If an insoluble impurity, such as sodium sulfate, was present in sample, would t
ID: 1089946 • Letter: I
Question
If an insoluble impurity, such as sodium sulfate, was present in sample, would the observed melting point of the sample be too low, too high, or would be no effect. Explain your reasoning.
Explain in detail why the melting point sample should be finely powdered and packed tightly into the cappliary tube.
Strickly speaking, why is it incorrect to speak of a melting point?
A student has an unknown with an observed melting point of 82..5 degrees Celisus -86 degrees Celisus. Is it Compound with a reported melting point of 83.5 degrees Celisus -84 degress Celisus, Comound Y with a repored melting point of 88.5 degree Celisus-89 degrees Celisus or Compound Z with a reported melting point of 82 degrees Celisus -83 degrees Celisus. Explain your reasoning.
An unknown compound is suspected to be acetanilide (mp 113.5 -114 degrees Celisus. What should happen to the melting point if the unknow were mixed with (a) an equal quantity of pure acetanilide? (b). an equality of benzoic acid?
Three test tubes, labeled A, B, C, contain substances with approximately the same melting points. Describe in detail how you could prove that the test tubes contain three different substances using only melting point tests.
Explanation / Answer
- If an insoluble impurity is present in a sample, it would reduce the extent of intermoelcular forces between the pure sample molecules as not impurities hold the place between the sample molecule and therefore the observed melting point would be too low. Less amount of heat is needed to break the remaining intermolecular forces left in the sample and do a phase change solid to liquid.
- If the capillary has spaces which has air in it, more heat would be needed not only to heat the sample but also to heat the air in the space and therefore, observed melting point would be higher than actual value.
- the unknown compound has a lower melting point and could be compound Z with an impurity.
- If the unknown suspected acetanilide is mixed with (a) known pure acetanilide sample, If the two compounds are the same, we would see the same melting point as that os acetanilide, otherwise their would be a change in the mixed melting point. (b) Similarly, mixing the sample with benzoic acid would lower the melting point as now the two are different compounds. Mixed melting points are a way to identify the purity and identity of a compound. If melting point changes for a mixture, the two compounds are different or else they are the same.