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CHem 232 Final Vocab Lab 1-5
Terms in this set (37)
What are the 4 techniques used in lab?
2. Simple Distillation
4. drying Organic Liquids
Process in which liquid is converted into vapor by heating (boiling) and then condensing the vapor back into liquid in a seperate vessel.
The ___ is the sum of the vapor pressure of a liquid and that of air.
When a ____ is reached at which equilibrium vapor pressure of the sample equals the total pressure, rate of evaporation increases dramatically, bubbles form and the sample boils.
Allows separation of components if their boiling points differ by 40°-50°
When a liquid is composed of two volatile components, #molecules in X,Y in a volume of vapor is proportional to their respective partial vapor pressures
___ ratio measures he amount of condensate returning to the pot and the amount of vapor being collected.
If temperature rises, molecular motion, # molecules escaping and equilibrium vapor pressure all increase
The Partial Pressure of A is equal to the vapor pressure of pure A multiplied by the mole fraction of a.
The Mole fraction of A in the vapor is equal to the partial pressure of A divided by total vapor pressure
For a mixture to be 'Ideal
at any given temperature, the most volatile component has a greater fraction in the vapor than in the solution
Suggest 2 distillation methods by which are seperated of at least 5 theoretical plates could be achieved
Fractional distillation and Simple Distillation 5x
explain how using 60 ml of water rather than 30 ml would affect the amount of material recovered . Why?
a greater amount of water might decrease the amount of material because it will not only take longer to boil but also longer to recrystallize, also greater impurities arise a
Explain how an impurity would affect the melting point of your product
because an impurity disrupts the intermolecular forces and bonds in the crystalline lattice of the product it lowers the range at which the kinetic energy is greater than the forces that hold the product together, therefore it lowers the melting point
Explain why water is either a good or poor solvent choice for a recrystallization of benzoic acid that contains a sodium chloride impurity
it can be both extremes so wither impurity can have low solubility at all temperatures and thus soon with composition can be decanted or it can have high solubility so that composition can be poured. g
Benzoic acid is highly soluble in water while silicon dioxide is insoluble. Explain how you separate a mixture of the two compounds
1. Boil the mixture in water and on a hot plate until the soluble benzoic acid is dissolved but the silicon dioxide remains as an insoluble
2. Decant the dissolved ion into another flask with enough water in it, leaving impurity behind
3. allows solution to cool to room tempo, then insert it into a water bath to crystalize
4. use vacuum filtration to separate any impurity that may have but been with the decantation. After the crystals are dried they should be pure and without any silicon dioxide
Steps to Recrystallization?
1. Adding an appropriate solvent to the impure material
2. Heating the suspension until everything dissolves
3. Cooling the solution to allow the product to crystallize
4. Isolating the purified solid by vacuum filtration
5. Drying the purified solid.
Explain why the solvent is heated and cooled in ice bath
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.
Why do we use a minimum amount of solvent to dissolve the solid that is to be recrystallized?
It cleans off any residual soluble impurities clinging to the surface of the desired crystals
State the factors that limit the amount of solid that forms in the recrystallization process?
-solubility, temperature cooling and temperature heating
Why is a vacuum required for the rotoevaporation
to reduce pressure
State the purpose of the vacuum filtration
is a technique for separating a solid product from a solvent or liquid reaction mixture
Why do we wash the solvent from vacuum filtration
because too much material can stick to the dry agent and reduce the yield.
How can you lose product with vacuum filtration
Washing with too much solvent
State the purpose of drying agent
When we need to remove water, we use chemicals to remove excess water
Purpose of acid/base extraction
a powerful method for purifying mixtures in the work up procedure of a reaction
State the purpose that the addition of an acid or base serves to promote the extraction process
It helps us bring out the wanted product or convert the original solvent into what we want or need.
The strongest acids have _________ Ka values and ________ pKa values.
The strongest acids have large Ka values and small pKa values [pKa = -log(Ka)].
As acid strength increases, pKa __________.
The strongest bases have ________ Kb values and __________ pKb values [pKb = -log(Kb)].
large Kb values and small pKb values.
As base strength increases, pKb ____________.
The conjugate base of a strong acid has a very ________ Kb value.
small Kb value.
In general, as acid strength (and Ka) increases, the strength of the acid's conjugate base _________.
The conjugate acid of a strong base has a very _______ Ka value.
small Ka Value
In general, as base strength (and Kb) increases, the strength of the base's conjugate acid _______.
How are the organic layer and aqueous layer identified in the separatory funnel
It goes by density, the heavier compound will be on the bottom, however the less dense will be on top.
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