what is the advantage of carrying out distillation processes under reduced pressures??
And ALSO
can someone tell me the criteria used in selecting primary standards? i.e. NaHCO3, Na2CO3, KIO3, (COOH)2 and its salt as primary standard
yeh it is (provided that ur not being sarcastic here)
i'm wondering if by at reduced pressure, it would be somewhat easier to collect the distillates because the temp. is also reduced thus it would be easier to ascertain them as the temp aren't changing too rapidly...
The whole idea behind distillation at reduced pressure is that the boiling point is lowered, usually significantly. Therefore, something that boils at 250 C at 1 atmosphere (and is an organic material) PROBABLY will decompose (and there goes that compound it took you 2 weeks to prepare), BUT if the pressure is reduced it may boil at say 75 degrees C and it doesn't break apart at the lower temperature.
The second question, regarding primary standards:
For a primary standard, we want something that is relatively inexpensive, stable, has a known composition, reacts stoichiometrically with whatever we are trying to standardize, as well as reacting within a certain pH range (if acid/base) or redox potential (if a redox titration). I hope I have interpreted your question correctly.
The advantage of carrying out distillation processes under reduced pressures is that it lowers the boiling point of the liquid being distilled. This is beneficial because it allows for the separation of compounds with high boiling points or compounds that are thermally labile (easily decompose when heated). By reducing the pressure, the boiling point of the liquid decreases, enabling the distillation to occur at lower temperatures and minimizing the chances of thermal degradation or decomposition.
Now, moving on to the criteria used in selecting primary standards. Primary standards are highly pure substances that are used to accurately determine the concentration of a solution in titration or other analytical methods. The selection of primary standards is based on several key factors:
1. High Purity: Primary standards should have a known and high level of purity to eliminate potential sources of error in the analysis. It is crucial that impurities do not interfere with the analytical method being employed.
2. Stability: Primary standards should be stable under normal storage conditions. They should not deteriorate or decompose during storage, as this could lead to inaccurate results.
3. High Molecular Weight: Choosing primary standards with high molecular weights helps to minimize errors caused by weighing inaccuracies. High molecular weight compounds are less prone to measuring small inaccuracies in weight, resulting in more precise titration or concentration determinations.
4. Endpoint Detection: The primary standard should react stoichiometrically with the analyte being titrated. This ensures that the equivalence point (endpoint) can be accurately determined.
5. Availability: Primary standards should be readily available in sufficient quantities to allow for accurate and reproducible analysis. It is important that the substance can be easily obtained or prepared and has a reasonable cost.
In the case you mentioned, NaHCO3, Na2CO3, KIO3, (COOH)2, and its salt, these substances could potentially qualify as primary standards based on the aforementioned criteria. However, the suitability of each substance would depend on the specific requirements and characteristics of the analytical method being employed. Therefore, careful consideration and evaluation are necessary when selecting primary standards for a particular analysis.