Lab C: Separation of a ternary mixture using the extraction technique

Question 1

What does it mean for two liquids to be miscible? Given an example

Answer 1

When two liquids are “miscible,” it means they can mix completely with each other in any proportion.

Example: acetone and water

Question 2

You must have two ________ liquids to carry out a liquid-liquid extraction

Answer 2

immiscibleone polar and one non-polar

Question 3

What does it mean for two liquids to be immiscible?

Answer 3

When two liquids are “immiscible,” it means they cannot mix together and will separate into distinct layers when combined

Question 4

Draw a schematic that shows the extraction technique in a separator funnel

Answer 4

Drawn in notes

Question 5

What is the typical solvent mixture in speratory funnels?

Answer 5

Non polar organic + polar aqueous

Question 6

The layers settle depending on their

Answer 6

densities, with the more dense solvent sinking to the bottom. the less dense solvent floats tot he top

Question 7

What is the density of water

Answer 7

1.0 g/cm3

Question 8

What is the density of tBME

Answer 8

0.74 g/cm3

Question 9

draw the three organic compounds used in this experiment. Label them as strongly acidic, weakly acidic, and neutral.

Answer 9

Drawn in notes

Question 10

What is the pKa of Benzoic acid?

Answer 10

4.17(strong acid)

Question 11

Why is the pKa of 2-napthol?

Answer 11

9.5(weak acid)

Question 12

Draw the full flow chart

Answer 12

refer to lab notebook

Question 13

Compounds partition between two layers based on relative solubility. What are the forces that control solubility?

Answer 13

van der Waals forces

dipole-dipole forces

hydrogen bonding

Question 14

What substances will be present in the water(aqueous) layer?

Answer 14

salt, ionic species

Question 15

What substances will be present in the organic layer?

Answer 15

Most organic compounds

Question 16

What is the theory of extraction

Answer 16

It is always better to do several smaller extractions than one big extraction. This maximizes the amount of material extracted, and in turn increases theoretical recovery

Question 17

What is percent recovery

Answer 17

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

Question 18

What are emulsions?

Answer 18

A suspension of immiscible droplets of one liquid in another liquid

Results in a loss of two distinct phases

Question 19

How do emulsions form?

Answer 19

Sometimes, shaking the sparatory funnel too vigourously leads to an emulsion. However, shaking the separator funnel too gently either, may not give you an effective mixing of the two phases

Question 20

What can you do to get rid of an emulsion?

Answer 20

Allow the separators 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 21

Draw the schematic for a separator funnel

Answer 21

Refer to notes

Question 22

What is a pyrex funnel used for?

Answer 22

pouring liquids, long stem funnel

Question 23

What are drying agents

Answer 23

Anhydrous salts(devoid of water) that combine with the water that is mixed in with your product, and retains it as water of crystallization

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 RBF, leaving the hydrated salts on the filter paper

Question 24

Draw the schematic for a gravity filtration

Answer 24

refer to notes

Question 25

Draw the schematic for a vacuum filtration

Answer 25

Refer ot notes

Question 26

What is a rotary evaporator

Answer 26

A rotary evaporator, often called a "rotovap", is a laboratory device used to efficiently remove solvents from samples by evaporation under reduced pressure. the rotary evaporator will evaporate the solvent under vacuum and the neutral compound will appear as a solid coated on the walls of the RBF.

Question 27

Why does the rotovap spin the RBF?

Answer 27

Increase the surface area covered by the solvent

Question 28

In the rotovap, applying vacuum reduces

Answer 28

boiling point of the solvent being removed

Question 29

Label the diagram of the rotary evaporator

Answer 29

Refer to slides

Question 30

When is gravity filtration used? What type of funnel does it use?

Answer 30

Gravity filtration is used when solute is mixed with a low-boiling point solvent. It is used to filter during agents such as anhydrous CaCl2 and anhydrous MgSO4 It employs a powder funnel

Question 31

What is the literature melting point range of salicylic acid?

Answer 31

158-161 degrees celsius

Question 32

Explain how the extraction technique works

Answer 32

When a mixture of compounds is shaken in the stoppered separator funnel with he two solvents, any polar compounds and/or inorganic salts will dissolve in the polar solvent, and likewise the non polar compounds will dissolve in the non-polar solvent. In this way, it is possible to extract a compound(or some impurity) from one solvent into the other. Since the solvents do not mix with each other, they will form layers based on their density and can be separated by first draining the bottom layer out of the separator funnel and later draining the left over top layer out of the separator funnel. The desired compound is usually recovered in pure form from the layer it was dissolved in by simply evaporating the solvent(typically using a rotary evaporator)

Question 33

Explain why 2-napthol is an acid

Answer 33

The conjugate base of 2-napthol is stabilized by virtue of the pi-bonds in the rings. Several resonance structures can be drawn which delocalize the negative charge on the conjugate base and thus increase the acidity of 2-napthol.

Question 34

Does 2-napthol need to be deptronated with a strong or weak base?

Answer 34

strong base such ad NaOH cannot be deprotnated by a weaker base such as sodium bicarbonate(NaHCO3)

Question 35

Does benzoic acid need to be deprotnated by a strong or weak base

Answer 35

Because it is significantly more acidic than 2-napthol, benzoic acid can be deprotnated but the weak base NaHCO3

Question 36

Explain the entire separation process for this lab

Answer 36

1. the three compounds are dissolved in an organic solvent --> tBME 2. The conjugate bases of each acid are much more poor species and are thus water-soluble 3. Using an aqueous solution of the weak base sodium bicarbonate(NaHCO3), we can remove benzoic acid from the organic layer into the aqueous layer(as its polar salt), leaving the 2-napthol and p-DMB behind in the organic layer The benzoic acid can then be recovered from the aqueous layer by adding a strong acid like conc. hydrochloric acid. The sodium salt of benzoic acid can then be protonated to regenerate benzoic acid which can be collected by carrying out a vacuum filtration. 4. The 2-napthol can then be separated from p-DMB present in the organic layer(tBME) by extraction using an aqueous solution of a stronger base, NaOH. This is followed by acidifying the solution with conc. Hal to regenerate 2-napthol, which can then be collected by carrying out a vacuum filtration. 5. The neutral component, p-dimethoxybenzene present in the separator funnel along with the tBMW is drained and treated with an anhydrous drying agent to remove any traces of aqueous material, followed by doing a gravity filtration in a reweighed RBF. p-dimethoxybenzene is recovered through a rotary evaporator.

Question 37

What is the hazard associated with tBME

Answer 37

flammable and an irritant

Question 38

what is the hazard associated with benzoic acid, 2-naphthol and p-dimethoxybenzene

Answer 38

irritants

Question 39

What are the hazards associated with sodium hydroxide and hydrochloric acid

Answer 39

corrosive and toxic

Question 40

What are the colours of each of the three solids in the beginning of this experiment

Answer 40

Benzoic acid: white solid 2-Napthol: light brown solid p-DMB: shiny white solidWha

Question 41

What type of funnel is used to transfer the tBME

Answer 41

pyrex

Question 42

After the NaHCO3 has been added, what is in the bottom vs top layer and what are the colours of each layer?

Answer 42

Top: organic and clear bottom: aqueous, yellow

Question 43

At which step of the operation process is venting required?

Answer 43

After adding the NaHCO3 since co2 is produced

Question 44

when the aqueous layer is drained, what is being extracted?

Answer 44

sodium benzoate

Question 45

Why is shaking important?

Answer 45

NaHCO3 s a weak base and we want to give it the best shot of deprotonating the benzoic acid

Question 46

Is venting required with the NaOH is added?

Answer 46

no

Question 47

After the NaOH is added, what is in the top vs bottom layer and what are the colors?

Answer 47

top layer: organic(containing tBME and DMB), clear & yellow aqueous layer: sodium salt of 2-naphthol, light brown

Question 48

When the conc. HCL s added to each of the extracts, what is the appearance of the precipitate? How are these precipitates then isolated?

Answer 48

Bicarbonate: thick, white, fluffy precipitate Hydroxide: brownish pink solid precipitates are placed in an ice bath and a vacuum filtration s done

Question 49

What do you do with the acidic filtrates?

Answer 49

put into the container labeledd "Waste acidic filtrates - extraction lab:"

Question 50

What do you do with the drying agent

Answer 50

put in biohazard box

Question 51

where do all glass pipettes go?

Answer 51

sharps container

Question 52

how is the DMB isolated?

Answer 52

use a gravity filtration to remove the drying agent and then do a rotary evaporation.

Question 53

What was the final appearance of everything once it was extracted and isolated?

Answer 53

DMB: orange gel like substance Benzoic acid: white flakes 2-naphthol: pale pink clump

Question 54

What is the density of tBME

Answer 54

0.74

Question 55

Which is more polar, benzoic acid or sodium benzoate? Explain which of the above two compounds is more likely to dissolve in water?

Answer 55

Sodium benzoate is more poor because it has a water-soluble Na+ ions(i.e. it is an ionic compound), allowing the molecule to create a stronger dipole moment. The polar nature makes it more likely to dissolve in water.