Lab1_FreezingPtDepression2

Lab1_FreezingPtDepression2 - Determination of Molecular...

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Determination of Molecular Mass by Freezing Point Depression February 8, 2010 Abstract: The main goal of this experiment was to determine the molecular mass of isopropyl alcohol by measuring the freezing point of an aqueous solution of the alcohol. Freezing point change is directly proportional to the amount of solute dissolved in the water solvent. We had to measure consistent freezing points for water and isopropyl alcohol using an ice bath made of rock salt, ice, and water. We determined that the freezing point of the aqueous solution through a freeze/thaw procedure. Our freezing point for water was -2°C, which is lower than the known freezing point of water. Our freezing point for isopropyl alcohol was -7°C, which was lower than the rest of the class. Using the formula that represents the relationship between temperature, molality, and the molal freezing point depression constant (Δt f = k f * molality), we were able to determine the molecular mass of the alcohol to be 27.81 g, which is significantly lower than the known value of 60.1 g/ml. Results:
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Table 1: Raw Data Chemistry 211-212-202 Freezing Point Depression: Rachel L Palting V_water (mL) T_water (°C) V_alcohol (mL) T_alcohol (°C) 15 0.18 2 -4 15 0.375 2 -5 15 -1 2 -3 15 1 2 -1 15 0 2 -2.8 15 1 2 0.25 15 0 2 -2.75 15 0 2 -9 15 0 1.3 -2 15 0 2 -3 15 1 2 -2 15 -0.5 2 -4.5 15 2 2 -3.5 15 0.5 2 -4.5 15 -7.5 2 -8 15 1 2 -1.75 15 0 1.4 -1.5 15 -2 2 -7 15 0.5 1.4 -1.5 15 -0.5 2 -4.25 15 -2 2 -7 15 -1 2 -3 15 -0.375 2 -5 15 1 2 -1.75 Explanation: V_water (mL) = Volume of water T_water (°C) = Temperature of pure water V_alcohol (mL) = volume of Isopropyl alcohol T_alcohol (°C) = Temperature of Isopropyl alcohol and water Table 2: Calculated Data
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m_H2O (kg) m_Iso (g) dt_f (°C) m_expt (m) Mol (isopropyl) MW (isopropyl) % Error
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This note was uploaded on 02/28/2010 for the course CHEM 212 taught by Professor Staff during the Spring '08 term at George Mason.

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Lab1_FreezingPtDepression2 - Determination of Molecular...

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