10) If you took a melting point of a compound before and after crystallization,
ID: 579066 • Letter: 1
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10) If you took a melting point of a compound before and after crystallization, what would you expect to observe? 11) A long time ago, in the 19th and the first half of the 20th century, the ultimate proof for identity of a crystalline organic compound was the so-called "mixed melting point". Here is how it worked: If you thought you had prepared or isolated compound Y, say of melting point 110 °C, then you would try to get a sample of the compound known to be Y (this was before you could order chemicals online). You would mix a little bit of the "authentic Y" with the sample you thought was Y and record a melting point of the mixture. How could this procedure be used to determine identity?Explanation / Answer
10) If you take before and after recrystallising (often done to purify the sample)..Before purification the melting point will be below the textbook melting point. Typically, impurities lower the melting point. The melting point may be 'fuzzy' with the sample melting over a range of temperatures. After recrystallisation, the melting point will be higher and should be 'sharp' (all the sample melts at one temperature).
Recrystallization (or Crystallization) is a technique used to purify solids. This procedure relies on the fact that solubility increases as temperature increases (you can dissolve more sugar in hot water than in cold water). As a hot, saturated solution cools, it becomes supersaturated and the solute precipitates (crystallizes) out. In a recrystallization procedure, an impure (crude) solid is dissolved in a hot solvent. As this solution is cooled, the pure product crystallizes out and the impurities stay dissolved.
you take a melting point before and after a purification technique (like recrystallization).
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