Fall Flashcards
The general technique of crystallization involves dissolving the material to be crystallized in hot solvent and cooling the solution slowly. Otherwise stated a solvent that dissolved little of the material to be crystallized when cold but a great deal of the material when hot is a good solvent for crystallization.
True.
A good crystallization solvent is one which the material to be purified is insoluble at room temperature (cold) but is soluble hot. Then as the solution is cooled to room temperature then put on ice with the hope that pure material crystallized and the impurities stay in solution.
An organic chemist uses the melting point for?
Identifying a compound and establishing its purity.
Melting point indicates purity in two ways, the purer the material the lower it’s melting point and the purer the material the broader it’s melting point range.
False
The purer the material the higher the melting point and the narrower the melting point range.
Adding successive amounts of impurities to a pure substance generally causes it’s melting point to decrease in proportion to the amount of impurity added (and will cause the MP range to broaden).
For a reaction: A + B (statin material)—> C (product)
Calculate the theoretical yield when the limiting reactant is B which 1.2 moles and the molecular weight of C = 180.6 g.
Theoretical yield= moles of limiting reactant (x stoichiometric ratio) x MW of compound.
Ex: 1.2 moles (x1 mole of B : 1 mole of C) x 180.6= 216.72
What is the percent yield from question 4? When the actual yield of C is 120.4 g.
Percent yield= (actual yield/ theoretical yield) x 100
Ex: (120.4/216.72)x 100= 55.6 %
Scratching the flask with a spatula during re-crystallization….
Induces crystallization
Which answer gives the best definition of an organic extraction?
The transfer of a solute from one solvent to another is called an extraction.
Transferred to the second product because it is more soluble in the second solvent.
Two layers must not be miscible (desperation of layers must be observed).
A 2.3 g mixture A was made up of compound B and C. After performing an acid-base extraction it was found that 1.0 g of B and 1.1 g of C was recovered. What was the weight percent recovery?
Weight percent recovery = weight of the substance isolated/ weight of original material x 100.
Ex: B —> weight % recovery= (1.0 g/2.3 g) x 100= 43.5%
C —> weight % recovery= (1.1 g/ 2.3g) x 100= 47.8%
When using a separatory funnel which criteria are used to determine which layer is the aqueous and organic?
Know the densities of the two layers (lighter density on top).
AND add water to the funnel and see what layer it goes to ( will go to the aqueous layer and increase volume of the aqueous layer)
Treatment of a mixture p-nitroaniline and benzoic acid with 6M HCl produces?
A salt that is soluble in the aqueous layer. Formation of the aqueous layers and organic layers.
Addition of anhydrous sodium sulfate (Na2SO4) to the ____________ layer is dine until the granular (Na2SO4) does not ____________ together.
Organic; clump
Distillation is useful for separating s liquid mixture when the compounds have_______
Different boiling points or when one of the components won’t distill.
Fractional distillation is used when?
The boiling points of the components to be separated are close together.
The temperature observed during distillation of a pure substance remains constant throughout the distillation so long as both vapor and liquid present in the system?
True—> the mixture of compounds vaporized and the condenses at first (in the beginning of the column) the mixture is still a mixture but as it moves up the column the mixture separates.
Your distillation graph will plot on the X axis__________ and on the Y-axis ____________.
X-axis: volume of distillate (mL)
Y-axis: Temperature (C)
Which graph from question four will give you the most accurate data to identify the boiling point of your unknown?
Fractional distillation graph
TLC technique which statement is the best answer?
TLC is based on the functional groups of the compounds (its polarity) as the solvent front moves up the plate the components of the mixtures will bind to the plate (solid phase) and the solvent (moving phase) will dissolve the compound off the plate together with the differences in the polarities the components will migrate up the plate at different rates.
“Like dissolves like”
Polar solute with a very polar solute will migrate too quickly.
Nonpolar with no polar will not migrate at all.
Polar solute with a polar/ non polar solvent migrated midway up the plate.
TLC technique
Important for rapid separation and qualitative analysis of small amounts of material.
The separation is based on many equilibrations the solutes experience between the moving and stationary phases.
Calculate the Rf value of the two spots of the TLC plate drawn in the board.
Rf value= distance travelled by solute/ distance travelled by solvent.
When choosing the appropriate solvent for TLC which criteria is the best answer?
Choosing a polar solvent and a polar solute (not too polar)
Or non-polar solvent with non polar solvent.
Ideal Rf value between .3-.7
Monitoring a reaction using TLC gives an organic chemist information about the progress of a reaction.
True—> can see if the reaction goes to completion.
If you slot the reaction mixture vs. The starting material; can potentially monitor the disappearance of starting material and know when the reaction is compete.
In part A of today’s experiment, the identify of the unknown is determined by which of the following criteria?
Comparing Rf values and knowing polarities.
If plane polarized light of passes through a solution containing two enantiomers the plane polarized light is rotated either to the right or to the left.
True—> plane polarized light rotated in equal but opposite directions for enantiomers
Refractive index is a physical property of liquids that measures purity and is temperature, wavelength dependent.
True
What does it mean for a compound to be chiral?
Has four R groups around the chiral carbon.
The optical rotations of the isomers (enantiomers) are of opposite sign the other physical properties should be….
Equal/ the same.
An instrument called the polarimeter is used to measure?
Specific rotation of the compound.
The synthesis of t-pentyl chloride proceeds by which reaction mechanism?
SN1
T-pentyl chloride is easily hydrolysis back to alcohol when in water and sodium bicarbonate solution.
True
The purity of the synthesized t-pentyl chloride can be evaluated by comparing IR spectrums. The t-pentyl chloride is a pure substance. It’s IR spectrum shows no evidence of an _________.
O -H peak
Which is the limiting reactant if you start with 2 mL of t-pentyl alcohol (MW= 88.15 g/mol; density= .805 g/mL) and 5 mL concentrated HCl (MW= 36.46 g/mol, density= 1.18 g/mL)?
T-pentyl alcohol
Ex: 5mL x 1.19g/mL= (5.95 g x 1 mole)/36.46 g= .163 moles of concentrated HCl
2 mL x .805 g/mL= (1.61 g x 1 Mole)/88.15 g= .018 moles of t-pentyl alcohol
The 5% sodium bicarbonate reacts with any aqueous solution acid (HCl) in the organic layer releasing carbon dioxide gas.
True— reason for venting
The synthesis of 4-methylcyclohexene proceeds by which reaction mechanism?
Elimination
The purpose of both bromine Br2 and potassium permanganate (KMnO4) tests to confirm the presence of a ___________
Double bond
Comparing the IR spectrum of 4-methylcyclohexene and 4-methylcyclohexanol what absorption is the major difference?
Loss of an O-H group and presence of a double bond functional group.
The purpose of treating the distillate (impure product) with saturated sodium chloride?
Remove any phosphoric acid that co-distilled with the product.
The alcohol dehydration that is being performed today is a base catalyzed reaction?
False, an acid catalyzed reaction.
