JEE Main 2019ChemistrySolutionsMediumMCQ

JEE Main 2019 — Solutions Question with Solution

JEE Main 2019 (12 Jan Shift 2)

Question

Molecules of benzoic acid C6H5COOH dimerise in 30 g of benzene. ' w ' g of benzoic acid shows a depression in freezing point equal to 2 K. If the percentage association of the acid to form dimer in the solution is 80, then w is: ( Given that Kf=5 Kmol-1, molar mass of benzoic acid =122 gmol-1)

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Show full solutionCorrect option: B
Correct answer
B2.4 g

Step-by-step explanation

ΔTf =kf×m×i …(i)

Molecular weight of C6H5COOH=112

n = 2  because benzoic acid is dimerised, β = 80 % = 0.8  

Here i=1n-1β+1

i=12-1 0.8+1

=0.6

Put the value in equation (i)

2=0.6×wt.of benzoic acid112301000×5

weight  of benzoic acid =2.4 g

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About this question

This is a previous-year question from JEE Main 2019, covering the Solutions 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.