ASSIGNMENT INSTRUCTIONS for Expt 16 (Determination of Molar Mass by Freezing Point Depression)
Refer to postings in classes #27 and #28 (Tue 5/5 and Thu 5/7) for guidance. Review items in the module “Expt 16 (Molar Mass by Freezing Point Depression) Procedure Videos and Additional Info“. Instructions listed below take precedence over instructions for data treatment in the lab manual.
*Include ONLY the following five sections in your upload:*
(1) Title page:
Include your name, date, course info, experiment number, and title. Copy and paste the grading rubric for EEXPxpt 14 into the title page. Some credit for this assignment will come from the pre-lab. _Rubric-Expt16.doc
(2) Labeled plots:
The data you will use for this assignment is on the Student Data page in the module “Expt 16 (Molar Mass by Freezing Point Depression) Procedure Videos and Additional Info“. Insert the images of the plots of the temperature-vs-time data for ALL 6 trials into your document. Three plots are for the pure solvent (lauric acid), and three plots are for the solution of unknown in lauric acid. Organize this section with titling and labels so that it’s clear which plot is which. * On each plot, clearly indicate and mark the freezing point temperature. This temperature should correspond to a horizontally flat region in the graph (a region of no change in temperature over a period of time), which should have occurred while the liquid was freezing into solid. Alternatively, and if necessary, you may use the extrapolation process described on the page Info on Expt 16 (Molar Mass by FPD) in the module “Expt 16 (Molar Mass by Freezing Point Depression) Procedure Videos and Additional Info” on Canvas. * In addition to marking each plot, state the freezing temperature determined for that plot in degrees Celsius directly next to or under the plot.
(3) Table: freezing point of pure lauric acid:
Create a small table of the 3 determinations of freezing point of PURE lauric acid, and below the table report the mean and standard deviation.
(4) Table: data on solutions:
Create a larger table of data on the SOLUTIONS, including the following data and calculated values for EACH TRIAL: ~ trial number ~ mass of solvent ~ mass of unknown solute ~ freezing point of the solution ~ calculated molality of the solution ~ calculated molar mass of the unknown solute
Show your CALCULATIONS of *molality* and *molar mass* of the unknown substance for EACH solution you made. – Use the freezing point depression constant Kf = 3.90 Â°C/m for lauric acid as solvent. – Use the mean (average) freezing point of the pure solvent for the calculations. – From your 3 separate determinations of molar mass of the unknown substance, report a mean and standard deviation of the molar mass. – You do NOT have to calculate any percent errors (which was stated in the lab manual).
*There are no post-lab questions assigned for this lab.*
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