question

What is the purpose of recrystallization

answer

primary method for purifying solid organic compounds

question

Explain why the solvent is heated and cooled in ice bath

answer

The desired compound along with the soluble impurities are dissolved in a minimum of near boiling solvent, the solution is then allowed to cool slowly without interruption. As it cools, the solubility of the compound decreases and the solution becomes saturated with the desired compound and the compound begins to crystallize.

question

Why do we use a minimum amount of solvent to dissolve the solid that is to be recrystallized?

answer

It cleans off any residual soluble impurities clinging to the surface of the desired crystals

question

State the factors that limit the amount of solid that forms in the recrystallization process?

answer

-solubility -temperature cooling -temperature heating

question

The purpose of Rotoevaportation

answer

a device used for efficient and gentle removal of solvents in large amounts

question

Why is rotation required in Rotoevaporation

answer

to reduce the possibility of bumping and greatly increase the surface area of the solution

question

Why is a vacuum required for the rotoevaporation

answer

to reduce pressure

question

When is rotoevaporation utilized

answer

to evaporate dilute solutions obtained from extraction procedures or from chromatographic separations

question

State the requirement of the solvent for effective use of the rotovap

answer

The boiling point has to be high

question

State the purpose of the vacuum filtration

answer

is a technique for separating a solid product from a solvent or liquid reaction mixture

question

Why do we wash the solvent from vacuum filtration

answer

because too much material can stick to the dry agent and reduce the yield.

question

How can you lose product with vacuum filtration

answer

Washing with too much solvent

question

State the purpose of drying agent

answer

When we need to remove water, we use chemicals to remove excess water

question

How can using too little or too much drying agent

answer

You can lose your product, use too much agent can cause a loss of product by absorption from the drying agent. -use too little and water will remain and the product will be wet

question

What affect does impurities have on the melting point

answer

impurities lower the melting point

question

Whats the purpose of melting point

answer

tells us how pure the compound is

question

What effect does the sample size of the melting point have on the melting point

answer

Too little can cause a mp range of too little.

question

What effect does the rate of heating have on the melting point of a solid

answer

broad melting range, melting range will be high

question

Purpose of acid/base extraction

answer

a powerful method for purifying mixtures in the work up procedure of a reaction

question

State the purpose that the addition of an acid or base serves to promote the extraction process

answer

It helps us bring out the wanted product or convert the original solvent into what we want or need.

question

Ka and Kb

answer

The strongest acids have large Ka values and small pKa values [pKa = -log(Ka)]. As acid strength increases, pKa decreases. The strongest bases have large Kb values and small pKb values [pKb = -log(Kb)]. As base strength increases, pKb decreases. The conjugate base of a strong acid has a very small Kb value. In general, as acid strength (and Ka) increases, the strength of the acid's conjugate base decreases. The conjugate acid of a strong base has a very small Ka value. In general, as base strength (and Kb) increases, the strength of the base's conjugate acid decreases.

question

How are the organic layer and aqueous layer identified in the separatory funnel

answer

It goes by density, the heavier compound will be on the bottom, however the less dense will be on top.

question

State factors that affect the amount of compound extracted from the organic layer into the aqueous layer

answer

Certain compounds such as salt can disrupt the aqueous layer, by making it more polar. This will decrease the solubility of the compound in the aqueous layer.

question

The purpose of spectroscopy

answer

used to confirm identity of a compound

question

What information can we get from the spectroscopy?

answer

We can identify unknown compounds and the functional groups

question

Why are salt plates used in IR rather than glass

answer

-glass can absorb the compound, whereas salt is less likely too. They are also more transparent.

question

The purpose of distillation

answer

-to purify a compound that is pretty much pure, completely

question

The advantage of using distillation to carry out a chemical reaction over simply heating a reaction mixture.

answer

Compounds would decompose at high temperatures necessary to vaporize. However, because the boiling point is dependent on pressure, the distillation at reduced pressure, under a vacuum can make this possible.

question

Purpose of reflux

answer

process of boiling reactants while continually cooling the vapor returning back to the flask, as a liquid Used to heat a mixture for long period of time at certain temperatures

question

Advantage of using reflux rather than simply heating a reaction mixture

answer

-it can be left for long periods of time without need to add more solvent or fear of the reaction vessel boiling dry, as any vapors is returned from the condenser

question

Thin layer chromatography purpose

answer

is the separation of a mixture of two or more different compounds or ions by distribution between two phases, stationary and mobile

question

Stationary phase

answer

-a solid or a liquid supported on a solid -is the silica gel on the plate

question

Mobile phase

answer

a liquid or a gas -is the solvent or mixture of solvents

question

Process of stationary and mobile phase

answer

-as a solution is placed on the column, each molecule in the solution has to decide if it will stay in the solution (mobile phase) or adhere to the solid (stationary). The two compounds dissolved in the original solution will have different partitionary factors, meaning that one of them will adhere more to the stationary phase than the other. This partitioning can be governed by a multitude of factors, polarity, solubility, hydrogen boding, volatility. A more polar molecule will adhere more strongly to the more polar stationary phase than a less polar molecule.

question

Rf values of TLC

answer

-value for each dye is then worked out by distance traveled by component/distance traveled by solvent -the less polar compound moves higher up the plate resulting in a higher Rf value -a more polar won't move far

question

Salt plates

answer

-polished sodium chloride -transparent to infrared radiation -salt dissolves on plates when placed on the plates -moisture in the air causes salt plates to become cloudy, this is why we store them. -if damaged it will through off the IR spectrum

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