What would be the molality of 20% (mass/mass) aqueous solution of KI ?
Molar mass of KI is 166gmol−1
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JEE MAIN 2019
A
1.51
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B
1.35
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C
1.08
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D
1.48
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Solution
The correct option is A1.51 20% (mass/mass) aqueous solution of KI means 20g of KI in 100g of solution.
Mass of solution =100g
Mass of solute=20g
Mass of solvent=mass of solution - mass of solute =(100−20)g=80g=0.08kg
Molar mass of KI is 166gmol−1 Number of moles of solute (n)=mass of KImolar mass of KI=20166=0.121mol
So, molality of solution m=number of moles of soluteweight of solvent (in kg) ⇒m=0.1210.08=1.51mol/kg
Hence, option (A) is the correct.