exam 1 Flashcards
difference between gravity and vacuum filtration
gravity is done when you want to keep the liquid and vacuum is done when you want to keep the solid.
vacuum is preferred because it takes the maximum amount of amount of solvent from surface of crystal
if you add more solvent what does it to the yield and purity of a crystal
you lose more yield but it will be more pure
best solvent pairs for recrystallization
one solvent is polar and the other is non polar, one solvent should be soluble at the boiling point of the compound while the other is insoluble at high temperatures.
3 isomers of c6H14 with all different melting points, whats true about them?
The polarity is approximately the same
the surface area decreases when it gets smaller
more symmetrical it is the more the London dispersion forces decrease
more surface area the higher the boiling point
when a solid is dissolved in a solvent which of the following procedures leads to crystals
cooling the liquid
partial evaporation of the solvent
addition of a seed crystal
addition of a solvent in which compound has low solubility
will there be better purity of the product of recrystallization if the solution containing solid is cooled slowly?
yes, less likely that impurities will be entrapped in the growing crystal
in recrystallization which of the following steps lead to a maximized yield of product?
minimal amount of solvent
if you heat isopropyl up in a water bath what will the temp be of the isopropyl acetate inside the flask and the gas phase above the liquid inside the flask?
temp of isopropyl acetate can only heat up to its own boiling point of 88 C while the gas phase has to be higher and hotter than that because it can only get up to 88 in liquid form
in the distillation apparatus a thermometer positioned too high influence of vapor pressure
thermometer that is too high will have the vapors not enveloping the thermometer bulb completely and the bulb is only partially heated getting a reading of a low temp
during fractional distillation after about 50% of liquid has been distilled from the pot into receiver flasks, the temp shown by thermometer drops, why?
there is barely any of the vapor of the boiling liquid left, while the vapors of the higher boiling liquid have not reached the top of the column. There is not enough vapor to heat the thermometer
why does stirring prevent “bumping” when a strongly heated liquid is at it’s boiling point?
the stirring prevents bumping by keeping the heat distribution maintained it doesn’t boil over and it helps the liquid boil more smoothly by keeping the bubbles controlled. More vigorous it is stirred the less chance of bumping
distillation under vacuum (reduced atmospheric pressure) relative to a distillation at one atmosphere, what is true?
the boiling points of non polar components in the mixture decreases
ensure reproducibility of Rf values is maximized?
atmosphere in TLC chamber, chambers should be closed so solvent in chamber can saturate the atmosphere so molecules are in contact with the silica gel surface
Temp of TLC’s should be developed at 25 C
how can using a pen alter the TLC plate
pens have organic molecules and additional spots may appear
the solvent is higher up than the origin for the TLC plate
origin should be higher or else the sample will dissolve into the solvent reservoir and no spots or streaky spots will be observed
applying to little of a sample to TLC plate
hard to get accurate Rf value and might not enough spots produced
Rf is the inverse of
polarity
so molecules with increasing polarity will have opposite order of increasing Rf
On a TLC plate if one drop of water is at one end and on the other is hexane what will happen
polar and non polar
water won’t spread out but hexane (non polar) will
if they interact they won’t mix well and the nonpolar will go over the polar
are hydrophobic molecules attracted to water?
yes because there is a slight dipole charge, but they don’t go well together
what is true of hydrophobic/non polar liquids
hydrophobic liquids like hexane spread out and form a thin film on polar surfaces (like glass)
hydrophobic liquids rise in capillary (undergo capillary action)
when separating three compounds of medium but different polarity by TLC which of the following factors will make separation occur?
choosing a solvent of medium polarity
creating very small spots at the origin when applying the compound to the plate
what is fluorescence quenching in TLC
it is a technique in which the presence of a compound on a plate is detected by the absence of fluorescence
spots will appear dark on bright background
pka of HI
-10
pka of H2SO4 and HCL
-5
pka of oxinium ions (protonated water, alcohol, and ethers)
0
pka of carboxylic acids
5
pka of phenols, protonated amines, and thiols
10
the pka of water and alcohol
15
pka of amines
35 (uncharged n with h attached)
acidic hydrogen atom in compound A will undergo a proton exchange reaction if
the newly formed bond is less acidc than the bond that was broken in compound A
the proton finds an atom to which it can form a more stable bond
to dry an organic solution and 2 common reagents
means to remove water in our organic solvent layer
reagents = sodium sulfate and magnesium sulfate
you can stop adding the drying agent when it doesnt clump anymore
2 immiscible liquids one is concave one is convex
adhesive and cohesive forces, when the adhesive is stronger than the adhesive then the liquid is concave. When cohesive is stronger than adhesive it will be convex
aqueous HCL
CL + H3O+
when a molecule is hydrophilic and hydrophobic like soap
can interact with grease molecules and form around them called micelles in the hydrophobic area
but when interacted with water it will be emulsified and the grease and oil will be washed away
