# When 14.3 g of a certain molecular compound X are dissolved in 85.0 g of benzene C6H6, the freezing point of the solution is measured to be 0.5 °C. Calculate the molar mass of X. molal freezing point depression constant (Kf)°C·kg·mol−1 of benzen is 5.07 If you need any additional information on benzene, use only what you find in the ALEKS Data resource. Also, be sure your answer has a unit symbol, and is rounded to 2 significant digits.

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When 14.3 g of a certain molecular compound X are dissolved in

85.0 g of benzene C6H6, the freezing point of the solution is measured to be 0.5 °C. Calculate the molar mass of X.

molal freezing point depression constant (Kf)
°C·kg·mol−1 of benzen is 5.07

If you need any additional information on benzene, use only what you find in the ALEKS Data resource. Also, be sure your answer has a unit symbol, and is rounded to

2

significant digits.

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Step 1

The depression in the freezing point refers to a phenomenon which is used to describe the effect of addition of solute to a given solvent that results in the lowering of the freezing point of the solvent. The formula is as follows: help_outlineImage TranscriptioncloseAT,=K¢m AT, is the depression in freezing point K is the freezing point molar constant of solvent m is the molality of the solution Number of moles of solute m=- Mass of solvent in kg fullscreen
Step 2

In the given problem, the mass of solute X is given to be 14.3 g.

The mass of solvent benzene is given to be 85 g=0.085 kg.

The molal freezing point depression constant is given to be 5.07 oC kg mol-1.

The freezing point of the solution is given to be 0.5 0C.

The freezing point of pure benzene is 5.5oC.

The depression in freezing point can be calculated as follows:

Step 3

The molar mass of compound X can ... help_outlineImage TranscriptioncloseAT =K2m Mass of solute 5°C=5.07°C.kg.molax. Molar mass of solute Mass of solvent (in kg) 14.3g =5.07°C.kg.mol Molar mass of solute 0.085 kg 14.3g 5°CX0.085 kg Molar mass of solute=5.07°C.kg.mol1x- -170.590 g/mol fullscreen

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