EDTA錯体滴定による水の硬度測定

水中のカルシウムとマグネシウムの含量を測定する

Titrations Advanced (University) 45 分 ~$15.00

目的

エリオクロムブラックTを指示薬として用い、EDTAで水試料中のCa²⁺とMg²⁺イオンを滴定し、全硬度を決定する。

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.

安全上の警告

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

必要な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)

器具

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

手順

1

Pipette exactly 25.0 mL of the water sample into the Erlenmeyer flask.

2 分
2

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

1 分 Ammonia odor — work in ventilated area
3

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

1 分
4

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

3 分
5

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

10 分
6

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

5 分
7

Record the final volume. Repeat for concordant results.

12 分
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

予想される結果

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.

後片付け

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

詳細

カテゴリ
Titrations
難易度
Advanced (University)
所要時間
45 分
推定費用
$15.00
ステップ数
8
材料
5

その他の実験

pH滴定曲線 50 min フェノールフタレインを用いた酸塩基滴定 45 min メチルオレンジを用いた酸塩基滴定 40 min ヨウ素によるビタミンC滴定 40 min 二重指示薬による炭酸塩・重炭酸塩混合物の滴定 55 min 制酸剤錠剤の逆滴定 60 min 沈殿滴定（モール法） 45 min 漂白剤のヨウ素滴定 50 min 過マンガン酸カリウムによる酸化還元滴定 50 min 電導度滴定 50 min

Frequently Asked Questions

What is the objective of EDTA錯体滴定による水の硬度測定?
エリオクロムブラックTを指示薬として用い、EDTAで水試料中のCa²⁺とMg²⁺イオンを滴定し、全硬度を決定する。
How difficult is EDTA錯体滴定による水の硬度測定?
This experiment is rated as Advanced (University). It takes approximately 45 minutes to complete.
What safety precautions are needed for EDTA錯体滴定による水の硬度測定?
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錯体滴定による水の硬度測定?
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錯体滴定による水の硬度測定?
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.