Test de Dureté de l'Eau avec une Solution Savonneuse

Comparaison de la dureté de l'eau en mesurant la formation de mousse de savon

Qualitative Analysis Beginner (Middle School) 40 min ~$6,00

Objectif

Déterminer la dureté relative d'échantillons d'eau en mesurant le volume de solution savonneuse nécessaire pour produire une mousse durable.

Contexte

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.

Avertissements de sécurité

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

EPI requis

goggles lab_coat

Matériaux

  • 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

Équipement

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

Procédure

1

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

5 min
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 min
3

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

20 min
4

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

5 min
5

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

5 min

Résultats attendus

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.

Nettoyage

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

Détails

Catégorie
Qualitative Analysis
Difficulté
Beginner (Middle School)
Durée
40 min
Coût estimé
$6,00
Étapes
5
Matériaux
6

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Frequently Asked Questions

What is the objective of Test de Dureté de l'Eau avec une Solution Savonneuse?
Déterminer la dureté relative d'échantillons d'eau en mesurant le volume de solution savonneuse nécessaire pour produire une mousse durable.
How difficult is Test de Dureté de l'Eau avec une Solution Savonneuse?
This experiment is rated as Beginner (Middle School). It takes approximately 40 minutes to complete.
What safety precautions are needed for Test de Dureté de l'Eau avec une Solution Savonneuse?
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 Test de Dureté de l'Eau avec une Solution Savonneuse?
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 Test de Dureté de l'Eau avec une Solution Savonneuse?
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.