1. In re-crystallization method, if a compound was crystallized during the hot filtration step, what is the best way to overcome this problem? 2. In coupling reaction for the preparation of Methyl orange indicator, NaCl was added in re-crystallization step, give reason and discuss.

3. How poly phenols (tannins) can be removed from a solution containing Caffiene?

4. Which method is more efficient for the extraction of natural products? Reflux or Soxhlet? Why?

5. How a mixture of salicylic acid and 3-methylxanthine can be separated?

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.

a. energy is absorbed in the reaction.

if in a given reaction the energy of products is greater than the energy of reactants it means that reaction is endothermic and during the reaction, the energy is absorbed by reactants. in an endothermic reaction, the products have more stored chemical energy than the reactants. and in this reaction the reactants are more stable than products before the compounds with less energy are always more stable.