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A sample of domestic sewage is digested with silver sulphate, sulphuric acid, potassium dichromate and mercuric sulphate in chemical oxygen demand (COD) test. The digested sample is then titrated with standard ferrous ammonium sulphate (FAS) to determine the un-reacted amount of
- a)mercuric sulphate
- b)potassium dichromate
- c)silver sulphate
- d)sulphuric acid
Correct answer is option 'B'. Can you explain this answer?
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A sample of domestic sewage is digested with silver sulphate, sulphuri...
Explanation:
The chemical oxygen demand (COD) test is used to determine the amount of organic pollutants in water or wastewater. In this test, the sample is digested with various chemicals to oxidize the organic compounds present. The un-reacted amount of these chemicals can then be determined by titration with a standard solution.
In this question, the sample of domestic sewage is digested with silver sulphate, sulphuric acid, potassium dichromate, and mercuric sulphate. The digested sample is then titrated with standard ferrous ammonium sulphate (FAS) to determine the un-reacted amount of each chemical.
To determine the un-reacted amount of each chemical, we need to consider the reactions that take place during the digestion process:
1. Silver sulphate (Ag2SO4):
- Ag2SO4 + 2H2SO4 → 2Ag+ + SO4^2- + 2H2O
The silver sulphate is reduced to silver ions (Ag+).
2. Sulphuric acid (H2SO4):
- H2SO4 → 2H+ + SO4^2-
The sulphuric acid dissociates into hydrogen ions (H+) and sulphate ions (SO4^2-).
3. Potassium dichromate (K2Cr2O7):
- K2Cr2O7 + 8H2SO4 → 2K+ + Cr2(SO4)3 + 7H2O + 3[O]
The potassium dichromate is reduced to chromium sulfate and water, releasing oxygen.
4. Mercuric sulphate (HgSO4):
- HgSO4 + 2H2SO4 → Hg2+ + SO4^2- + 2H2O
The mercuric sulphate is reduced to mercury ions (Hg2+).
During the titration with FAS, the un-reacted amount of each chemical can be determined by measuring the amount of FAS required to react with them. The FAS reacts with the un-reacted chemicals as follows:
1. Un-reacted mercuric sulphate:
- Hg2+ + 2Fe(NH4)2(SO4)2 → Hg2[Fe(NH4)2(SO4)2]2 + 2NH4+ + 2SO4^2-
The un-reacted mercuric sulphate reacts with the FAS to form a complex.
2. Un-reacted potassium dichromate:
- Cr2(SO4)3 + 6Fe(NH4)2(SO4)2 → 2Cr[Fe(NH4)2(SO4)2]3 + 6NH4+ + 6SO4^2-
The un-reacted potassium dichromate reacts with the FAS to form a complex.
3. Un-reacted silver sulphate and sulphuric acid:
- These do not react with FAS and do not contribute to the titration.
Therefore, the un-reacted amount of potassium dichromate can be determined by titrating the digested sample with FAS. The other chemicals (silver sulphate, sulphuric acid, and mercuric sulphate) do not react with FAS and
The chemical oxygen demand (COD) test is used to determine the amount of organic pollutants in water or wastewater. In this test, the sample is digested with various chemicals to oxidize the organic compounds present. The un-reacted amount of these chemicals can then be determined by titration with a standard solution.
In this question, the sample of domestic sewage is digested with silver sulphate, sulphuric acid, potassium dichromate, and mercuric sulphate. The digested sample is then titrated with standard ferrous ammonium sulphate (FAS) to determine the un-reacted amount of each chemical.
To determine the un-reacted amount of each chemical, we need to consider the reactions that take place during the digestion process:
1. Silver sulphate (Ag2SO4):
- Ag2SO4 + 2H2SO4 → 2Ag+ + SO4^2- + 2H2O
The silver sulphate is reduced to silver ions (Ag+).
2. Sulphuric acid (H2SO4):
- H2SO4 → 2H+ + SO4^2-
The sulphuric acid dissociates into hydrogen ions (H+) and sulphate ions (SO4^2-).
3. Potassium dichromate (K2Cr2O7):
- K2Cr2O7 + 8H2SO4 → 2K+ + Cr2(SO4)3 + 7H2O + 3[O]
The potassium dichromate is reduced to chromium sulfate and water, releasing oxygen.
4. Mercuric sulphate (HgSO4):
- HgSO4 + 2H2SO4 → Hg2+ + SO4^2- + 2H2O
The mercuric sulphate is reduced to mercury ions (Hg2+).
During the titration with FAS, the un-reacted amount of each chemical can be determined by measuring the amount of FAS required to react with them. The FAS reacts with the un-reacted chemicals as follows:
1. Un-reacted mercuric sulphate:
- Hg2+ + 2Fe(NH4)2(SO4)2 → Hg2[Fe(NH4)2(SO4)2]2 + 2NH4+ + 2SO4^2-
The un-reacted mercuric sulphate reacts with the FAS to form a complex.
2. Un-reacted potassium dichromate:
- Cr2(SO4)3 + 6Fe(NH4)2(SO4)2 → 2Cr[Fe(NH4)2(SO4)2]3 + 6NH4+ + 6SO4^2-
The un-reacted potassium dichromate reacts with the FAS to form a complex.
3. Un-reacted silver sulphate and sulphuric acid:
- These do not react with FAS and do not contribute to the titration.
Therefore, the un-reacted amount of potassium dichromate can be determined by titrating the digested sample with FAS. The other chemicals (silver sulphate, sulphuric acid, and mercuric sulphate) do not react with FAS and
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A sample of domestic sewage is digested with silver sulphate, sulphuric acid, potassium dichromate and mercuric sulphate in chemical oxygen demand (COD) test. The digested sample is then titrated with standard ferrous ammonium sulphate (FAS) to determine the un-reacted amount ofa)mercuric sulphateb)potassium dichromatec)silver sulphated)sulphuric acidCorrect answer is option 'B'. Can you explain this answer?
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A sample of domestic sewage is digested with silver sulphate, sulphuric acid, potassium dichromate and mercuric sulphate in chemical oxygen demand (COD) test. The digested sample is then titrated with standard ferrous ammonium sulphate (FAS) to determine the un-reacted amount ofa)mercuric sulphateb)potassium dichromatec)silver sulphated)sulphuric acidCorrect answer is option 'B'. Can you explain this answer? for GATE 2025 is part of GATE preparation. The Question and answers have been prepared according to the GATE exam syllabus. Information about A sample of domestic sewage is digested with silver sulphate, sulphuric acid, potassium dichromate and mercuric sulphate in chemical oxygen demand (COD) test. The digested sample is then titrated with standard ferrous ammonium sulphate (FAS) to determine the un-reacted amount ofa)mercuric sulphateb)potassium dichromatec)silver sulphated)sulphuric acidCorrect answer is option 'B'. Can you explain this answer? covers all topics & solutions for GATE 2025 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for A sample of domestic sewage is digested with silver sulphate, sulphuric acid, potassium dichromate and mercuric sulphate in chemical oxygen demand (COD) test. The digested sample is then titrated with standard ferrous ammonium sulphate (FAS) to determine the un-reacted amount ofa)mercuric sulphateb)potassium dichromatec)silver sulphated)sulphuric acidCorrect answer is option 'B'. Can you explain this answer?.
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