HW 2. In order for melting point depression to be observed, the impurity must be
ID: 715895 • Letter: H
Question
HW 2. In order for melting point depression to be observed, the impurity must be soluble in the compound. Insoluble impurities such as sand or charcoal will NOT depress the melting point. However, impurities are not always other solids. An impurity that effects a melting point depression could also be a liquid! Look back at the steps for recrystallization (individual practice 1). Explain the purpose for performing step 10 and discuss what effect skipping this step would have on your recorded mp data and your % recovery data.Explanation / Answer
Whenever we synthesise any organic or inorganic compound, our aim should be to prepare that compound the purest form posiible with maximum yield.
Purity can be attained by recrystallising the compound.That crystals obtained after recrystalisation is the purest form of that compound.
Now as we have have recrystallised,we need to wash the crystals present on the Buchner funnel using a suitable solvent (solvent should not not dissolve the recrystalised product.).After the washing we need to keep for some extra time to ensure complete drying
Why we need to attain comlete dryness?
After recrystallisation our first joj is to take the weight of the recrystallised compound, which is then equated with the theoretical yied to get percent practical yied......Now if cold ice water is used to wash the crystals and if we dont dry the crystalls to completion,mass of water will also add up in while recording practical yield and we end up getting wrong percent practical yield.
Recrytallisation always decreases the yield of the crude compound.Therfore the recrystalised compound will have higher practical yield than the crude product if not dried well,which is theoretically wrong.
While taking Melting point (M.P) if molecules of solvent used for washing (eg water)may interupt and we will record a wrong physical contant.
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