CHEM 105: CHEMISTRY AND SOCIETY
Sp 05
Lab 2 Solubility - Hypothesis Building
Introduction
In this introductory lab, you will investigate the solubility properties of several substances in
water and in hexane. From a series of observations, you will try to construct a hypothesis
concerning the properties of solute and solvent that determines solubility. In effect, you will be
generating a scientific law. The solutes (the substance dissolved), solvents (the liquid, in the case,
that will dissolve the solute), and their structures are shown in the table on page 2.
Procedure
In the lab you will find small test tubes containing small amounts of sodium chloride, NaCl,
and others containing solid iodine, I2. Take two of each of these tubes. Label the NaCl tubes 1
and the iodine tubes 2. Get 12 more small test tubes and label two of them 3, two of the 4, etc,
through 6. Using the dropper bottles in your hood and a squirt bottle of water, place a small
amount (0.5 ml) of solute 3 (acetic acid) into tubes 3, and the other solutes 4-6 (as described on
the next page) into the other corresponding pairs of tubes. Next place about 0.5 ml of water in
one tube of each pair containing each solute, as described in class. Mix thoroughly as
demonstrated in the lab. Repeat the experiment by adding about 0.5 ml of hexane to the other
tube in each pair. . Note if the solute dissolves in the water and in the hexane. Fill in CHART 1
on the next page. Indicate whether the solute is a solid, liquid, or gas, and use the following
symbols as an indicator of solubility: (s) for soluble, (i) for insoluble, and (ss) for slightly soluble.
The final amount of liquids in Tubes 3-6 should look similar to the picture to the right.
Note: Take special care in observing whether acetic acid (3) is soluble in hexane. As you
mix two liquids, if the liquids are insoluble in each other, you will observe a series of “lines” in the
mixture during the mixing. These lines coalesce into a sharp line which is the boundary between the
two liquid layerss after they have separated from each other. The visibility of the lines and boundary
depends on the index of refraction of the two liquids. If the indices of refraction, which is a
measure of how light bends as it passes through a medium like a liquid, differ greatly for the two
liquids, the boundary line will be very evident, because light, as it passes through the two liquids at
the boundary, will be bent differently. If the indices of refraction don’t differ by much, the boundary
line will be harder to see. If the indices of refraction were the same, you couldn’t see the boundary
at all, even though one liquid would be on top of the other. The boundary is only visible if light
passing through the boundary is refracted differently by the two liquids. The index of refraction of
hexane is 1.3749 and that of acetic acid is 1.37109, so if the two liquids don’t dissolve in eadch
other, you will have to look very hard to see the interface between them. The density of hexane is
0.6548 compared to 1.0492 for acetic acid.
Then, working with your hood partner, devise a hypothesis which will allow you to predict the
solubility properties of solutes in solvents. After you have devised your hypothesis, predict the
solubility of the solutes shown on CHART 2.
Hypothesis: 9 pts
CHART 1: EXPERIMENTAL SOLUBILITY BEHAVIOR: TOTAL OF 6 POINTS
SOLUTE
FORMULA
STATE
STRUCTURAL REPRESENTATION
1. sodium chloride
NaCl
Cl
Na
2. iodine
I2
I
3. acetic acid
I
O
CH3COOH
H3C
4. oleic acid
5. methanol
6. octanol
SOLVENT
OH
C18H35CO
OH
CH3OH
O
OH
H3C
OH
C8H17OH
FORMULA
water
H2O
hexane
C6H12
OH
STRUCTURAL REPRESENTATION
O
H
H
SOLUBILI
TY
IN
WATER
SOLUBILI
TY
IN
HEXANE
CHART 2. Predict the solubility of each of the following solutes in the given solvent, and
record your predictions below: total of 10 pts
SUBSTANCE
STRUCTURE
CaCl2
WATER
Cl
Ca
2
octane
H2C
Triglyceride
(as in vegetable oil)
HC
H2C
O
O
CO(CH 2)14 CH 3
CO(CH 2)14 CH 3
O
CO(CH 2)14 CH 3
CH 3
H3C
O
CH 3
H
vitamin E
3
HO
CH 3
OH
vitamin C
O
O
CH 2OH
H
HO
OH
HEXANE
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MATERIAL SAFETY DATA SHEET
hexane: no hazard in ordinary laboratory use
sodium chloride: irritant;
iodine:
irritant;
acetic acid: acid; corrosive; irritant; avoid contact with skin or eyes; avoid breathing fumes
oleic acid: acid; corrosive; irritant; avoid contact with skin or eyes; avoid breathing fumes
methanol: irritant; flammable; avoid contact with skin or eyes; avoid breathing fumes
octanol: irritant; flammable; avoid contact with skin or eyes
DISPOSAL
Pour contents of all tubes into waste container provided.
PREP NOTES (STAFF ONLY):
1. In each hood, place rack with 12, 10x75 tubes. Label tube two tubes 1, two tubes 2, etc.,
through 6, for a total of 12 tubes.
2. Place a bit of NaCl in tubes 1. Place a few crystals of I2 in tubes 2 and stopper.
3. Place in each hood eye dropper bottle with acetic acid, oleic acid, methanol, and octanol. Each
bottle need only contain 5 ml max.
4. Place in one central hood two Repipet bottles, one containing water and the other containing
hexane.
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