Post and pre lab questions for chem 231 | experiment 1

Your goal is to separate two solids by adding water and then filtering the mixture. What are the final steps of ending up with two separate solids?

Scrape the solid off the filter paper into one container and evaporate the water from the filtrate to isolate the other solid.

What is the best course of action if solid material remains in the flask after the heating step of a recrystallization?

Select one: ---> Allow the mixture to cool, then filter the mixture. ---> Redo the heating step of the recrystallization. ---> Remove the solid with a spatula. ---> Filter the hot mixture

After a recrystallization, a pure substance will ideally appear as a network of ___________. If this is not the case, it may be worthwhile to reheat the flask and allow the contents to cool more __________

large crystals, slowly

Identify the characteristics of a good recrystallization solvent.

--->Dissolves a chemical sample well at high temperatures. ---> Dissolves a chemical sample well at low temperatures. ---> Is not an organic liquid with a low boiling point. ---> Does not dissolve a chemical sample well at low temperatures. ---> Does not dissolve a chemical sample well at high temperatures.

expected mp for the recovered acetanilide.

115 C

solid, liquid, on a watch glass, evaporate

After a mixture has been poured through filter paper, the ____________ component remains on top while the _________ flows through. To collect the solid, spread the filter paper ________ and allow the solvent to _________

decanting, stirring, solvent

After assembling a gravity filtration apparatus, begin the separation of a mixture by _________it into the filter paper. Pour the entire contents of the mixture into the filter paper, ____________ the solid in the filter paper if needed to speed up the filtration. After all the liquid has drained through the filter paper, finish by rinsing the solid with _____

If you had chosen petroleum ether instead of your solvent what would happen?

If I chose petroleum ether as my solvent instead of water, my recrystallization experiment will not work since acetanilide is not soluble at all in petroleum ether. Recrystallization procedure works only based on the solubility properties of the compound of interest. If the compound of interest is not soluble in a solvent, that solvent cannot be used in the re-crystallization experiment. In order for my recrystallization experiment to work, I need an effective solvent for acetanilide. This solvent should only dissolve acetanilide at a higher temperature, not at room temperature. My solvent for acetanilide should be also soluble for the impurities species at all temperature to ensure this recrystallization experiment works. Since petroleum ether doesn't meet the requirement for effective solvent in for my experiment, the experiment will not work with petroleum ether as solvent.

Is your percent recovery of crystals within reason of what you would expect? Explain your answer

My percent recovery of crystal was 71 percent. This percentage is certainly within the reason of my expectation since most recrystallization procedure are not very efficient or nearly perfect. Furthermore, there are possible sources of human errors in this experiment when working on it in the lab. For instance, if I didn't heat my sample slowly as expected or didn't let my sample cool down slowly as possible to form crystals. Also, some impurities in my solution might have solubility properties that doesn't differ extensively from my compound of interest, which make it hard to purify compound of interest. Our lab manual also indicated that percent of recovery between 50% to 70% are common. For these reasons, I believe my percent recovery is within my expected value.

adding a small amount of water, slowly decant, into the middle of the filter paper

Once the vacuum filtration set-up is complete, start by _____________ in the filter funnel. Then, _______ the mixture________

describe what you should see during recrystallization?

Recrystallization is a useful procedure that can be used to purify a specific compound of interest based the compound's solubility properties. Generally, in recrystallization, we should see crystals of our compound of interest forms after dissolving our compound in a hot Solvent (specific solvent that only dissolves our compound at higher temperatures, not at a room temperatures) and then waiting for it to cool. We only see the crystal of our compounds of interest forms while the remaining impurities remain dissolved.

What would it mean if the melting point had a wide range in temperature rather than a narrow range of one to two degrees?

The melting point can be very useful in identifying a certain compound. A wide range of melting point temperature that is more than 2 degrees indicate low purity of the given compound, which is reasonable. When a compound of interest in a liquid form contains impurities, these impurities will disrupt the crystal lattice formation by preventing the atoms of our compound from coming close together to one another for packing to form a solid compound. As a result, the compound will have lower melting point than its pure form. A small melting point range indicates that compound of interest has a high purity since there is no impurities.

Would there have been a change in your results if activated carbon was not added to the solution before recrystallization?

There would be a change in my results if I didn't add the activated carbon since it's plays a role in the purification process of a compound of interest. The activated carbon is used to absorb impurities that cause the incorrect color in the solution before recrystallization. Without the addition of the activated carbon, crystals of our compound of interest might contain color impurities that gives a different color than the correct color (pure color) of the solid compound of interest. Although the activated carbon remove color impurities, recrystallization procedure will still work without the addition of the activated carbon as long the procedure is done correctly.

Why might activated carbon be added to a sample during the recrystallization process?

To absorb impurities causing the recrystallization solution to have an incorrect color