肥皂液硬水测试

通过测量皂沫形成量比较水的硬度

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

目标

通过测量产生持续皂沫所需的肥皂溶液体积，测定水样的相对硬度。

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.

安全警告

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

所需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

设备

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

步骤

1

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

5 分钟
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 分钟
3

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

20 分钟
4

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

5 分钟
5

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

5 分钟

预期结果

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.

清理

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

详情

类别
Qualitative Analysis
难度
Beginner (Middle School)
时长
40 分钟
预估费用
$6.00
步骤数
5
材料
6

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Frequently Asked Questions

What is the objective of 肥皂液硬水测试?
通过测量产生持续皂沫所需的肥皂溶液体积，测定水样的相对硬度。
How difficult is 肥皂液硬水测试?
This experiment is rated as Beginner (Middle School). It takes approximately 40 minutes to complete.
What safety precautions are needed for 肥皂液硬水测试?
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 肥皂液硬水测试?
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 肥皂液硬水测试?
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.