orgo lecture 2 - Additional points to consider Eutectic...

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Additional points to consider: Eutectic point vs. melting point of pure compound: Similarity: narrow melting range (E) Difference: lower than pure melting point (E) Game: real melting range is 65-95 Real range = eutectic point tp upper range Observed range, look between ballooning curves Graph of obs and range, be able to interpret What to consider when determining identity of unknown: What is the first set of If you were given a choice, would you pick standards with if it if it melts at 126 to 128 you look at things that melt in that range ie 126- 130 (narrow it down to around that range would you pick something with higher or lower mp? Impurities lower mp so if unknown are impure so it could probably be something with a higher melting range o You can eliminate things that are lower Why? What does an impurity do to a melting point?  lower it Postlab: 1) remark on the purity of the sample based on melting range and accuracy Did mp match literalure? o No w wide range so impure with source of error 2) statement on melting point and range for mixtures Mixtures by def are impure = lower mp with wider ranges
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3) Melting point composition graph (draw and find eutetic point, eutectic temperature and composition) Eutectic Point Graph Draw graph using data from melting points of pure urea, pure cinnamic acid and the mixtures of the 2 components (#2 and #3). From graph, estimate eutectic temperature, and composition of urea and cinnamic acid at the eutectic point (remember, it will not be 50:50). o Melting Point Composition Graph to draw your eutectic point diagram, you should plot your lower range and upper range of each melting point you take on your graph. o Then, draw a BEST FIT STRAIGHT LINE connecting either 2 or 3 of the upper ranges from the right side of the graph and a BEST FIT STRAIGHT LINE connecting the remaining 2 or 3 of the upper ranges from the left side of the graph. The criteria: Make sure the two straight lines intersect at a point that is lower than any of your lower ranges. You can only go through 1 data point on right and one on the left. You will need to draw several versions of this graph, adjusting the lines until the lines fit the criteria - so practice on other graph paper before transferring this graph to your lab notebook. Example of eutectic diagram shown under "Resources" for first experiment posting. need to change something… uhh data points should be wider X=% Y= Temperature Mp X= urea or CA MPY=urea or CA Intersection= eutettic point draw line across and label eutectic temperature extrapolate point to x axis label and know that number list composition 4) Identifying unknown and reasoning it was confirmed by taking the melting point of unkown + standard and temp did not go down
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5) Sources of Errors (you will need this section for every experiment) just list in lab report •Why some melting points may not have agreed with literature melting points
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  • Spring '09
  • Govindarajoo
  • Solubility, Solvent, Crystal, eutectic point

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