沈殿滴定（モール法）

硝酸銀を使った塩化物濃度の決定

Titrations Advanced (University) 45 分 ~$20.00

目的

硝酸銀を滴定液、クロム酸カリウムを指示薬として用いるモール法で溶液中の塩化物イオン濃度を決定する。

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.

安全上の警告

  • 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

必要な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)

器具

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

手順

1

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

2 分
2

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

1 分 Chromate is toxic — use minimal amount
3

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

3 分 AgNO₃ stains permanently
4

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

10 分
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
6

Record the volume. Repeat for concordant results.

15 分
7

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

5 分

予想される結果

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.

後片付け

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

詳細

カテゴリ
Titrations
難易度
Advanced (University)
所要時間
45 分
推定費用
$20.00
ステップ数
7
材料
4

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Frequently Asked Questions

What is the objective of 沈殿滴定（モール法）?
硝酸銀を滴定液、クロム酸カリウムを指示薬として用いるモール法で溶液中の塩化物イオン濃度を決定する。
How difficult is 沈殿滴定（モール法）?
This experiment is rated as Advanced (University). It takes approximately 45 minutes to complete.
What safety precautions are needed for 沈殿滴定（モール法）?
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 沈殿滴定（モール法）?
The main materials required are: Sodium chloride solution, Silver nitrate (AgNO₃), Potassium chromate (K₂CrO₄), Distilled water.
What results should I expect from 沈殿滴定（モール法）?
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.