Determination of the Molecular Weight of an Unknown Non

Determination of the Molecular Weight of an Unknown Non -...

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Determination of the Molecular Weight of an Unknown Non-Electrolyte by its Effect on the Freezing Point Depression in t-Butyl Alcohol Olivia Downs 2/21/11 CHM 1046L / #85606 Megan Conkling & Chris Reyes
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The purpose of this experiment was to determine the molecular weight of the unknown electrolyte by finding its’ freezing point depression in t-Butyl alcohol. The freezing point was depressed because it is lower than the freezing point of a pure solvent. Freezing points are caused to be depressed if the solution is high in concentration. The molecular weight was calculated using freezing point depression through a series of equations. First, the molality (Moles solute ÷ kg solvent) was found. In this experiment, molality can also be expressed as: m= ΔT ÷ fkrp. To find the molecular weight of a solution, the equation is: MW= g solute ÷ moles solute. To find the moles solute, this equation can be used: Moles solute= (ΔT) × (kg solvent) ÷ (kf). The kf is the molal freezing point depression constant which is always: 8.37◦C/m. Before solving for the molecular weight, the grams of solute was found by taking the volume in milliliters of the unknown added and multiplying that volume by the density of the unknown(D=m ÷ v). After the grams solute is calculated, it was inserted into the equation to find molecular weight and divided by the calculated moles solute. To find the percent error of the experiment, use the equation: Theoretical MW-Actual MW ÷Theoretical MW ×100. Phase changes occurred in this experiment when each solution was placed into each different temperature bath. The phase change that occurred was from liquid to solid when the t-Butyl solution was placed into the pure bath. Dynamic equilibrium occurs in the solution as the concentration of the t-Butyl and unknown solution increases and the rate of crystallization of the t-Butyl solution also increases. Super cooling occurred as the concentration of the solutions
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This note was uploaded on 11/03/2011 for the course CHM 1046L taught by Professor Simmons during the Spring '11 term at Tallahassee Community College.

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Determination of the Molecular Weight of an Unknown Non -...

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