Which of the following is/are the test used for detection of sulphur ?
Which of the following is/are the test used for detection of sulphur ?
The correct option is C Both A and B
The presence of sulphur in the
organic compound can be detected by the following tests:
Oxidation Test:
The organic compound
is fused with a mixture of potassium nitrate and sodium carbonate. Sulphur, if
present, gets oxidised to sodium sulphate.
3KNO3⟶3KNO2+3[O]Na2CO3+S+3[O]⟶Na2SO4+CO2
The fused mass is extracted
with water, the contents are boiled and filtered. The filtrate contains sodium
sulphate. The filtrate is acidified with dilute hydrochloric acid and a
solution of barium chloride is added. Formation of a white precipitate
indicates the presence of sulphur.
BaCl2+Na2SO4⟶BaSO4↓+2NaCl
Lassaigne’s Test:
A small piece of a sodium
metal is heated gently in a fusion tube till it melts to a shining globule. At
this stage, a small amount of substance is added and the tube is heated
strongly. The red hot tube is plunged into distilled water contained in a china
dish. The contents are boiled for some time, cooled and then filtered. The filtrate
is known as sodium extract or Lassaigne ‘s extract.
The extract contains sodium
sulphide formed by the reaction between sulphur (present in the compound) and
sodium:
2Na+S⟶Na2S
The Lassaigne’s extract is
divided into two parts and following tests are performed:
Lead acetate test: One part of
the extract is acidified with acetic acid and then lead acetate solution is
added. Formation of a black precipitate confirms the presence of sulphur in the
organic compound.
Na2S+Pb(CH3COO)2⟶PbS↓+2CH3COONa
Sodium nitroprusside test. A
few drops of sodium nitroprusside solution are added to another part of the
Lassaigne’s extract. The appearance of purple colouration confirms the presence
of sulphur:
Na2S+Na2[Fe(CN)5NO]⟶Na4[Fe(CN)5NO.S]
The presence of sulphur in the organic compound can be detected by the following tests:
Oxidation Test:
The organic compound is fused with a mixture of potassium nitrate and sodium carbonate. Sulphur, if present, gets oxidised to sodium sulphate.
3KNO3⟶3KNO2+3[O]Na2CO3+S+3[O]⟶Na2SO4+CO2
The fused mass is extracted with water, the contents are boiled and filtered. The filtrate contains sodium sulphate. The filtrate is acidified with dilute hydrochloric acid and a solution of barium chloride is added. Formation of a white precipitate indicates the presence of sulphur.
BaCl2+Na2SO4⟶BaSO4↓+2NaCl
Lassaigne’s Test:
A small piece of a sodium metal is heated gently in a fusion tube till it melts to a shining globule. At this stage, a small amount of substance is added and the tube is heated strongly. The red hot tube is plunged into distilled water contained in a china dish. The contents are boiled for some time, cooled and then filtered. The filtrate is known as sodium extract or Lassaigne ‘s extract.
The extract contains sodium sulphide formed by the reaction between sulphur (present in the compound) and sodium:
2Na+S⟶Na2S
The Lassaigne’s extract is divided into two parts and following tests are performed:
Lead acetate test: One part of the extract is acidified with acetic acid and then lead acetate solution is added. Formation of a black precipitate confirms the presence of sulphur in the organic compound.
Na2S+Pb(CH3COO)2⟶PbS↓+2CH3COONa
Sodium nitroprusside test. A few drops of sodium nitroprusside solution are added to another part of the Lassaigne’s extract. The appearance of purple colouration confirms the presence of sulphur:
Na2S+Na2[Fe(CN)5NO]⟶Na4[Fe(CN)5NO.S]
