Lab C: Separation of Ternary Mixture Using Extraction Technique Flashcards
miscibility definition (and difference with solubility term)
miscibility: the ability of 2 liquids to mix completely to form a homogeneous solution (2 liquids)
solubility: the ability for a solid to dissolve in a liquid (1 liquid, 1 solid)
relation between miscibility and extraction
miscible liquid pairs are NOT suitable for extraction; you must have two IMMISCIBLE liquids to carry out a liquid-liquid extraction
miscible liquid example: acetone with water
extraction definition and description of setup
A technique used for the isolation and purification of organic compounds based on the SOLUBILITY DIFFERENCES between compounds
–> the compounds partition between 2 layers based on relative solubilities
the layers settle depending on their DENSITIES: the MORE dense solvent sinks to the BOTTOM; the LESS dense solvent floats to the TOP
using a separatory funnel: glass stopper, a stopcock, stem
an extraction may involve amines mixed in with an acid and base (amines: R-NH2)
what is the typical solvent mixture for extraction (with separatory funnel)?
the typical solvent mixture is nonpolar organic + polar aqueous
what is the density of water and tBME and dichloromethane (DCM)?
Density of Water: 1.0 g/cm3 = 1.00g/mL
Density of tBMe: 0.74 g/cm3
Density of DCM: 1.33g/mL
3 organic compounds used in this experiment
- benzoic acid: has an COOH functional group and is strongly ACIDIC (pKa = 4.17)
- 2-naphthol: has an OH functional group (similar to phenol) and weakly ACIDIC (pKa = 9.5)
- 1,4-dimethoxy benzene: a neutral compound
draw out the entire flow chart for the separation of a ternary mixture using extraction technique
draw out the entire flow chart for the separation of a carboxylic acid, an amine, and a neutral compound
what is the solubility of caffeine in water compared to in dichloromethane (DCM)?
water: most organics are insoluble (organics are usually nonpolar but water is polar)
- solubility of caffeine: 2.2g/100mL at 25C
DCM (CH2Cl2): polar organic solvent
- solubility of caffeine: 10.2g/100mL at 25C (since caffeine is POLAR ORGANIC compound)
draw the chemical molecule for caffeine
what are the forces that control solubility?
IMFs (intermolecular forces)
Van der Waals forces
Dipole-Dipole Forces
Hydrogen Bonding
what types of molecules are present in the water (aq) layer vs in the organic layer?
Salts, Ionic species – present in Water (Aqueous) Layer
Most Organic Compounds – present in Organic Layer
equation for the partition or distribution coefficient? (k)
k = solubility of solute in organic layer/solubility of solute in aqueous layer
what is the theory of extraction? (small extractions vs large extractions)
it is always better to do several smaller extractions than one big extraction.
- To maximize the amount of material extracted, and in turn to increase the theoretical recovery
equation for the percent recovery
% recovery = dry mass of product isolated/initial mass used x 100%
separatory funnel basic usage
The separatory funnel used is a 125 mL
with a 19/22 standard taper joint.
Glass stopper must be also be a 19/22
- Remember to remove the glass stopper
from the top of the separatory funnel before
draining the solution
shake the contents of the separatory funnel and then wait to allow the layers to separate to observe relative densities
what does it mean for a glass stopper to be a 19/22?
19 = width and 22= length in mm
stopcock: horizontal position vs vertical position
horizontal position: closed to drain (cannot drain)
vertical: open to drain
what should the stopcock be (closed or opened) when adding solutions into the separatory funnel?
what should the stopcock be (closed or opened) and glass stopper be when draining the solution?
the stopcock is CLOSED when adding solutions into the separatory funnel
- Remember to remove the glass stopper
from the top of the separatory funnel before
draining the solution (otherwise, the funnel will not drain)
use which type of funnel to add solutions into the separatory funnel?
pyrex funnel (long funnel) - for liquids
when venting the separatory funnel, where should you point it?
Always vent your funnel inside the fume hood with the stem of the funnel pointing away from you and your neighbors
point the separatory funnel toward the back of the hood when venting
why does pressure build up in the separatory funnel?
due to the formation of CO2 gas
4 key knowledge points about densities for extraction
- An aqueous solution will typically have a density of ≈ 1
g/mL - The more dense layer will always be on the bottom
- Organic solvents that are LESS dense than water form the upper layer in the separatory funnel, and solvents that are denser will form the lower layer
- In general, aqueous solutions (acidic, basic or neutral) are IMMISCIBLE with organic solvents such as ether, hexane & methylene chloride
what are drying agents (anhydrous salts)? give one example
Anhydrous salts (without water) that combine
with the water that is mixed in with your product, and
retains it as water of crystallization
- when drying agents are first added, they clump together but after enough is added, it becomes free floating
When all the water is bound with the salt, we
gravity-filter the mixture
- The liquid (now free of water) passes through the gravity filter paper into your pre-weighed round bottom flask, leaving the hydrated salts on the filter paper
example: anhydrous calcium chloride (CaCl2)
differences between gravity filtration and vacuum filtration
gravity filtration:
- used when solute is mixed with a LOW BOILING solvent
- DCM (CH2Cl2), diethyl ether
- used to filter drying agents (ie. anhydrous CaCl2, anhydrous MgSO4)
- uses a POWDER FUNNEL
vacuum filtration:
- used when solute is mixed with high-boiling organic (alcohol and hydrocarbon solvents) and water
- uses a BUCHNER FUNNEL
choose gravity filtration over vacuum filtration when you use a LOW BOILING SOLVENT
what are the 5 components of a rotary evaporator and definition?
definition: a device used to remove solvents from samples through evaporation
components
- heating bath
- condenser
- rotary motor
- solvent collection flask
- vacuum source
facts to know about how a rotary evaporator works
The rotovap spins the round bottom flask to INCREASE the surface area covered by the solvent
Applying vacuum REDUCES the boiling point of the solvent being removed
Spinning flask helps prevent solvent from bumping
(Bumping happens when a liquid boils suddenly and violently, causing large bubbles to burst and possibly splashing the solution into the condenser or outside the flask)
what are 3 precautionary measures when using a rotary evaporator?
- Do not use a round bottom flask with any visible cracks or star cracks
- The round bottom flask should not be more than half-full. If it is, the solvent along with product will spill over
into the solvent bump trap - Do not use a broken blue keck clip. If you do, your round bottom flask will slip into the hot water bath
what are emulsions and how do they form?
emulsions: a suspension of immiscible droplets of one liquid in another liquid –> results in a loss of two distinct phases
how do emulsions form?
–> Sometimes, shaking the Separatory Funnel too vigorously leads to an emulsion. However, shaking the separatory funnel too gently as well, may not give you an effective mixing of the two phases
(aka shaking too hard or not shaking hard enough)
what can you do to get rid of an emulsion?
- Allow the separatory funnel to sit undisturbed in the ring clamp for a couple of minutes
- Stir the emulsion interface with a glass rod
- Add a little salt
Which is more polar, benzoic acid or sodium benzoate Explain which of the above two compounds is more likely to dissolve in water (use their chemical structures to explain your answer)
sodium benzoate (has a carboxylate ion + Na+) is more polar than benzoic acid (has a COOH group) since there is a large dipole created by the Na+ ions compared to the polar COVALENT bonds on benzoic acid
–> sodium benzoate is more likely to dissolve in water
what is…
- the density of water (show units).
- the density of tert-Butyl methyl ether (show units)
Based on the above density values, which solvent layer will be the top layer?
density of water: 0.9970g/mL at 25C
density of t-BME: 0.74g/mL at 25C
–> tBME will be the top layer since it is LESS dense
In this extraction lab, you use solid benzoic acid and a 15% aqueous solution of sodium bicarbonate.
a. Draw a balanced chemical reaction for the reaction between the above two components; what are the phases of each?
benzoic acid (s, acid) + NaHCO3 (aq, base) –> sodium benzoate (aq, conjugate base) + H2O (l, conjugate acid) + CO2 (g)
describe liquid-liquid extraction
typically performed using 2 IMMISCIBLE solvents: one polar, one nonpolar
polar - usually water
nonpolar - usually diethyl ether (EtO2)
how do you separate compounds using extraction?
when you SHAKE the mixture of compounds in the stoppered separatory funnel with the two different solvents (one polar, one nonpolar), the polar and inorganic compounds will dissolve in the polar solvent and the nonpolar/organic compounds will dissolve in the nonpolar solvent
–> since the two solvents are immiscible, you can separate the compounds by draining out the solvent (first bottom layer) to remove/extract the first compound in the first bottom layer of the sep funnel
–> the desired compound is then recovered back into pure form from the solvent it was dissolved in by simply evaporating the solvent (using a ROTARY EVAPORATOR)
compare and contrast the three compounds:
1. benzoic acid
2. 2-napthol
3. p-dimethoxybenzene
benzoic acid: STRONG acid
- can be deprotonated with a WEAKER BASE (aka sodium bicarbonate NaHCO3)
- is a carboxylic acid and is thus significantly more acidic than 2-napthol
2-napthol: WEAK acid
- similar to an alcohol in that both have an OH group attached to a C BUT the conjugate base of 2-napthol is RESONANCE stabilized by the pi-bonds in the rings
- can be deprotonated with a STRONG BASE (aka sodium hydroxide NaOH) to form a water-soluble salt
p-dimethoxybenzene: NEUTRAL
what compound does the first extraction extract?
what compound does the second extraction extract?
what compound does the third extraction extract?
- benzoic acid (using weak base NaHCO3)
- 2-napthol (using strong base NaOH)
- p-dimethoxybenzene (only compound left –> so just drain out of sep funnel)
describe why it is possible to extract the three compounds by using acid-base reactions
all 3 compounds in their normal form are soluble in an ORGANIC solvent (ie. tBME)
HOWEVER, the CONJUGATE BASES of each of the 3 acids are much MORE POLAR and thus WATER SOLUBLE
describe the appearance of benzoic acid, 2-napthol, and p-dimethoxybenzene (aka the solids in the beginning of lab)
benzoic acid: white solid (pellets)
2-napthol: light brown solid
p-dimethoxybenzene: shiny white solid (more crystal-like)
the gas bubbles resulting from shaking the sep funnel happens with which reaction/compounds?
sodium bicarbonate NaHCO2 that is added and which reacts with benzoic acid –> one of the byproducts is carbon dioxide CO2 –> which is why you need to VENT when shaking for this reaction
do not need to vent when shaking for the reaction between NaOH + 2-napthol
what could happen if you do NOT shake the sep funnel vigorously enough after adding sodium bicarbonate NaHCO2?
you may not extract all of the benzoic acid from the tBME layer into the water layer and thus when you add HCl to the bicarbonate layer later collected in the erlen flask, you will not get a precipitate
describe the overall procedure for the extraction of both benzoic acid and 2-napthol
- treat with sodium bicarbonate NaHCO2 (for benzoic acid) or sodium hydroxide NaOH (for 2-napthol) and extract from sep funnel
- add HCl into both and wait until the pH of the solutions is acidic (pH paper is PINK)
- vacuum filtration to collect the solids
describe the overall procedure for the extraction of p-dimethoxybenzene
- after both benzoic acid and 2-napthol have been extracted, drain the sep funnel to collect the leftover p-DMB
- add drying agent (anhydrous CaCl2 pellets) to the solution to remove any traces of the aqueous layer
- gravity filtration to separate the solid drying agents from the p-DMB
- rotary evaporation: the white solid will appear coated on the walls of the round bottom flask
describe the appearance of benzoic acid and 2-napthol precipitates after adding HCl to them
benzoic acid: heavy white precipitate
2-napthol: pink brown precipitate
how do you clean the 3 125mL erlenmeyer flasks and all used grad cylinders?
clean first with 2-3mL of acetone and then rinse with tap water
where do you dispose of used/waste acetone?
in a container labeled “Acetone rinsings”
describe the appearance of the 3 compounds after complete extraction/lab over
Products
Sodium benzoate: white and powdery (vacuum)
Sodium Naphthoxide: pinkish brown clay like (vacuum)
1,4-dimethoxybenzene: gravity filtration & rotovap (white and sticking on sides of RB)
what is the pKa values for benzoic acid and 2-napthol?
Benzoic acid: pKa = 4.17 (strong acid)
2-napthol: pKa = 9.5 (weak acid)
relationship between pKa value and acid strength?
lower pKa value = stronger acid (inversely related)
venting defintiion
Venting - pressure builds in funnel due to formation of CO2 gas (makes sense if you look at the reaction for benzoic acid + NaHCO3 –> sodium benzoate + H2O + CO2)
what are the hazards for…
1. benzoic acid
2. 1,4-DMB
3. 2-naphthol
4. sodium benzoate
4. sodium naphthoxide
5. HCl
Benzoic acid & 1,4 DMB: corrosive
TMB: flammable & corrosive
2-naphthol: toxic
Sodium benzoate: irritant
Naphthoxide: toxic
HCl: corrosive
when could a single extraction (instead of multiple smaller ones) be okay?
when partition coefficient k is large
Any organic compound with a ___ (k value of what) can be separated from water by extraction with a water-insoluble organic solvent
Any organic compound with a K > 1.5 can be separated from water by extraction with a water-insoluble organic solvent
relation between conjugate base stability and acid strength?
conjugate base stability increase = acid strength increase
Look at conjugate base for more stable (resonance for double bond O) = stronger acid
solid benzoic acid and a 15% aqueous solution of sodium bicarbonate
a. Draw a balanced chemical reaction for the reaction between the above two components.
b. Label the acid and the base on the left side of the equation and the conjugate acid and conjugate
base on the right side of the equation.
c. Label the phases for all compounds involved in this equation as either (s) for solid, (aq) for aqueous,
(l) for liquid, and (g) for gas
Which is more polar, benzoic acid or sodium benzoate? Draw both the structures.
Explain which of the above two compounds is more likely to dissolve in water?
sodium benzoate is more polar since it is an ionic salt, which means there is a large difference in electronegativity between the negative O- and positive Na+ ions
Sodium benzoate is more likely to dissolve in water because “like dissolves like” and water is polar
