Chemistry Lab Procedures: Recrystallization, TLC, and Bromination Techniques

What is the initial temperature setting for the hotplate in the procedure?

250 ºC

What is the purpose of adding methanol to the neutral compound?

To dissolve the neutral compound by heating.

What should be done if the methanol begins to boil vigorously?

Turn the hotplate down or move the beaker to a cooler edge.

What is the next step after all solid dissolves in the neutral compound solution?

Remove the beaker from the hotplate and cover it with a watch glass.

What solvent is used for dissolving the base compound?

Boiling water.

What is the purpose of placing the beaker in an ice-water bath after cooling?

To promote the formation of precipitate from the neutral compound.

What is the purpose of vacuum filtering the neutral compound?

To isolate the solid product from the solution.

What is recrystallization?

A method of purification that relies on the different solubility of a pure compound and impurities.

What is the ideal characteristic of a solvent used in recrystallization?

It should dissolve the solute when hot but not when cold.

What is the significance of slow cooling in recrystallization?

It leads to better crystal purity.

What does microscopy help observe in the context of crystallization?

Crystal formation, morphology, and purity.

What is the stationary phase in Thin-Layer Chromatography (TLC)?

Silica gel or alumina plate.

What is the formula for calculating Rf in TLC?

Rf = (distance traveled by compound) ÷ (distance traveled by solvent front).

What is the effect of using a too polar solvent in TLC?

Spots run to the top.

What is the order of reactivity for bromination of C-H bonds in the experiment?

1. iso-Propylbenzene 2. Ethylbenzene 3. Toluene 4. tert-Butylbenzene.

What should be done if bromine is spilled during the experiment?

Pour sodium thiosulfate around the spill to neutralize it.

What is the role of cyclohexene in the bromination experiment?

To quench any residual bromine in the solution.

What should not be done with glassware that contained bromine?

Do not wash it with acetone.

What is the purpose of using polarized light microscopy?

To analyze anisotropic crystals and confirm their purity and identity.

What is the first step in the bromination procedure?

Obtain 8 disposable test tubes and label them.

What should be done after determining the order of reactivity in the bromination experiment?

Pour the contents of the tubes into an Erlenmeyer flask.

What is the purpose of using a Buchner funnel in the procedure?

To vacuum filter and collect the crystalline product.

What is the ideal Rf value range for effective solvent selection in TLC?

Rf ~0.3-0.7.

What is the significance of adjusting focus, light, and magnification in microscopy?

To properly examine solid products and crystal habit.