Teste de Dureza da Água com Solução de Sabão

Comparação da dureza da água medindo a formação de espuma de sabão

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

Objetivo

Determinar a dureza relativa de amostras de água medindo o volume de solução de sabão necessário para produzir uma espuma duradoura.

Contexto

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.

Avisos de segurança

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

EPI necessário

goggles lab_coat

Materiais

  • 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

Equipamentos

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

Procedimento

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

Resultados esperados

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.

Limpeza

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

Detalhes

Categoria
Qualitative Analysis
Dificuldade
Beginner (Middle School)
Duração
40 min
Custo estimado
$6,00
Passos
5
Materiais
6

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Frequently Asked Questions

What is the objective of Teste de Dureza da Água com Solução de Sabão?
Determinar a dureza relativa de amostras de água medindo o volume de solução de sabão necessário para produzir uma espuma duradoura.
How difficult is Teste de Dureza da Água com Solução de Sabão?
This experiment is rated as Beginner (Middle School). It takes approximately 40 minutes to complete.
What safety precautions are needed for Teste de Dureza da Água com Solução de Sabão?
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 Teste de Dureza da Água com Solução de Sabão?
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 Teste de Dureza da Água com Solução de Sabão?
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.