Lab C: Separation of Ternary Mixture Using Extraction Technique

Question 1

miscibility definition (and difference with solubility term)

Answer 1

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)

Question 2

relation between miscibility and extraction

Answer 2

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

Question 3

extraction definition and description of setup

Answer 3

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)

Question 4

what is the typical solvent mixture for extraction (with separatory funnel)?

Answer 4

the typical solvent mixture is nonpolar organic + polar aqueous

Question 5

what is the density of water and tBME and dichloromethane (DCM)?

Answer 5

Density of Water: 1.0 g/cm3 = 1.00g/mL
Density of tBMe: 0.74 g/cm3
Density of DCM: 1.33g/mL

Question 6

3 organic compounds used in this experiment

Answer 6

1. benzoic acid: has an COOH functional group and is strongly ACIDIC (pKa = 4.17)
2. 2-naphthol: has an OH functional group (similar to phenol) and weakly ACIDIC (pKa = 9.5)
3. 1,4-dimethoxy benzene: a neutral compound

Question 7

draw out the entire flow chart for the separation of a ternary mixture using extraction technique

Question 8

draw out the entire flow chart for the separation of a carboxylic acid, an amine, and a neutral compound

Question 9

what is the solubility of caffeine in water compared to in dichloromethane (DCM)?

Answer 9

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)

Question 10

draw the chemical molecule for caffeine

Question 11

what are the forces that control solubility?

Answer 11

IMFs (intermolecular forces)
Van der Waals forces
Dipole-Dipole Forces
Hydrogen Bonding

Question 12

what types of molecules are present in the water (aq) layer vs in the organic layer?

Answer 12

Salts, Ionic species – present in Water (Aqueous) Layer
Most Organic Compounds – present in Organic Layer

Question 13

equation for the partition or distribution coefficient? (k)

Answer 13

k = solubility of solute in organic layer/solubility of solute in aqueous layer

Question 14

what is the theory of extraction? (small extractions vs large extractions)

Answer 14

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

Question 15

equation for the percent recovery

Answer 15

% recovery = dry mass of product isolated/initial mass used x 100%

Question 16

separatory funnel basic usage

Answer 16

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

Question 17

what does it mean for a glass stopper to be a 19/22?

Answer 17

19 = width and 22= length in mm

Question 18

stopcock: horizontal position vs vertical position

Answer 18

horizontal position: closed to drain (cannot drain)
vertical: open to drain

Question 19

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?

Answer 19

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)

Question 20

use which type of funnel to add solutions into the separatory funnel?

Answer 20

pyrex funnel (long funnel) - for liquids

Question 21

when venting the separatory funnel, where should you point it?

Answer 21

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

Question 22

why does pressure build up in the separatory funnel?

Answer 22

due to the formation of CO2 gas

Question 23

4 key knowledge points about densities for extraction

Answer 23

• 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

Question 24

what are drying agents (anhydrous salts)? give one example

Answer 24

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)

Question 25

differences between gravity filtration and vacuum filtration

Answer 25

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

Question 26

what are the 5 components of a rotary evaporator and definition?

Answer 26

definition: a device used to remove solvents from samples through evaporation components - heating bath - condenser - rotary motor - solvent collection flask - vacuum source

Question 27

facts to know about how a rotary evaporator works

Answer 27

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)

Question 28

what are 3 precautionary measures when using a rotary evaporator?

Answer 28

1. Do not use a round bottom flask with any visible cracks or star cracks 2. 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 3. Do not use a broken blue keck clip. If you do, your round bottom flask will slip into the hot water bath

Question 29

what are emulsions and how do they form?

Answer 29

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)

Question 30

what can you do to get rid of an emulsion?

Answer 30

- 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

Question 31

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)

Answer 31

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

Question 32

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?

Answer 32

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

Question 33

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?

Answer 33

benzoic acid (s, acid) + NaHCO3 (aq, base) --> sodium benzoate (aq, conjugate base) + H2O (l, conjugate acid) + CO2 (g)

Question 34

describe liquid-liquid extraction

Answer 34

typically performed using 2 IMMISCIBLE solvents: one polar, one nonpolar polar - usually water nonpolar - usually diethyl ether (EtO2)

Question 35

how do you separate compounds using extraction?

Answer 35

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)

Question 36

compare and contrast the three compounds: 1. benzoic acid 2. 2-napthol 3. p-dimethoxybenzene

Answer 36

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

Question 37

what compound does the first extraction extract? what compound does the second extraction extract? what compound does the third extraction extract?

Answer 37

1. benzoic acid (using weak base NaHCO3) 2. 2-napthol (using strong base NaOH) 3. p-dimethoxybenzene (only compound left --> so just drain out of sep funnel)

Question 38

describe why it is possible to extract the three compounds by using acid-base reactions

Answer 38

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

Question 39

describe the appearance of benzoic acid, 2-napthol, and p-dimethoxybenzene (aka the solids in the beginning of lab)

Answer 39

benzoic acid: white solid (pellets) 2-napthol: light brown solid p-dimethoxybenzene: shiny white solid (more crystal-like)

Question 40

the gas bubbles resulting from shaking the sep funnel happens with which reaction/compounds?

Answer 40

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

Question 41

what could happen if you do NOT shake the sep funnel vigorously enough after adding sodium bicarbonate NaHCO2?

Answer 41

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

Question 42

describe the overall procedure for the extraction of both benzoic acid and 2-napthol

Answer 42

1. treat with sodium bicarbonate NaHCO2 (for benzoic acid) or sodium hydroxide NaOH (for 2-napthol) and extract from sep funnel 2. add HCl into both and wait until the pH of the solutions is acidic (pH paper is PINK) 3. vacuum filtration to collect the solids

Question 43

describe the overall procedure for the extraction of p-dimethoxybenzene

Answer 43

1. after both benzoic acid and 2-napthol have been extracted, drain the sep funnel to collect the leftover p-DMB 2. add drying agent (anhydrous CaCl2 pellets) to the solution to remove any traces of the aqueous layer 3. gravity filtration to separate the solid drying agents from the p-DMB 4. rotary evaporation: the white solid will appear coated on the walls of the round bottom flask

Question 44

describe the appearance of benzoic acid and 2-napthol precipitates after adding HCl to them

Answer 44

benzoic acid: heavy white precipitate 2-napthol: pink brown precipitate

Question 45

how do you clean the 3 125mL erlenmeyer flasks and all used grad cylinders?

Answer 45

clean first with 2-3mL of acetone and then rinse with tap water

Question 46

where do you dispose of used/waste acetone?

Answer 46

in a container labeled "Acetone rinsings"

Question 47

describe the appearance of the 3 compounds after complete extraction/lab over

Answer 47

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)

Question 48

what is the pKa values for benzoic acid and 2-napthol?

Answer 48

Benzoic acid: pKa = 4.17 (strong acid) 2-napthol: pKa = 9.5 (weak acid)

Question 49

relationship between pKa value and acid strength?

Answer 49

lower pKa value = stronger acid (inversely related)

Question 50

venting defintiion

Answer 50

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)

Question 51

what are the hazards for... 1. benzoic acid 2. 1,4-DMB 3. 2-naphthol 4. sodium benzoate 4. sodium naphthoxide 5. HCl

Answer 51

Benzoic acid & 1,4 DMB: corrosive TMB: flammable & corrosive 2-naphthol: toxic Sodium benzoate: irritant Naphthoxide: toxic HCl: corrosive

Question 52

when could a single extraction (instead of multiple smaller ones) be okay?

Answer 52

when partition coefficient k is large

Question 53

Any organic compound with a ___ (k value of what) can be separated from water by extraction with a water-insoluble organic solvent

Answer 53

Any organic compound with a K > 1.5 can be separated from water by extraction with a water-insoluble organic solvent

Question 54

relation between conjugate base stability and acid strength?

Answer 54

conjugate base stability increase = acid strength increase Look at conjugate base for more stable (resonance for double bond O) = stronger acid

Question 55

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

Question 56

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?

Answer 56

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