Lab C: Separation of a ternary mixture using the extraction technique Flashcards
What does it mean for two liquids to be miscible? Given an example
When two liquids are “miscible,” it means they can mix completely with each other in any proportion.
Example: acetone and water
You must have two ________ liquids to carry out a liquid-liquid extraction
immiscibleone polar and one non-polar
What does it mean for two liquids to be immiscible?
When two liquids are “immiscible,” it means they cannot mix together and will separate into distinct layers when combined
Draw a schematic that shows the extraction technique in a separator funnel
Drawn in notes
What is the typical solvent mixture in speratory funnels?
Non polar organic + polar aqueous
The layers settle depending on their
densities, with the more dense solvent sinking to the bottom. the less dense solvent floats tot he top
What is the density of water
1.0 g/cm3
What is the density of tBME
0.74 g/cm3
draw the three organic compounds used in this experiment. Label them as strongly acidic, weakly acidic, and neutral.
Drawn in notes
What is the pKa of Benzoic acid?
4.17(strong acid)
Why is the pKa of 2-napthol?
9.5(weak acid)
Draw the full flow chart
refer to lab notebook
Compounds partition between two layers based on relative solubility. What are the forces that control solubility?
van der Waals forces
dipole-dipole forces
hydrogen bonding
What substances will be present in the water(aqueous) layer?
salt, ionic species
What substances will be present in the organic layer?
Most organic compounds
What is the theory of extraction
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
What is percent recovery
% recovery = (mass of product isolated / initial mass used) x 100%
What are 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 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
What can you do to get rid of an emulsion?
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
Draw the schematic for a separator funnel
Refer to notes
What is a pyrex funnel used for?
pouring liquids, long stem funnel
What are drying agents
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
Draw the schematic for a gravity filtration
refer to notes
Draw the schematic for a vacuum filtration
Refer ot notes
What is a rotary evaporator
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.
Why does the rotovap spin the RBF?
Increase the surface area covered by the solvent
In the rotovap, applying vacuum reduces
boiling point of the solvent being removed
Label the diagram of the rotary evaporator
Refer to slides
When is gravity filtration used? What type of funnel does it use?
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
What is the literature melting point range of salicylic acid?
158-161 degrees celsius
Explain how the extraction technique works
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)
Explain why 2-napthol is an acid
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.
Does 2-napthol need to be deptronated with a strong or weak base?
strong base such ad NaOH
cannot be deprotnated by a weaker base such as sodium bicarbonate(NaHCO3)
Does benzoic acid need to be deprotnated by a strong or weak base
Because it is significantly more acidic than 2-napthol, benzoic acid can be deprotnated but the weak base NaHCO3
Explain the entire separation process for this lab
- the three compounds are dissolved in an organic solvent –> tBME
- The conjugate bases of each acid are much more poor species and are thus water-soluble
- 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.
- 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.
- 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.
What is the hazard associated with tBME
flammable and an irritant
what is the hazard associated with benzoic acid, 2-naphthol and p-dimethoxybenzene
irritants
What are the hazards associated with sodium hydroxide and hydrochloric acid
corrosive and toxic
What are the colours of each of the three solids in the beginning of this experiment
Benzoic acid: white solid
2-Napthol: light brown solid
p-DMB: shiny white solidWha
What type of funnel is used to transfer the tBME
pyrex
After the NaHCO3 has been added, what is in the bottom vs top layer and what are the colours of each layer?
Top: organic and clear
bottom: aqueous, yellow
At which step of the operation process is venting required?
After adding the NaHCO3 since co2 is produced
when the aqueous layer is drained, what is being extracted?
sodium benzoate
Why is shaking important?
NaHCO3 s a weak base and we want to give it the best shot of deprotonating the benzoic acid
Is venting required with the NaOH is added?
no
After the NaOH is added, what is in the top vs bottom layer and what are the colors?
top layer: organic(containing tBME and DMB), clear & yellow
aqueous layer: sodium salt of 2-naphthol, light brown
When the conc. HCL s added to each of the extracts, what is the appearance of the precipitate? How are these precipitates then isolated?
Bicarbonate: thick, white, fluffy precipitate
Hydroxide: brownish pink solid
precipitates are placed in an ice bath and a vacuum filtration s done
What do you do with the acidic filtrates?
put into the container labeledd “Waste acidic filtrates - extraction lab:”
What do you do with the drying agent
put in biohazard box
where do all glass pipettes go?
sharps container
how is the DMB isolated?
use a gravity filtration to remove the drying agent and then do a rotary evaporation.
What was the final appearance of everything once it was extracted and isolated?
DMB: orange gel like substance
Benzoic acid: white flakes
2-naphthol: pale pink clump
What is the density of tBME
0.74
Which is more polar, benzoic acid or sodium benzoate?
Explain which of the above two compounds is more likely to dissolve in water?
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.
