HW 2. In order for melting point depression to be observed, the impurity must be

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 recrytallization (ndividual prmaetice ) 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

I will give you some points regarding recrystallization and factors that affect the melting point and percentage yeild of the crystals that will help you to understand the concept

1.Recrystallization is the method for purifying solid organic compounds.first of all solubility knowladge is important in order to determine which compound will dissolve in which solvent.a general principle is that  "like dissolves like".that is"compounds having similar structural features will be soluble in one another.

2.Recrystallization works when the proper solvent is used.generally a hot solution is used for the recrystallization process as compound dissolves more in hot solution rather than cold one

3.then it is allowed to cool slowly so that it can lead to good quality crystals.REMEMBER slow cooling is important in the process of forming good quality crystals.also dont disturb the solution during crystallization process

4.recrystallization is done in order to get more pure form of crystals by dissolving in appropriate solvent

5. different types of impurities that may be present in a sample: soluble, insoluble, and colored. the solution is filtered to remove the insoluble impurities, and the solvent is evaporated to produce the solid compound.

6.coloured solution is treated with charcoal to remove coloured substance.

7.IN OUR CASE IF WE WILL NOT ALLOW THE CRYSTALS TO SIT FOR EXTRA 5 MINUTES THE CRYSTALS WILL NOT BE COMPLETELY DRY SO THAT IT WILL AFFECT THE PERCENTAGE YEILD AS THERE WILL BE SOME LIQUID CONTENT ALREDY PRESENT WITH THE CRYSTALS.

8.HENCE IT WILL GIVE MORE WEIGHT ON MEASURING RATHER THAN THE ACTUAL WEIGHT OF THE CRYSTALS GIVING ERROR ON YEILD CALCULATION

9.ALSO THERE WILL BE SOME CONTAMINATION DUE TO WET FILTER PAPER .SOME SMALL PORTIONS OF THE FILTER PAPER MAY STICK WITH THE CRYSTALS GIVING MORE YEILD

10.IF WE TALK ABOUT MELTING POINT IN GENERAL IMPURITY DOES NOT AFFECTS (GENERALLY) THE MELTING POINT .

11.IF THE MELTING POINT OF THE IMPURITY ID MORE THAN THAT OF THE CRYSTALS THEN IMPURITY MAY DEPRESS THE MELTING POINT OF THE CRYSTALS.

12  THUS THERE MAY BE AN INCREASE OR DECREASE IN THE INITIAL MELTING POINT BUT FINAL MELTING POINT WILL BE SAME

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