Experiment 6: Extraction – Flashcards
Unlock all answers in this set
Unlock answersquestion
Which of the following statements best describes density? -the mass of substance dissolved in a liquid, measured in g/Ml -the amount of substance dissolved in a liquid, measured in mol/L -the mass that a mole of substance has, measured in g/mol -the ration of a substance's mass to its volume, measured in g/mL, and also equivalent to g/cm^3
answer
density is the ratio of a substance's mass to its volume, measured in g/mL, and also equivalent to g/cm^3
question
If a separatory funnel contains two immiscible liquids, dichloromethane (density=1.33 g/mL) and water (density=0.998 g/mL), which substance will be the top layer and which will be the bottom?
answer
Water will be the top layer (less dense) and dichloromethane will be the bottome layer (more dense)
question
a sample of unknown liquid has a mass of A and a volume of B, what is the density of this substance?
answer
density=mass/volume=A/B *remember g/mL is equal to g/cm^3
question
Does density always increase as mass increases?
answer
No, density is independent of mass
question
During a solvent extraction, a student lost track of which layer was the aqueous layer and which was the organic layer. What simple, non-destructive test could be used to determine which layer is which? -add a little distilled water to see which layer the water adds to -obtain a sample of the solution in the separatory funnel and utilize NMR -obtain a sample of the solution in the separatory funnel and utilize IR -ask your instructor if you can perform a super critical extraction on your sample
answer
To determine which layer is aqueous, add a little distilled water to see which layer the water adds to
question
It is known that benzocaine and benzoic acid are significantly more soluble in ethanol than they are in water. Why is ethanol not a suitable solvent for the extraction of benzoic acid and benzocaine from aqueous solution? -benzoic acid and benzocaine both contain polar protic groups -ethanol is miscible with water -ethanol is immiscible in water so the benzoic acid cannot move from one layer to the other -benzocaine and benzoic acid have solubilities in ethanol that are above the usable limit for a solvent extraction
answer
Ethanol is not a suitable solvent because it is miscible with water
question
During a solvent extraction between water and an immiscible solvent, a student has two layers in their separatory funnel and then shakes it. A single, milky liquid develops and no real sign of layers are visible. What has occurred and what should the student do? (chose 2) -pour the mixture into a beaker, reheat, and then try to perform the extraction agin -first, add a small quantity of water, it that does not work, then add solvent -an emulsion has formed -a dilution has occured
answer
An emulsion has formed and the student should first, add a small quantity of water, if that does not work, then add solvent
question
to get effective mixing in a separatory funnel, the combined level of liquids should not exceed: -more than half of the separatory funnel -higher than the stopcock -the lower part of the neck of the separatory funnel -higher than the widest part of the separatory funnel
answer
The liquid level should not be higher than the widest part of the separatory funnel
question
The first step in utilizing a separatory funnel is to make sure the funnel stopcock is closed and then carefully pour the liquid to be extracted into the funnel. True or false?
answer
True
question
The stopcock can be used to vent excess pressure if either of the liquid are warm to the touch and has a low boiling point. True of False?
answer
True
question
Students should throw away the first layer and the acid washes (during experiment 6, the extraction lab). True or False?
answer
False
question
Hold your thumb firmly over the hole in the top of the funnel during shaking. True of False?
answer
False
question
If one is going to re-extract the upper layer with another volume of the liquid, the upper layer can be left in the separatory funnel and fresh solvent added to the funnel. True or False?
answer
True
question
Eugenol, the essential oil found in cloves, is insoluble in water. The alcohol group in eugenol is dramatically more acidic than regular straight-chain alcohols. How could eugenol be separated from a mixture of other non-acidic molecules? -dissolve the mixture in dichloromethane, shake with hydrochloric acid, collect the aqueous layer, and rebasify to force precipitation of the eugenol -dissolve the mixture in dichloromethane, shake with hydrochloric acid, collect the organic layer and evaporate to recover the uegenol -dissolve the mixture in water, shake with dichloromethane, collect the organic layer and evaporate to dryness to revover the eugenol -dissolve the mixture in dichloromethane, shake with sodium hydroxide, collect the aqueous layer, and reacidify to force precipitation of the eugenol
answer
Eugenol can be separated by dissolving the mixture in dichlomethane, shake with sodium hydroxide, collect the aqueous layer, and reacidify to force precipitation of the eugenol
question
Benzoic acid has limited solubility in water, but its conjugate base is completely soluble in water. Draw the structure of the product formed when benzoic acid is treated with aqueous sodium hydroxide. benzoic acid + sodium hydroxide solution --> ?
answer
H2O, Na+, benzene ring with an ester group that has a single bonded O- and a double bonded OH (quiz 6 B)
question
Benzocaine has limited solubility in water, but its conjugate acid is completely soluble in water. Draw the structure of the product formed from the reaction of benzocaine with hydrochloric acid. benzocaine + hydrochloric acid solution -->
answer
Cl-, benzocaine ring with an NH3+ coming off and an ester group with ethane coming off the single bonded O (quiz 6 B)
question
List the procedural steps required to perform a chemically active solvent extraction of a three-component mixture composed of benzoic acid, benzocaine, and a neutral organic molecule all dissolved in dichloromethane
answer
1.)Dissolve the solid three-component mixture in dichloromethane, and place in a separatory funnel. Add 6M HCl to the solution. Shake and allow to settle into layers. 2.)Add water to disolce the brown emulsion between the layers 3.)Separate and collect the aqueous layer in a flask and add base 4.)Place the dichloromethane layer back in the separatory funnel and extract it with 3M NaOH+. Allow layers to settle. 5.)Add water to dissolve the white, gel-like emulsion 6.)Separate and collect the aqueous layer in a flask and add acid 7.)Collect and dry the solids in both erlenmeyer flasks by filtration
question
Why do you add acid to the three component mixture?
answer
To convert the benzocaine into a water soluble salt
question
Why do you vent the separatory funnel through the stopcock
answer
To avoid a build up of pressure inside the glassware
question
Why do you add base to the aqueous acidic layer mixture?
answer
To precipitate the benzocaine
question
Why should you never point the spearatory funnel at anyone including yourself?
answer
To avoid spilling chemicals on yourself and others
question
Classify the following waste as aqueous, solid, chlorinated organic and nonchlorinate organic: sodium hydroxide solution hydrochloric acid solution used pH paper benzoic acid dichloromethane rinse acetone
answer
Aqueous waste: sodium hydroxide solution and hydrochloric acid solution Solid Waste: used pH paper and benzoic acid Chlorinated Organic Waste: dichloromethane Non-chlorinated organic waste: rinse acetone
