Chemistry Practice Problems Freezing Point Depression Practice Problems Solution: Nicotine, extracted from tobacco leaves, is a liqu...

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Solution: Nicotine, extracted from tobacco leaves, is a liquid completely miscible with water at temperatures below  60°C. What is the molality of nicotine (a covalent substance) in an aqueous solution that starts to freeze at -0.450°C? (Note that the Kf for water is 1.86 °C m -1)a) 2.42b) 0.0336c) 4.13d) 29.7e) 0.242 

Problem

Nicotine, extracted from tobacco leaves, is a liquid completely miscible with water at temperatures below  60°C. What is the molality of nicotine (a covalent substance) in an aqueous solution that starts to freeze at -0.450°C? (Note that the Kf for water is 1.86 °C m -1)

a) 2.42

b) 0.0336

c) 4.13

d) 29.7

e) 0.242

 

Solution

We’re being asked to find the molality of a solution when nicotine is dissolved in water. When calculating the freezing point of a solution, we’re going to use the equation for Freezing Point Depression.


∆Tf = change in freezing point = Tf pure solvent –Tf solution
Kf = freezing point depression constant
i = van' t Hoff factor of the solute = no. of ions
m = molality


Determine the required values for the Freezing Point Depression equation:

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