石けん液による硬水試験

石けんの泡立ちを測定して水の硬度を比較する

Qualitative Analysis Beginner (Middle School) 40 分 ~$6.00

目的

持続する泡立ちを生じるのに必要な石けん溶液の量を測定することで、水試料の相対的な硬度を決定する。

背景

Hard water contains dissolved calcium and magnesium ions (Ca²⁺, Mg²⁺) that react with soap (sodium stearate) to form an insoluble scum before lather can form. By titrating water samples with a standard soap solution and counting the number of drops needed for a persistent lather, students can rank water hardness and understand the concept of temporary vs. permanent hardness.

安全上の警告

  • Soap solution may irritate eyes
  • Ensure stoppers are secure before shaking
  • Let boiled water cool before handling

必要なPPE

goggles lab_coat

材料

  • Soap solution (standard) (50 mL)
    Liquid castile soap diluted 1:10
  • Distilled water (50 mL)
    Control (soft water)
  • Tap water (50 mL)
    Unknown hardness
  • Mineral water (50 mL)
    Known mineral content
  • Calcium chloride solution (0.01M) (50 mL)
    Simulated hard water
  • Boiled tap water (50 mL)
    Temporary hardness removed

器具

Stoppered test tubes or small bottles (6) Dropper pipette (calibrated) Measuring cylinder (10 mL) Marker pen

手順

1

Label 6 test tubes: distilled, tap, mineral, CaCl₂, boiled tap. Add 10 mL of each water sample.

5 分
2

Add soap solution one drop at a time to the distilled water. After each drop, stopper and shake vigorously for 10 seconds. Count drops until a lather persists for 30 seconds.

5 分
3

Repeat Step 2 for each water sample, recording the number of drops needed for persistent lather.

20 分
4

Compare results: rank samples from softest (fewest drops) to hardest (most drops).

5 分
5

Compare boiled tap water to unboiled tap water. The difference indicates temporary hardness (from Ca(HCO₃)₂).

5 分

予想される結果

Distilled water requires the fewest drops of soap. CaCl₂ solution requires the most. Boiled tap water should require fewer drops than unboiled tap water, demonstrating removal of temporary hardness.

後片付け

Pour soapy water down the drain with running water. Rinse all test tubes and stoppers.

詳細

カテゴリ
Qualitative Analysis
難易度
Beginner (Middle School)
所要時間
40 分
推定費用
$6.00
ステップ数
5
材料
6

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Frequently Asked Questions

What is the objective of 石けん液による硬水試験?
持続する泡立ちを生じるのに必要な石けん溶液の量を測定することで、水試料の相対的な硬度を決定する。
How difficult is 石けん液による硬水試験?
This experiment is rated as Beginner (Middle School). It takes approximately 40 minutes to complete.
What safety precautions are needed for 石けん液による硬水試験?
Key safety precautions include: Soap solution may irritate eyes; Ensure stoppers are secure before shaking; Let boiled water cool before handling.
What materials are needed for 石けん液による硬水試験?
The main materials required are: Soap solution (standard), Distilled water, Tap water, Mineral water, Calcium chloride solution (0.01M).
What results should I expect from 石けん液による硬水試験?
Distilled water requires the fewest drops of soap. CaCl₂ solution requires the most. Boiled tap water should require fewer drops than unboiled tap water, demonstrating removal of temporary hardness.