add 1 mL of 5% potassium chromate indicator. The solution turns pale yellow.

1 分钟 Chromate is toxic — use minimal amount
3

Fill the burette with 0.1M AgNO₃. Record the initial volume.

3 分钟 AgNO₃ stains permanently
4

Titrate while swirling vigorously. A white precipitate of AgCl forms.

10 分钟
5

Near the endpoint, the precipitate becomes more curd-like. Add AgNO₃ drop by drop until a permanent brick-red color of Ag₂CrO₄ appears.

5 分钟
6

Record the volume. Repeat for concordant results.

15 分钟
7

Calculate chloride concentration: C(Cl⁻) = C(Ag+) x V(AgNO₃) / V(sample).

5 分钟

预期结果

The endpoint is marked by the first permanent appearance of a brick-red color due to Ag₂CrO₄ formation. This color should persist for at least 30 seconds after swirling.

清理

Collect all silver-containing waste in the designated heavy metal waste container. Collect chromate waste separately. Never dispose down the drain. Wash hands thoroughly.

详情

类别
Titrations
难度
Advanced (University)
时长
45 分钟
预估费用
$20.00
步骤数
7
材料
4

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Frequently Asked Questions

What is the objective of 沉淀滴定（莫尔法）?
用莫尔法测定溶液中氯离子浓度，以硝酸银为滴定剂，铬酸钾为指示剂。
How difficult is 沉淀滴定（莫尔法）?
This experiment is rated as Advanced (University). It takes approximately 45 minutes to complete.
What safety precautions are needed for 沉淀滴定（莫尔法）?
Key safety precautions include: Silver nitrate stains skin and clothing permanently; Potassium chromate is toxic and a suspected carcinogen — handle with extreme care; Wear nitrile gloves and safety goggles.
What materials are needed for 沉淀滴定（莫尔法）?
The main materials required are: Sodium chloride solution, Silver nitrate (AgNO₃), Potassium chromate (K₂CrO₄), Distilled water.
What results should I expect from 沉淀滴定（莫尔法）?
The endpoint is marked by the first permanent appearance of a brick-red color due to Ag₂CrO₄ formation. This color should persist for at least 30 seconds after swirling.