What effect would each of the following have on the observed melting-point range

Question

What effect would each of the following have on the observed melting-point range of a sample? filling the melting-point capillary two-thirds full not packing the sample lightly in the capillary the presence of an insoluble impurity such as glass in the sample. Why should the heating rate during melting-point determinations be as slow as 1 or 2 degree C per minute Suppose your sample melts before you were ready to read the temperature. Should you cool the capillary and start again or prepare a fresh sample? Explain Suppose you have an unknown X that melts at 85-86 degree C and you do a mixture melting point with a known compound A that melts at 85-86 degree C. What results would be observed if: X is identical with A X is not identical with A. Why is a melting-point range determined rather than the actual melting point of a compound? What does a broad melting-point range indicate about the purity of a sample? Gram for gram, table salt lowers the freezing point of water much more than table sugar. Explain. If a volatile compound sublimes and disappears before it melts, how can its melting point range be determined? If a compound is pure, how narrow should its melting point range be expected to be ?

Explanation / Answer

1. Effect on melting point of compound by

a. If the tube is filled with compound a lot, the compound would need more heat to reach melting point. Thus observed melting point would be higher than actual value.

b. If the samples are not packed tightly in the tube, the resultant melting point would be higher as heat would be needed to heat the air present as well.

c. If an insoluble impurity is present along with compound, the resultant melting point would depend upon the melting point of the unknown as well.

2. Slow heating ensures the compound reached the same temperature as the total amount of heat supplied at that time. Thus thermometer temperature would accurately represent the temperature of the compound in the tube.

3. If sample melted prior to temperature note down, one should prepare a fresh sample to remeasure the melting point.

4. If mixture of unknown X and known A both having same meltinf point are mixed together,

a. X is identical with A

Related Questions

Navigate

• Browse (All)
• Browse W
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.