EDTA配位滴定测水硬度

测定水中的钙镁含量

Titrations Advanced (University) 45 分钟 ~$15.00

目标

以铬黑T为指示剂，用EDTA滴定水样中的Ca²⁺和Mg²⁺离子，测定水的总硬度。

背景

EDTA (ethylenediaminetetraacetic acid) forms stable 1:1 complexes with metal ions. In the presence of Eriochrome Black T indicator at pH 10, the solution is wine-red when metal ions are present and turns blue when all metal ions are complexed by EDTA, marking the endpoint.

安全警告

  • Ammonia buffer has a strong odor — use in a ventilated area
  • Wear safety goggles
  • EDTA is generally safe but avoid ingestion

所需PPE

goggles lab_coat

材料

  • Water sample (250 mL)
    Tap water or well water
  • EDTA solution (100 mL)
    0.01M, disodium salt
  • Eriochrome Black T indicator (5 mL)
    Solid or solution
  • Ammonia buffer (pH 10) (20 mL)
    NH₃/NH₄Cl buffer
  • 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 exactly 25.0 mL of the water sample into the Erlenmeyer flask.

2 分钟
2

Add 2 mL of ammonia buffer (pH 10) to the flask.

1 分钟 Ammonia odor — work in ventilated area
3

Add a small amount of Eriochrome Black T indicator. The solution should turn wine-red.

1 分钟
4

Fill the burette with 0.01M EDTA solution. Record the initial volume.

3 分钟
5

Titrate by adding EDTA slowly while swirling. The wine-red color will gradually shift.

10 分钟
6

Near the endpoint, add EDTA drop by drop until the color changes sharply from wine-red to blue.

5 分钟
7

Record the final volume. Repeat for concordant results.

12 分钟
8

Calculate total hardness in mg/L CaCO₃ equivalent using the formula: Hardness = (V(EDTA) x C(EDTA) x 100.09 x 1000) / V(sample).

5 分钟

预期结果

Typical tap water has 100-250 mg/L total hardness (CaCO₃ equivalent). The color change should be a clear transition from wine-red to blue. Soft water requires less EDTA; hard water requires more.

清理

Dispose of EDTA solutions down the drain (biodegradable at these concentrations). Rinse all glassware.

详情

类别
Titrations
难度
Advanced (University)
时长
45 分钟
预估费用
$15.00
步骤数
8
材料
5

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Frequently Asked Questions

What is the objective of EDTA配位滴定测水硬度?
以铬黑T为指示剂，用EDTA滴定水样中的Ca²⁺和Mg²⁺离子，测定水的总硬度。
How difficult is EDTA配位滴定测水硬度?
This experiment is rated as Advanced (University). It takes approximately 45 minutes to complete.
What safety precautions are needed for EDTA配位滴定测水硬度?
Key safety precautions include: Ammonia buffer has a strong odor — use in a ventilated area; Wear safety goggles; EDTA is generally safe but avoid ingestion.
What materials are needed for EDTA配位滴定测水硬度?
The main materials required are: Water sample, EDTA solution, Eriochrome Black T indicator, Ammonia buffer (pH 10), Distilled water.
What results should I expect from EDTA配位滴定测水硬度?
Typical tap water has 100-250 mg/L total hardness (CaCO₃ equivalent). The color change should be a clear transition from wine-red to blue. Soft water requires less EDTA; hard water requires more.