2. One Experimental Summary
Report per lab partners
On of the students in the lab partner pair will
submit the experimental Summary Report.
Remember the Syllabus! One grade for the
lab partner pair (2 people).
Three people in a group ONLY by permission
of the TA.
3. Concept of Solubility
Solubility is the process of a solute (the dissolved substance) being
dissolved into a solvent (the dissolving medium)
Solubility if a very important technique in organic chemistry, and the
concept will be used to some extent in every lab we perform
Structural features of compounds and intramolecular forces are two
components that control if a solute will be able to dissolve in a solvent,
and this lab will help you begin to predict if two things will be soluble with
each other just based on their identity
4. Soluble vs Insoluble (or partially soluble)
We typically describe solubility in terms of something being soluble or insoluble in
a solvent, however this is normally reported quantitatively to determine the extent
of how much of a species will dissolve in a given solvent
Typically this is described in g/L or in mg/mL. Take the following examples of
compounds in water:
Cholesterol: 0.002 mg/mL
Caffeine: 22 mg/mL
Citric Acid: 620 mg/mL
To be considered soluble, you should be able to see a change in the amount of
solid added. Say we added 40 mg of each to 1 mL of water, Cholesterol would be
insoluble, citric acid soluble, and caffeine partially soluble
Cholesterol
Caffeine
Citric Acid
5. Solubility vs Miscibility
A technique similar to solubility is the idea of miscibility,
which we will discuss more in Experiment 4. Miscibility
describes the process of two liquids either mixing together or
staying as separate layers (we’ll be doing this today, but
purely qualitatively).
Both concepts are based on the idea of polarity, however
solubility usually has a broader range, whereas miscibility is
sometimes harder to discern.
In this lab we will be looking at the extent to which two
liquids mix together to determine if they are miscible,
immiscible, or partially miscible.
6. Intramolecular forces
A concept that largely describes solubility is polarity, and the idea of “like species
dissolve like species”
To dive into this topic, we need to look at intramolecular forces
London-Dispersion forces: a weak force in all molecules in which electrons from
neighboring atoms are held together by a nucleus
Dipole-Dipole forces: a stronger force between atoms with high electronegativity
differences, commonly seen in “polar” bonds where electrons are shared unevenly
Hydrogen bonding: a strong force in which hydrogen atoms are electrostatically bound
to a more electronegative atom, typically nitrogen, fluorine, or oxygen
Ionic bonding and covalent bonding: Physical bonding interactions, two atoms bound
together
7. Polarity plays a large role
Organic compounds with hydrogens and carbons are typically considered
nonpolar, as they possess only weak intramolecular forces, whereas compounds
that contain oxygen or nitrogen are usually polar as they are more electronegative
and have stronger forces (hydrogen bonding)
Polarity is a relative term. For example:
Hexane Ethyl Acetate Water
8. Predicting Solubility
Compounds with similar polarities will tend to be soluble together
For example, two hydrocarbon species, hexane and pentane, will be soluble
together as they both only contain carbon-hydrogen bonds
The same can be said for two polar species as well
Hexane Pentane
9. Today’s Experiment
Today we will perform Experiment 2 – Solubility, part B (Solubility of Different
Alcohols)
You will be testing the solubility of three different alcohols in water (a polar
solvent) and hexane (a nonpolar solvent). The alcohols themselves have increasing
carbon chain lengths
Methanol (methyl
alcohol)
1-Butanol 1-Octanol
10. Today’s Experiment
You will need to test each alcohol in both solvents, see table on next slide for all
combinations.
Distilled water is available in each fume hood to use in the squirt bottle
All chemicals can be found in one of the two designated chemical hoods
Dropwise add one of the alcohols to either the water or the hexane, and see if the
two liquids mix. You may see mixing lines that indicate mixing of solutions
If they mix together fully after adding 20 drops they are soluble, if they mix
together slightly at the beginning, but eventually form two layers they may be
partially soluble together, if they do not mix at all when adding, they are insoluble
together
Repeat the procedure for the other combinations. See table on the next slide for
all the required combinations.
11. SUMMARY OF EXPERIMENTAL PROCEDURE AND POSSIBLE OUTCOME-a larger
version of this table is available to you in D2L, you will need it.
NOTE: Observations will involve more than just the words “soluble”, “miscible” or any other single
word for an observation. Single word observations will be given a grade of zero.
TEST OBSERVATION INFERENCE/MISCIBILITY
Water + 20 drops Methanol
Water +20 drops 1-butanol
Water + 20 drops 1-octanol
Water + 20 drops hexane
Water + 20 drops unknown
TEST OBSERVATION INFERENCE/MISCIBILITY
Hexane + 20 drops Methanol
Hexane + 20 drops 1-Butanol
Hexane + 20 drops 1-octanol
12. SAFETY
These alcohols (and hexane) are flammable, and can be skin irritants. Wear gloves
and avoid coming into skin contact with them when using them.
Additionally, avoid getting into your eyes (that’s why we wear goggles!)
If in contact, wash with water to thoroughly remove liquid.
Avoid breathing in the vapors, as they can be noxious.
If you break any glass or spill anything, notify the TA right away so they may clean
it up.
13. Experimental observations
For your groups’ report you will need to have a table similar to the one shown
previously (slide 11). You may fill out the table on the previous slide. Save it, then
upload it into the D2L report.
• Fill in the table by saying if the alcohol is miscible, immiscible, or partially
miscible with the respective solvent (water or hexane)
• You will also need to write down your observations to explain the reasoning
behind your choice
• Additionally, you will need a section for your unknown of choice
14. Looking Forward
The next lab will be Melting Point and Crystallization.
Be sure to complete your Experimental Preparative Knowledge BEFORE coming to
lab the week of September 19th. This is located in the quizzes section of D2L.
Only students who complete the experimental preparative knowledge BEFORE lab
will be allowed to complete the melting point and crystallization experiment the
week of September 19th.
