In: Chemistry
pre lab question:
Formulate a hypothesis that address the following question: How will adding more alcohol to a solution of potassium oxalate and iron oxalate affect the size of the crystals that form from this solution?
The crystals formed from the solution are of potassium ferrioxolate. When the concentration of alcohol increases in the system, it increases the Gibbs Free Energy of the system. Since is directly proportional to the rate of a reaction, (from the below equation)
If K is the rate constant for the formation of crystals, it increases with high concentration of alcohol.
Addition of alcohol simply to precipitate the crystals gives small crystals since high of the system causes high K value and hence the crystals are formed very fast. Formation of crystal in a less time allows it to form many small crystals instead of further growing in size. But, addition of alcohol on the surface of the solution slowly allows it to diffuse slowly through the solution and causes it to grow slowly over a period of time causing larger sixe crystals unlike the formation of many small sized crystals in the earlier case.