JEE Main 2018ChemistryChemical EquilibriumMediumMCQ

JEE Main 2018 — Chemical Equilibrium Question with Solution

JEE Main 2018 (08 Apr)

Question

An aqueous solution contains  0.10 M H2S and 0.20 M HCl. If the equilibrium constant for the formation of HS- from H2S is 1.0×10-7 and that of S2- from HS- ions is 1.2×10-13, then, the concentration of S2- ions in the aqueous solution is:

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Show full solutionCorrect option: C
Correct answer
C3×10-20

Step-by-step explanation

HCl→H++Cl-0.2+x+y0.2

H2S⇌H++HS-0.1-x0.2+x+yx-y; Ka1=10-7

HS-→H++S2-x-y0.2+x+yy; Ka2=1.2×10-13

 

H+=0.2+x+yM=0.2M

Ka1=H+HS-H2S=0.2×HS-0.1-x=0.2HS-0.1           (x=negligible)

HS-=Ka1×0.10.2=12×10-7

Ka2=H+S2-HS-=0.2 MS2-12×10-7

S2-=Ka2×12×10-70.2=1.2×10-13×12×10-70.2=3×10-20 M
 

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About this question

This is a previous-year question from JEE Main 2018, covering the Chemical Equilibrium chapter of Chemistry. PrepSharp catalogues every PYQ from JEE Main with a verified answer key and step-by-step solution prepared by IIT alumni — so you can search by chapter, topic or year and revise efficiently.