Orgo Lab

Which statement is not true?
1.TLC is a good method form monitoring the progress of the reaction
2.Rf value depends on the type of both mobile and stationary phases
3.TLC cannot be used for analyzing colorless compounds
4. More polar mobile phase usually results in higher Rf
value
TLC cannot be used for analyzing colorless compounds
Which solvent as a mobile phase will give the lowest Rf
for given compound?
1) Acetic acid
2) Hexane
3) Methanol
4) Chloroform
5) Impossible to predict
Hexane
Suppose you performed a TLC analysis of ingredients of cold remedies.Instead of getting well de?ned spots you got one long, streaking spot on TLC.
What is the most probable reason for that?
1. Mobile phase was too polar
2. Mobile phase was not polar enough
3. Too much sample was spoTed
4. Solvent front did not travel su?ciently high
5.There was too less solvent (mobile phase) in developing chamber
Too much sample was spotted
Liquid chromatography is a chromatography where:
1. Stationary phase is liquid
2. Mobile phase is liquid
3. Separated substances are liquid
4. All types of chromatography
Mobile phase is liquid
Suppose you are doing column chromatography using dichloromethane as a mobile phase. Then you replaced dichloromethane by methanol. You can expect that:
1. All compounds you are separating will migrate faster
2. All compounds you are separating will migrate slower
3. Only polar compounds will migrate faster
4. Only non?polar compounds will migrate faster
All compounds you are separating will migrate faster
Suppose you did TLC analysis for sample where there was one component. You see the spot at ~ 3 cm from the starting point, and the solvent front is 9 cm from the starting point. The Rf value for this compound is:
1. 9.00
2. 3.00
3. 0.33
4. 0.11
0.33
Which statement is not true?
1.TLC is a good method form monitoring the progress of the reaction
2.Rf value depends on the type of both mobile and stationary phases
3.TLC cannot be used for analyzing colorless compounds
4. More polar mobile phase usually results in higher Rf
value
TLC cannot be used for analyzing colorless compounds
Which of the following could not account for a low recovery of desired compound from
recrystallization:
(1) After dissolving the desired compound in solvent, the resulting solution was cooled down to room temperature not to ice temperature.
(2) Too large volume of solvent was used.
(3) Charcoal has not been used.
(4) Solubility of the desired compound in hot solvent was the same as in cold solvent.
Charcoal has not been used.
Which factor is the least important in choosing proper solvent for recrystallization:
(1) Solvent should not react with recrystallized compound
(2)Solubility of recrystallized compound in given solvent at high temperature should be much higher than the solubility at the room temperature
(3) Solvent should have the proper refractive index to clearly see the shape and size of crystals
(4) Solvent should not have too high boiling point
Solvent should have the proper refractive index to clearly see the shape and size of crystals
Which statement is false:
(1)Meltng point of impure compound is lower than the meltig point of the pure one
(2)Mixture of equal quantities of two di?erent compounds with the same melting points has the same melting point as the pure compounds
(3) Impure compound has a broader melting point range than the pure one
(4) The proper rate of heating the sample for accurate determination of melting point is ~ 2°C/min
)Mixture of equal quantities of two di?erent compounds with the same melting points
2 g of compound X dissolves in 20 mL of water giving saturated solution.
What is a solubility of X in water?
1) 2g/100 mL
2) 5g/100 mL
3) 10g/100 mL
4) 20g/100mL
5)It cannot be calculated without knowing exactly what X is.
5g/100 mL
What can be done to recover compound of interest if too much solvent was used for
recrystallization?
1) Charcoal can be added
2)Solution can be cooled down to very low temperature (near the freezing point of solvent)
3) Solution needs to be cooled down very slowly
4) Some amount of solvent can be distilled o?.
5)Some amount of solvent in which compound of interest has a very low solubility can be added
Solution can be cooled down to very low temperature (near the freezing point of solvent)
Some amount of solvent can be distilled o?.
Some amount of solvent in which compound of interest has a very low solubility can be added
When is the melting point of mixture of two compounds is lowest?
1)When both compounds are in equal amounts in the mixture
2)When mixture composition contains nearly pure compound with the lower melting point
3)At certain mixture composition, characteristic for given pair of compound which is called “eutectic point”
At certain mixture composition, characteristic for given pair of compound which is called “eutectic point”
Gravity Filtration
Used when you want to save a liquid
Vacuum Filtration
Used when you want to save a solid
Liquid-Liquid Extraction
Use for separation of solutes with different solubilities in given solvents. Often used to separate water soluble byproducts from organic material.
Simple Distillation
Used for separation of two or more liquids with different boiling points.
Suppose we have mixture of three compounds.All of them are very well soluble in t- butylmethyl ether (as well as in many other
organic solvents). All of them are insoluble in water. How do we separate them?
We need to selectively convert them into water?soluble derivatives.
We can utilize acid?base properties of the functional groups.
AKA Reactive Acid base extraction
K =
[A] =
K = [A] Organic / [A] aqueous
[A] = mass/ volume -Aqueous aka water stuff
Suppose you have separatory funnel with two phases: aqueous and organic one.
Which statement is true:
(1) Organic phase is always on the top.
(2) Organic phase is always on the bottom
(3) Organic phase with density higher than water is always on the bottom
(4) More polar phase is always on the bottom
(5) Phase added ?rst to the separatory funnel is always on the bottom
Organic phase with density higher than water is always on the bottom
Suppose you have mixture of two compounds A and B and you want to separate
them using extraction. Which pair of solvents would be the best :
(1)The one for which partition coe?cients for both A and B (KA and KB ) are high
(2) The one for which partition coe?cients for both A and B (KA and KB ) are low
(3)The one for which there is big di?erence between KA and KB
(4)The one for which both KA and KB are close to 1.
(3)The one for which there is big di?erence between KA and KB
Based on the pKa table rank the following bases from the strongest to the weakest
Bases: H2O, NaOH, NaHCO3
(1) H2O, NaOH, NaHCO3
(2) NaOH, NaHCO3, H2O
(3) NaOH, H2O, NaHCO3
(4) H2O, NaHCO3, NaOH
(2) NaOH, NaHCO3, H2O
Which statement is correct?
(1) Benzoic acid is soluble in water
(2) Both benzoic acid and 4?t?butylphenol are soluble in 1 M aqueous NaHCO3
(3) Both benzoic acid and 4?t?butylphenol are soluble in 1 M aqueous NaOH
(4) Only 4?t?butylphenol is soluble in 1 M aqueous NaHCO3
Both benzoic acid and 4?t?butylphenol are soluble in 1 M aqueous NaOH
KD is a distribution coe?cient de?ned as concentration of given compound in tertbutyl methyl ether divided by a concentration of given compound in
water, at equilibrium.
Which statement is true:
(1) KD for 1,4?dimethoxybenzene is greater than 1.
(2) KD for benzoic acid is greater than 1
(3) KD for tertbutylphenol is greater than KD for sodium tert?butylphenolate
(4) All above are true
(4) All above are true
What happen when concentrated hydrochloric acid is added to the aqueous solution of sodium benzoate?
(1) pH of the resulting solution decreases.
(2) The added hydrochloric acid shifts the acid dissociation equilibrium in the direction of the nonpolar protonated form of the benzoic acid.
(3) The added hydrochloric acid makes the benzoic acid dissociation constant, Ka, smaller
(4) All above are correct.
(5) Answers (1) and (2) are correct.
5) Answers (1) and (2) are correct.
Why is the amount of sulfuryl chloride used less than the amount theoretically required to convert all the starting material to monosubstituted products?
If at any time during the experiment all of the 1-chlorobutane reactant is completely exhausted, the chlorine radicals could react with the dichlorobutane products to form unwanted products (like tri- or tetra-chlorobutanes). Making sulfuryl chloride the limiting reactant helps to control the rate of the reaction, preventing these unwanted reactions.
Why do you wash solution with NaCL
The bulk of the water can often be removed by shaking or “washing” the organic layer with saturated aqueous sodium chloride (otherwise known as brine). The salt water works to pull the water from the organic layer to the water layer. This is because the concentrated salt solution wants to become more dilute and because salts have a stronger attraction to water than to organic solvents.
why we need to use AIBN for chlorinaion
To start chlorination without needing to heat to really high levels
x

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