Melting Points and Mixed Melting Points Experiment 1: Identify a compound by its melting point and mixed melting points. Acetamide p-Aminobenzoic acid Camphoric Acid trans-Cinnamic Acid Malonic Acid p-Nitrophenol Resorcinol Succinic Acid Urea 113 - 115 o C 188 - 189 o C 183 - 186 o C 133 - 134 o C 135 - 137 o C 113 - 115 o C 110 - 113 o C 187 - 189 o C 133 - 135 o C
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Experiment 1: Identify a compound by its melting point and ... a acetic acid - water solution with a mole fraction water of 0.9 Heat a acetic acid - water solution with a mole fraction
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Melting Points and Mixed Melting PointsExperiment 1: Identify a compound by its meltingpoint and mixed melting points.
Acetamide
p-Aminobenzoic acid
Camphoric Acid
trans-Cinnamic Acid
Malonic Acid
p-Nitrophenol
Resorcinol
Succinic Acid
Urea
113 - 115 oC
188 - 189 oC
183 - 186 oC
133 - 134 oC
135 - 137 oC
113 - 115 oC
110 - 113 oC
187 - 189 oC
133 - 135 oC
A sample is putin the bottom ofa melting pointtube.
Put a small amount of the compound in theopen end of the melting point tube.
Turn over and tape the closed end on the desktop until the compound falls to the bottom.
Sample in themelting pointtube.
Use a Thiele tube filled withmineral oil to heat your sample.
Attach the melting point tubeto a thermometer.
Heat about 5o per minuteuntil within about 10o ofthe melting point
Near the melting pointheat at 1 - 2o perminute
Mel-Temp in the lab
Temperature
Starts to melt Finished melting
m.p. = Start - Finish
Why is salt put on snow covered roads?
Ice melts at 0oC
What happens to themelting point if saltis added?
Ice melts!
Impurities such as salt lowers the meltingpoint of water.
Putting salt on icy roads causes the ice tomelt because it lowers the melting point ofwater.
Impure compounds usually melt lower thanpure compounds so the melting point maybe used as a measure of the purity of acompound
Acetic Acid, CH3COOH,is a colorless liquid thatmelts at 16.6oC.
Let’s look at the melting point ofmixtures of water and acetic acid.
Plot of melting point vs. mole fraction waterfor mixtures of water and acetic acid.
Eutectic point
Cool a acetic acid - water solutionwith a mole fraction water of 0.9
Heat a acetic acid - water solutionwith a mole fraction water of 0.9
Heat a acetic acid - water solutionwith a mole fraction water of 0.2
Pure compounds usually melt overa narrow temperature range, often1o or less.
Impure compounds melt lowerthan pure compounds and over awider temperature range.