a)There are two types of impurities that can contaminate a sample.What are they?

Question

a)There are two types of impurities that can contaminate a sample.What are they? How do they affect the observed melting points?

b)You have synthesized a new compound one which has never beenprepared. How would you determine its mp? What precautions couldyou take to insure that it is as accurate as possible?

c) You have a sample of an unknown substance, although you thinkyou know its identity. How could you establish whether or not thematerial is what you suspect?

d)Why shouldn't you use a sample that has been melted andresolidified to confirm a melting point?

e) A sample of an unknown compound has an melting point of145-154C. What conclusions would you draw? What actions would youtake?

Explanation / Answer

a) The two types of impurities that can contaminate a sample aresoluble and insoluble impurities. These impurities change

the melting point of the sample, so that now instead ofmelting at a specific temperature, it now melts over a rangeof

temperature.

b) The melting point can be determined by carefully heatingthe compound at a constant pressure (preferably at 1 atm),

so that it's melting point can be accurately known. Theprecautions taken are :

- It should be as free of impurities as possible

- The pressure should be constant

c) It can be determined by carrying out certain tests which weknow that the suspected compound would certainly give

positive results.

d) Because, due to the change in temperature, there can becertain change in the physical as well as chemical properties

of the compound.

e) Since the compound melts over a range of temperature, andnot at a fixed temperature, we can therefore concludethe

presence of impurities which do not allow it to melt at aconstant temperature.

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