Place about 300 ml of water in a 500ml beaker and heat to about 90 deg C. You wi
ID: 715767 • Letter: P
Question
Place about 300 ml of water in a 500ml beaker and heat to about 90 deg C. You will use this water bath to heat your solution. Clamp your tube and contents on a ring stand. Place a notched stopper through Which is suspended a thermometer probe and a wire stirrer, into the mouth of the test tube. Lower the tube into the hot water bath and stir the contents with the wire stirrer until the crystals have all dissolved. Remove the tube from the water bath and allow the contents to cool while continuing to stir the mixture. Carefully observe the contents of the tube while cooling is occurring and note and record the temperature at which crystals first appear You need to be careful of refluxing. This occurs as hot water vapor contacts the cool test tube side and condenses, running down the side of the test tube. As this cool water reenters the solution, it can cause premature crystallization due to its lower temperature.
Temperature ()
Solubility (gKClO3/100gH2O)
80.0
38.89
64.9
27.05
52.9
20.83
47.5
16.94
44.0
14.27
Answer question: what refluxing is and how it could have caused you to have overestimated the temperature at which you considered crystals to first appear. I record the first crystals appear at 80-degree Celcius.
Temperature ()
Solubility (gKClO3/100gH2O)
80.0
38.89
64.9
27.05
52.9
20.83
47.5
16.94
44.0
14.27
Explanation / Answer
Refluxing is a technique that comes handy when there is a need to heat solutions for a long time {for the reaction to complete} without losing the volatile solvent. The solvent is heated continuously and let to vapourise , where the vapours are let to pass through a condenser which is relatively at a cool temperature than the heating vessel. As the vapours reach the walls of the condenser, they condense and return back to the boiling vessel.
It can be distinguished from distillation by the fact that vapours that rise are collected separately in distillation, while the vapours are cooled at the walls of the container and return as condensate to the original solution in reflux. Reflux is usually carried out at the solvent's boiling point.
Crystals form out of a supersaturated solution when the solution is subject to gradual cooling, and this phenomenon underlies the principle of differrnce in solubility of a salt with changing temperature.
Crystallisation is uniform and free from flaws when the entire solution is cooled homogenously. The problem with refluxing is that the relatively cooled condensate retuning back to the solution causes temperature decrease in a small region surrounding it, where crystals form out of the solution. However, the other major part of the solution will still remain enough hot to not allow crystal formation.Thus, we end up in overestimating the temperature of crystal formation.