COMEDK 2024 Shift 2 Paper

Let's solve the problem step-by-step to find the percentage of element X and the formula of the violet-colored compound formed when the Lassaigne's extract of the organic compound is treated with sodium nitroprusside.
First, we'll calculate the percentage of the element X in the organic compound based on the mass of barium sulphate (BaSO4) precipitated.
The molecular weight of barium sulphate, BaSO4, is:
Molecular weight of BaSO4=137+32+64=233g∕mol
The atomic weight of sulphur (S) is 32g∕mol. When barium sulphate is formed, one mole of BaSO4 contains one mole of sulphur:
Moles of BaSO4 formed = Mass of BaSO4∕ Molecular weight of BaSO4 :
Moles of BaSO4=‌

1.2g

233g∕mol

=‌

1.2

233

≈0.00515‌mol
Moles of sulphur = Moles of BaSO4=0.00515‌mol
The mass of sulphur in the compound is then:
Mass of sulphur = Moles of sulphur × Atomic weight of sulphur =0.00515‌mol×32g∕mol=0.1648g
Now, the percentage of element X (sulphur in this case) in the organic compound is:
So, the percentage of element X is 20.6%.
Next, we need to determine the formula of the violet-colored compound formed when Lassaigne's extract is treated with sodium nitroprusside. The violet coloration is characteristic of the reaction between sodium nitroprusside and sulphur in the extract.
The chemical formula for the violet-colored compound formed in this reaction is:
Na4[Fe(CN)5‌NOS]
Thus, the correct answer is:
Option B
20.6‌‌&‌‌Na4[Fe(CN)5‌NOS]