Bacterial Contamination in Drinking Water Test Using Sulphide Ion Method

Chemistry Project: Detecting Water Pollution Using Hydrogen Sulphide Test

📘 CHEMISTRY INVESTIGATORY PROJECT

CHECKING THE BACTERIAL CONTAMINATION IN DRINKING WATER BY TESTING SULPHIDE ION

🧾 COVER PAGE

CHEMISTRY INVESTIGATORY PROJECT
ON

“Checking the Bacterial Contamination in Drinking Water by Testing Sulphide Ion”

Submitted By:
Name: ____________
Class: XI
Roll No.: ____________
School: ____________
Session: ____________

Submitted To:
Chemistry Teacher: ____________

🏫 CERTIFICATE

This is to certify that ____________ of Class XI has successfully completed the Chemistry Investigatory Project titled “Checking the Bacterial Contamination in Drinking Water by Testing Sulphide Ion” under the guidance of the Chemistry teacher during the academic session ____________.

Teacher's Signature: ____________
Examiner's Signature: ____________
Date: ____________

🙏 ACKNOWLEDGEMENT

I express my sincere gratitude to my Chemistry teacher for valuable guidance and constant support throughout this project. I am also thankful to the laboratory staff for providing necessary chemicals and apparatus. Their help made this investigation successful.

📑 INDEX

  1. Introduction
  2. Aim
  3. Theory
  4. Materials Required
  5. Procedure
  6. Observation Table
  7. Calculations
  8. Result
  9. Conclusion
  10. Precautions
  11. Research and Experimentation
  12. Analysis
  13. Limitation of Study
  14. Bibliography

1. INTRODUCTION

Clean drinking water is essential for human health. However, water can get contaminated by microorganisms and bacteria due to sewage, waste disposal, and decaying organic matter.

Certain bacteria reduce sulphates in water to form hydrogen sulphide (H₂S) gas, which indicates contamination. This gas has a characteristic foul smell similar to rotten eggs.

Thus, detection of sulphide ions indirectly helps in identifying bacterial contamination in water samples.

2. AIM

To check and compare bacterial contamination in different drinking water samples by testing the presence of sulphide ions.

3. THEORY

Certain anaerobic bacteria reduce sulphate ions (SO₄²⁻) present in water into sulphide ions (S²⁻), forming hydrogen sulphide gas:

SO₄²⁻ → S²⁻ → H₂S (gas)

Hydrogen sulphide reacts with lead acetate paper to form black lead sulphide:

Pb(CH₃COO)₂ + H₂S → PbS (black precipitate) + 2CH₃COOH

The intensity of blackening indicates the level of bacterial contamination.

4. MATERIALS REQUIRED

  • Different water samples (tap water, river water, bottled water, pond water)
  • Lead acetate paper strips
  • Test tubes
  • Dropper
  • Cotton plugs
  • Conical flasks
  • Distilled water
  • Incubator or warm place

5. PROCEDURE

A labeled chemistry laboratory setup showing four test tubes (A, B, C, D) containing different water samples. Each test tube is closed with a cork holding a strip of lead acetate paper inside. The paper shows varying degrees of blackening depending on sulphide ion presence. The test tubes are arranged in a stand on a laboratory bench, representing a school-level experiment for detecting bacterial contamination in water.
Experimental setup for detection of bacterial contamination in drinking water using sulphide ion (lead acetate paper test).


(A) Preparation of Samples

  1. Collect different water samples in clean bottles.
  2. Label them properly as A, B, C, D.

(B) Sulphide Ion Test

  1. Take each water sample in a test tube.
  2. Suspend a strip of lead acetate paper at the mouth of the test tube using a cork.
  3. Keep the setup in a warm place for 24–48 hours.
  4. Observe any colour change on the paper.
  5. Repeat for all samples.

6. OBSERVATION TABLE

A bar chart comparing contamination levels in four water samples: Bottled Water, Tap Water, River Water, and Pond Water. The x-axis represents sample types and the y-axis shows relative contamination levels from 0 to 10. Bottled water shows the lowest bar, while pond water shows the highest bar. The chart is color-coded and includes data labels on each bar, illustrating increasing contamination from treated to natural water sources.
Bar graph showing comparison of bacterial contamination levels in different drinking water samples based on sulphide ion test.


Water Sample Source Colour Change on Lead Acetate Paper Level of Contamination
A Tap Water Slight blackening Low
B Bottled Water No change Very Low
C River Water Moderate blackening High
D Pond Water Strong blackening Very High

7. CALCULATIONS

(No numerical calculations required)

Contamination level is determined qualitatively based on intensity of black precipitate formation.

  • No blackening → No sulphide → Clean water
  • Light blackening → Low contamination
  • Dark blackening → High bacterial contamination

8. RESULT

Pond water showed the highest bacterial contamination, while bottled water showed the least or negligible contamination.

9. CONCLUSION

The presence of sulphide ions indicates bacterial activity in water. Among the tested samples, natural water sources such as ponds and rivers show higher contamination compared to treated drinking water.

10. PRECAUTIONS

  • Use clean and sterilized test tubes
  • Avoid touching lead acetate paper directly
  • Seal test tubes properly
  • Keep samples in a warm environment for better reaction
  • Do not inhale any gas produced
  • Handle chemicals carefully

11. RESEARCH AND EXPERIMENTATION

This experiment is based on the principle that anaerobic bacteria produce hydrogen sulphide gas by reducing sulphates in water. Lead acetate paper acts as an indicator for detecting sulphide ions.

12. ANALYSIS

Water samples from natural sources showed higher sulphide formation due to presence of organic waste and microbial activity. Treated water samples showed little or no reaction due to purification processes like filtration and chlorination.

13. LIMITATION OF THE STUDY

  • Only qualitative analysis is possible
  • Exact bacterial count cannot be determined
  • Environmental conditions may affect results
  • Lead acetate test may not detect all types of contamination
  • Limited number of samples tested

14. BIBLIOGRAPHY

  • NCERT Chemistry Lab Manual Class XI
  • NCERT Chemistry Textbook Class XI
  • Modern ABC of Chemistry
  • Practical Chemistry by O.P. Pandey
  • Standard Laboratory Handbook
INTERNAL LINKS  
/chemistry-projects/class-11-water-contamination-test
/science-experiments/sulphide-ion-test-method
/water-quality-analysis-school-projects
/chemistry-lab-experiments/lead-acetate-test
/environmental-science-projects/water-pollution-study
/class-11-chemistry-investigatory-projects

❓ FAQs – Checking Bacterial Contamination in Drinking Water (Sulphide Ion Test)

1. What is the purpose of testing sulphide ions in water?

Testing sulphide ions helps detect the presence of hydrogen sulphide gas, which is often produced by bacteria in contaminated water. It is an indirect method to check bacterial contamination.

2. How does sulphide indicate bacterial contamination?

Certain anaerobic bacteria break down sulphates in water and produce hydrogen sulphide (H₂S) gas. This gas reacts with lead acetate paper, showing blackening, which indicates contamination.

3. What is the chemical used to detect sulphide ions?

Lead acetate paper is commonly used. It reacts with hydrogen sulphide gas to form black lead sulphide (PbS).

4. Which water sample is usually most contaminated?

Natural water sources like pond water or river water are usually more contaminated compared to treated tap or bottled water.

5. What does blackening of lead acetate paper mean?

Blackening indicates the formation of lead sulphide (PbS), which confirms the presence of hydrogen sulphide gas and bacterial activity.

6. Is this test qualitative or quantitative?

This test is qualitative, meaning it shows presence or absence of contamination but does not measure exact bacterial count.

7. Why is distilled water used in experiments?

Distilled water is free from impurities and microorganisms, so it is used for preparing controls and accurate comparisons.

8. What are the limitations of this method?

It cannot detect all types of bacteria, gives only approximate results, and may be affected by environmental conditions.

9. Why is hydrogen sulphide gas produced in contaminated water?

It is produced when anaerobic bacteria break down sulphur-containing compounds in water under low oxygen conditions.

10. Is drinking water always free from bacteria?

No, even drinking water can have minimal microbial contamination, but treated water is made safe through filtration and disinfection.


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