Chem 14A Freezing Point Depression Name:Samantha dela Molar Mass Determination u

Question

Chem 14A Freezing Point Depression Name:Samantha dela Molar Mass Determination using Freezing Point Depression Data Sheet Molar Mass Determinsinaaarc Part A: Freezing Point Determination of the Pure Solvent Mass of the empty test tube and beaker, Mass of the test tube and beaker with cyclohexane: 2 ru ·e13 HS Trial 1 Trial 2 Trial 3 Freezing point temperature: 78e.2t 63 s243--8- Averagofreezing point: 8 Mass of the unknown:C319 3. Part B: Freezing Point Determination of the Solution Trial 1 Trial 2 Trial 3 2. Freezing point temperature:25 Average freezing point: Results: Determination of the Molar Mass Mass of the cyclohexane: li dSI 3.2- a.6 .3 82.qug-.8=ll'131 The freezing point depression constant Kf for cyclohexane is 20.2 ° C/m. Molality of the unknown nonelectrolyte Moles of the unknown nonelectrolyte: Molar Mass of the unknown nonelectrolyte Unknown Number

Explanation / Answer

According to data sheet;

The freezing point of cyclohexane is 8.1

Mass of cyclohexane = 11.131 g

Kf fro cyclo hexane = 20.2 C/m

Freezing point of solution = 3.2 C

Freezing point depression.= TF(puresolvent) TF(solution).

= 8.1 – 3.2

= 4.9 C

For non –electrolytes i = 1

Tf= ikfm

4.9 = 1* 20.2 *m

m , molatity = 0.2436 Mole / kg

number of moles = m* kg solvent

= 0.2436 Mole / kg /11.131 /1000 kg

= 0.0027 moles of solute

Amount of solute 0.347 g

Molar mass= amount in g / number of moles

= 0.347 g/ 0.0027 mole

= 128.52 g/ mole

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