🔬 Limit Test of Sulphide

🎯 Aim

To perform the limit test for sulphide in a given sample and compare it with the standard solution.

🧪 Principle

Sulphide ions react with lead acetate paper to produce a black or brown stain of lead sulphide (PbS).

Intensity of stain ∝ amount of sulphide present

If test solution का stain standard से darker नहीं है, sample passes the test ✅

⚗️ Chemical Reaction

S²⁻  +  Pb²⁺  →  PbS ↓ (Black precipitate)

🧰 Apparatus

• Nessler cylinders (2)

• Lead acetate paper

• Measuring cylinder

• Test tubes

• Glass rod

🧴 Reagents

• Test solution

• Standard sulphide solution

• Lead acetate paper

• Dilute acid (if required)

🧑‍🔬 Procedure

1. Take equal volume of test solution in one Nessler cylinder

2. Take standard sulphide solution in another cylinder

3. Suspend lead acetate paper above both cylinders

4. Close the setup and allow reaction for specified time

5. Compare colour/stain intensity

👀 Observation

Solution	Colour / Stain
Standard	Light brown/black
Test	…………………

✅ Result

• If test stain ≤ standard stain → PASS

• If test stain > standard stain → FAIL

📘 Viva Voce (Exam-Oriented)

1. Why is sulphide impurity harmful?

2. Which reagent is used for detection of sulphide?

3. What colour is produced in sulphide limit test?

4. Why lead acetate paper is used?

5. Principle of limit test of sulphide?

🧠 Exam Writing Tip

“Limit test of sulphide is based on the formation of lead sulphide which produces a dark stain on lead acetate paper.”

🔗 Related Practical Blogs

• ✔ Limit Test of Chloride

• ✔ Limit Test of Iron

• ✔ Limit Test of Heavy Metals

• ✔ Limit Test of Arsenic

• ✔ Limit Test of Nitrate

🚀 Coming Next in Limit Test Series

👉 Limit Test of Calcium

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