You wish to increase the heat pf the crystal solution in your test tube. How should you place it in the sand bath to achieve your purpose?
You should place the flask on the sand bath but first you should stablize it and then carefully place it. You can also place it deeper inside the sand bath and heat the solvent while test tube is still connected t the aspirator
Disposable glass pipettes
in red sharp container
If you are filetering suspended solids via pressure filtration with a micro Buchner funnel, what should you do to avoid crystallization in the apparatus? What should you do after this before going on to the crystallization step and why?
You should dilute the solution to be filtered so that it does not recrystallize and use a small amount of clean solvent to rinse the appartaus
2 errors that could keep a substance still impure after recrystallization
Solution was cooled too fast which would cause it to crash out as a powdered substance full of impuritites
If crystallizatzing solution is distrubed, too many nuclei for recyrstallization will form and lead to samll crystals that comeout of a solution alo
According to the exclusion concept of recrystallization, why do soluble impurities remain in solution (even when it is cold)
Too little impurities to saturate the solution
Which solvent are you heating up in the recrystalliztion of acetanilide from the solvent pair experiment?
Ethanol needs to be heated since acetanilide is more soluble in ethanol than water
What solvent would be the best to dissolve napthalene (water, ethanol, or tolune)
Toluene (both nonpolar)
A second crop of crystal can be btained to enhance the percent recovery. How does one start the process of obtaining these? What are the drawbacks?
The second crop of crystals can be obtained by recyrstallizing the the filtratrate. These crystals are not as pure
What major criteria would water have to satisfy in order to be used soley in recrystallization?
Water would have to be able to dissolve the substance in hot water but not cold water, dissolve all the impurities or none of them, and not be reactive with the solute
Procedure of how to use solvent pairs when no one solvent has ideal properties with respect to a solute
Add the better solvent (while its hot) until all solute is disslves
Add poor solvent unitl cloudy solution results
This makes sure the solution is saturated
Remedies for Unsaturated solution
Boil off excess solvent in aspirator tube until you hit point of saturation or lower the temp to lower the solubility of the solute in the solvent
Super saturated remedies
Use seed crystals to indice crystallization and scratch from the bottom of test tube with glass rod
Def of super heating and prevention
Heating above boiling point without boiling, To avoid use a boiling stick
(Never add boiling chips to an already hot solution)
Why crystals oil out? Remedies and prevention
Oiling out occurs when the temp of the solution is above the MP of the crystals, so the crystals will come out as small droplets (pretty impure) Remedy: lower the temperature at which the solution becomes saturated with the solute by simply adding more ro
Activated charcoal-purpose
the impurities can be absorbed onto the surface of activated charcooal by simky boiling the solution with charcoal. It has so much surface area it can bind to a large number of molecules.
Drawbacks of Charcoal
Charcoal is so finely divided it can only be seperated from the solution through the filter paper and the presence of charcoal completely obscures the color of the solution, so adding the correct amount of charcoal is a matter of luck. If too little is ad
Filtering of suspended solids-why not vaccum
vaccum can cool solution and cause recrystallization
Choosing solvent/pair (error)
Make sure impurities are dissolved completely or not at all, If partiall cannot fully seperate.
Dissolving (error)
Noiling stick not added = bumping. To much solvent will prevent saturation of solution. In a pair, if second solvent has lower bp than first, mixture will suddenly boil and spew hot liquid.
DEcolorizing
Don't add charcoal pieces to a superheated solution or the solution will boil over
Filtering
if you mistakenly use vacuum filtration, hot solvent can crystallize