QUI_01_ Physico-chemical assays of solids
AF Unit 3: Advanced physico-chemical experiments
3.1 Writing a lab report
Source: pt.wikipedia.org
After an experiment, your boss may ask you to present a lab report explaining the experiment,
its results, and the conclusions of your work. The structure of a lab report can be very different
depending on the place you end up working, but it’s important that you are able to report your
results correctly.
HIGHLIGHTS
Lab reports may have different structures. In this unit, we’ll consider the following structure:
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Title, date
Aim of the experiment
Security measures and PPE (personal protective equipment)
Results and observations
Calculations
Conclusion
Waste management
Bibliography
QUI_01_ Physico-chemical assays of solids. / Unit 3
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TO KNOW MORE
Depending on your English level, you may find it difficult to write some of the sections of the
lab report. Check the following document if you need help to write your conclusions:
Language support – writing conclusions
Task 1: Another section of the lab report that is sometimes difficult to write correctly is
the aim of the experiment. In this activity, you have some sentences that you can adapt
to write you experiment’s aim.
Match two of the following phrases (one from each box) to create correct sentences
describing aims of lab experiments:
1. The aim of the experiment is to determine...
2. The aim of the experiment is to investigate the effects of…
3. The aim of the experiment is to verify…
4. The aim of the experiment is to determine the relationship…
a) between the pH of the dissolution and the color of the substance.
b) kirchoff’s voltage law.
c) temperature in the dissolution rate when solving salt in water.
d) the exact melting point of a solid sample.
Write down the correct aims of the experiments:
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TO KNOW MORE
In one of the sections of your lab report, you have to write down what PPE are necessary to
carry out your experiment. If you don’t know the names of the PPE in English, check the
following document:
PPE selection guide by Hardvard University
3.2 Liquid-liquid extraction. Determination of the partition constant
In units one and two, we have studied the
factors affecting the solubility of solid
substances in one solvent. Now, we are
going to study a more complex process: the
liquid-liquid extraction, in which the solid
substance will be solved in two immiscible
solvents.
Source: commons.wikipedia.org
HIGHLIGHTS
Liquid-liquid extraction is a method to separate substances based on their relative solubilities
in two different immiscible liquids, usually water and an organic solvent.
First of all, let’s learn how to perform a liquid-liquid extraction correctly. The process is explained
in the following video. If it’s difficult for you to understand the video, you can always activate the
youtube subtitles by pressing the “CC” button under the video.
Liquid-liquid extraction
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Task 2: In this task, we are going to prepare an ED-puzzle, which is a video that stops
several times during its duration to present questions about the content of the video.
You have to prepare an ED-Puzzle introducing at least 5 questions in the video. The
video in which you have to introduce the questions is the same you have watched before
about liquid to liquid extraction. Work in pairs.
When you are done, share your ED-puzzle with other couples through email. Afterwards,
try to solve some of your partner’s ED-puzzles.
Make any video your lesson with ED-puzzle.
LANGUAGE SUPPORT: Go back to Unit 1 if you need help to write questions in English
(Unit 1, page 5). Here you have some other question structures that might be helpful in
this task:
Language support: Question structures. Examples:
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Why do we check the stopcock….?
How should the funnel be shaken ?
Why do we keep the funnel inverted during…..?
How do we relieve the pressure……. ?
How long should we shake……..?
What should we do after the two layers have settled?
Why do we place the end of the glass tube on the side of
the……???
3.3 Liquid-liquid extraction. Determination of the partition constant
After the extraction process, the solute portioning between the two phases is described by a
partition coefficient. This partition coefficient is useful to calculate the concentration of the solute
in both solvents after the extraction. The coefficient mathematical expression is:
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Task 3: Now it’s time for you to perform your last experiment, a liquid-liquid extraction.
Work in pairs. You’ll perform a simple liquid-liquid extraction. Afterwards, you’ll analyze
the concentration of the solutions and you’ll calculate the partition coefficient of the
water-acetic acid-trichloromethane system.
Procedure
Simple liquid-liquid extraction
ATTENTION: Due to the use of CHCl3, all the experiment should be performed in the fume
cupboard. All laboratory technicians should use gloves, coat and security glasses during the
assay.
1. Simple liquid-liquid extraction:
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Check that your separatory funnel and the stopcock at the bottom of the funnel work
correctly. To do so, pour some distilled water inside the funnel and manually shake the
funnel to ensure that no liquid leaks.
Use a graduated cylinder to pour 75 mL of acetic acid 0,1 M inside the funnel.
Add 75 mL of trichloromethane using a graduated cylinder.
Secure the stopper and manually shake the funnel as you have learnt before.
ATTENTION: Remember that the funnel must be shaken pointing away from the body and away
from your lab partners. Keep the funnel inverted and open the stopcock regularly to avoid
overpreassure inside the funnel.
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Place the funnel back in the iron ring and remove the stopper.
Wait until the two phases are completely separated.
Transfer the two layers to different beakers or Erlenmeyer flasks.
Partition coefficient calculation
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To determinate the partition coefficient, analyze the composition of the aqueous phase of
the simple extraction.
Take 25 mL of the aqueous phase in an Erlenmeyer. Add phenolphthalein as indicator.
Titrate the sample with NaOH 0,1 M.
Calculate the concentration of the sample and the partition coefficient.
Task 3 (ALTERNATIVE): In case you want to compare a simple and a multiple liquid to
liquid extraction.
Procedure
Simple liquid-liquid extraction
ATTENTION: Due to the use of CHCl3, all the experiment should be performed in the fume
cupboard. All laboratory technicians should use gloves, coat and security glasses during the
assay.
QUI_01_ Physico-chemical assays of solids. / Unit 3
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1. Simple liquid-liquid extraction:
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Check that your separatory funnel and the stopcock at the bottom of the funnel work
correctly. To do so, pour some distilled water inside the funnel and manually shake the
funnel to ensure that no liquid leaks.
Use a graduated cylinder to pour 50 mL of a 0,45 g/L iodine solution.
Add 50 mL of trichloromethane using a graduated cylinder.
Secure the stopper and manually shake the funnel as you have learnt before.
ATTENTION: Remember that the funnel must be shaken pointing away from the body and away
from your lab partners. Keep the funnel inverted and open the stopcock regularly to avoid
overpreassure inside the funnel.
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Place the funnel back in the iron ring and remove the stopper.
Wait until the two phases are completely separated.
Transfer the two layers to different beakers or Erlenmeyer flasks.
Multiple liquid-liquid extraction
ATTENTION: Due to the use of CHCl3, all the experiment should be performed in the fume
cupboard. You should use gloves, coat and security glasses during the assay.
1. Multiple liquid-liquid extraction:



Check that your separatory funnel and the stopcock at the bottom of the funnel work
correctly. To do so, pour some distilled water inside the funnel and manually shake the
funnel to ensure that no liquid leaks.
Use a graduated cylinder to pour 50 mL of a 0,45 g/L iodine solution.
Add 25 mL of trichloromethane using a graduated cylinder
ATTENTION: Remember that the funnel must be shaken pointing away from the body and away
from your lab partners. Keep the funnel inverted and open the stopcock regularly to avoid
overpreassure inside the funnel.
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

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Place the funnel back in the iron ring and remove the stopper.
Wait until the two phases are completely separated.
Transfer the organic layer to an Erlenmeyer flask, and leave the aqueous layer in the
funnel.
Add 25 mL of fresh trichloromethane and proceed again with the extraction.
Compare the color of the two layers obtained in the simple extraction with the colors of
the layers obtained in the multiple extraction.
Task 4: Work in pairs to write a lab report about the experiment performed in task 3. It’s
time to apply everything you have learnt in this unit. If you have trouble writing your
report, remember to use the language support provided throughout the unit.
When you are done, share your lab report with your teacher through google drive:
Google Drive
QUI_01_ Physico-chemical assays of solids. / Unit 3
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