1. What four wrong procedures will cause a false melting point? 2. What are acti
ID: 1028053 • Letter: 1
Question
1. What four wrong procedures will cause a false melting point?
2. What are activated carbons used for, and what happens if to much is used?
3. GC: which type of compounds will have long retention time depending on molar mass and polarity?
4. What would be expected of RF values when adding extra polar and nonplar solvents?
5. What reactions cause gas for solvent extraction?
6. When would you use simple distillation and when would you use fractional distillation?
7. What is eutectic point, and how to find distillate?
8. How can we determine good solvent for recrystallization (should be 4 factors)?
9. What do the beads in the fractional column do?
Explanation / Answer
1) a) If your sample contains an impurity, its melting point range will be lower and/or wider than that the literature value. Similarly, extra impurities in the sample will increase this effect. b) If you are heating your sample too fast than a melting point will vary from the literature values. c) if a melting point capillary contains too much or too little sample then it will cause errors in melting point, d) If the sample is not packed firmly packed in the bottom of the tube then heat will not transfer uniformly which will cause an error in melting point.
2) Generally activated carbons are used in our daily life such as air purification, gold purification, metal extraction, water purification, medicine, sewage treatment. These activated carbons are also used as air filters in gas masks and respirators, in compressed air. Every application has an amount of activated carbon present in it. If too much-activated carbon will be used, nothing will happen as such. But some of the major disadvantages of activated carbons are there you need to know such as when it is used as air filters then the filter does not filter out nearly enough contaminants because of its pore size. Therefore, it is not much explored.
3) We need to understand that retention time is the time for a compound to spend in the column after it has been injected. Now, if your sample contains a number of compounds, then each compound in your sample will have a different retention time. The unit of retention times is seconds or minutes. Molar mass does not have any effects in the GC but if you will inject too much of the sample, then the peaks show a significant tailing, which causes a poorer separation. Furthermore, If the polarity of the stationary phase and compound are similar, the retention time will increase because the compound interacts stronger with the stationary phase. As a result, polar compounds have long retention times on polar stationary phases and shorter retention times on non-polar columns.
4) We need to remember that retention factor (Rf) values depend on:
• The polar nature of the solvent used ()
• Polar nature of the stationary phase
• Polar nature of the sample.
If your sample is polar in TLC than you can use polar solvents but whereas when your sample is non-polar then you have to use non-polar solvents because if you will use a polar solvent for non-polar compounds it will come immediately n the column chromatography.
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.