Acinod's Question Thread

[acinod]

Why are H2SO4, HNO3, HCl and solid NaOH not suitable primary standards?

A sample of MgCl2 is placed in the flame of a Bunsen Burner. What component of the substance is responsible for the production of a flame colour?

Why can GLC also be used to for substances with much molecular weights above 300 such as steroids?

Would different infra-red and proton NMR spectra be obtained for pure organic liquids as opposed to samples dissolved in water? What differences would you observe and why?

Chlorine has two isotopes, CL-35 and Cl-37. Why will the mass spectrum of chlorine gas show 5 peaks?

If a mixture of 4 low molecular weight organic compounds are resolved using GLC, why would you not obtain 4 peaks?

Can a molecule produce multiple molecular (parent) ions?

Do weak acids require a greater volume of base as compared to the same volume and concentration of a strong acid to reach the equivalence point of a reaction? Explain your choice of answer.

[Vincezor]

Looks like similar if not same questions are here:

http://vce.atarnotes.com/forum/index.php/topic,41335.0.html

scocliffe09 has answered them as well

[acinod]

Got some questions on the 'Synthesis of Aspirin':

1. Explain what happens to the -OH group in the salicylic aid when acetic anhydride is added and what effect this has on the end product.
2. Why was the aspirin washed with cold water during the filtration process? How would this affect the end product and the actual product yield?
3. What happens if you forget to add concentrated sulfuric acid to the reaction mixture? What would you expect the ferric chloride test to show?
4. A total of 20 mL of ice water are used in processing the final reaction mixture (including the water used to rinse the precipitate). How many grams of aspirin could be lost in this process? (Assume the solubility of aspirin in ice water is the same as at 25 degrees.)
5. Identify one source within the experimental procedure that would result in a increase in yield.
6. Identify one source within the experimental procedure that would result in a decrease in yield.
7. What is the purpose of re-crystallization and how is this achieved?
8. Using the melting temperatures as your guide, explain your conclusion about the purity of the re-crystallized aspirin sample. (Melting temp. of aspirin before crystallisation=125C, after re-crystallisation=135C)