i need help with me chemistry homework

Melting Point

1.  Solids are often classified as being crystalline or amorphous in nature.  What does it mean for a solid to be crystalline and what happens when molecules have enough energy to melt?

2.  If solid A melts at 50 oC and solid B melts at 70 oC, what does this imply about difference in the strength and number of intermolecular interactions between the two different solids.  What are the three primary kinds of intermolecular interactions?

3.  When a solid product is slightly contaminated, how is the melting point different?

4.  Would you be able to speculate on the level of purity of a new, never before been made compound by melting point alone?  Explain.

5.  If you have 2 different solids mixed at exactly their eutectic point ratio, would the mp have a significant range?  Briefly Explain.

6.  If an unknown has an observed melting point of 90 – 93 oC.  Is the unknown more likely compound A with a reported melting point of 95.5 – 96.0 oC or compound B with a reported melting point of 90.5 – 91 oC?  Explain? (does slight contamination raise or lower a mp?)

7.  If 3 test tubes, labeled A, B, and C contain substances with approximately the same mp, how could you prove the test tubes contain three different chemical compounds by melting point alone? (hint: if you were to mix A and B and they were the same compound, how would the mp of that the mixture be different from a mixture of A and B if they were different?)

8.  What is sublimation and how does it affect melting point determination?

Boiling Point

9.  Using a melting point apparatus for boiling point determination, do you record the temperature when the stream of bubbles from the microcapillary begins or ends?

Thin Layer Chromatography

10.  TLC plates are composed of silica gel that is adhered to aluminum.  Is the silica gel the stationary phase or the mobile phase?  Why does it make sense that it is given this name?

11.  What kind of substances bind most tightly to the silica, polar or non-polar?  Does this mean they move up the plate fast or slow?  Briefly explain.

12.  In what order (from top to bottom) would you expect to find naphthalene, butyric acid and phenyl acetate on a silica gel TLC plate developed in a dichloromethane mobile phase?  Why do you expect this order?  (Hint: evaluate the polarity of the compounds especially see what your Wade textbook has to say about the polarity of carboxylic acids.  Dichloromethane as the solvent plays no role in the order of the compounds on the TLC plate.)

13.  What problem will ensue if the level of the developing solvent is higher than the applied spot in a TLC analysis?  What problem will ensue if a TLC plate is left in the developing solvent too long beyond the time point when the solvent reached the top of the plate?

14.  Would you be able to speculate on the level of purity of a new, never before been made compound by TLC along?  Explain?

15.  Why might it be very difficult identify cis 2-butene from trans 2-butene by thin layer chromatography? (hint:  what physical property does TLC evaluate?)

16.  What property is missing if an organic compound does not show a spot on a TLC plate when being analyzed by a UV light?  In evaluated the structures in activity #5, what bonding characteristic do you think imparts UV light absorption?

17.  If a known compound has an Rf value of 0.62 but you find your compound to have an Rf value of 0.55, what might this mean?  Explain in good detail.

18.  There are other techniques that can be used to identify a compound but these techniques require instruments that are usually not readily available in a teaching laboratory.  Using the internet, research the following two identification techniques and describe them in a single sentence.

A.  What is elemental analysis and what details does it provide about a molecule.

B.  What is mass spectrometry and what details does it provide about a molecule.