Chemistry 32A
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Cover sheet for
Polar & Non-Polar Materials
Student name (please print)
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Lab section, day and time
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Date report submitted
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Provide your assessment of the experiment, some suggestions:
What did you learn from the experiment? Please be specific
Were instructions clear and/or easy to follow, sufficient time for completion?
Highlights and/or lowlights? Suggestions for improvement?
Use the space below, or attach comments on a separate sheet
POLAR AND NON-POLAR MATERIALS
Solubility of one material (solute) in another (solvent) depends on compatibility of molecular structure
between the two, often summarized by “like dissolves like”. Materials with no electrical polarity are
referred to as “nonpolar”, examples of which include atmospheric gases, oils, and many organic
solvents. Other materials have molecular polarity, meaning a charge separation resulting in either
charged particles as ions or asymmetric molecules having a positive and negative end, similar to the
north and south poles of a bar magnet.
The separation of charge is due to an element’s electro negativity, with Fluorine being the most
negative, meaning it has the strongest ability to attract electrons. This unequal electron attraction
results in ions or molecules with positive and negative ends. These are “Polar” and have the property
of mixing with other polar materials, leading to the generalization that “like dissolves like”.
Water is the most common polar material and dissolves most other polar materials, such as salt and
sugar. Materials which do not have a separation of charge, or have charges which are evenly balanced
are considered “nonpolar”.
Polarity is symbolized by the small Greek letter delta (δ) with a plus or minus sign added to indicate
charge. The charge direction can also be indicated with an arrow, which head faces the negative end of
the molecule and the other end has a cross indicating the positive end.
In the process of dissolving in water, polar materials often generate ions, which are charged molecular
species surrounded by water molecules, illustrated below. This ionic solution can conduct an electric
current similar to electrons in a wire.
\
Some materials are “in between”, being polar (dissolve in water) but do not conduct an electric
current. These are called Polar Covalent, an example of which is Sucrose ... ordinary table sugar.
Solubility also depends on temperature. Our everyday experience is that things dissolve more quickly
or completely in hot rather than cold water, so we wash dishes and clothes using hot water to
accelerate the cleaning action.
For gases, the reverse is true. Oxygen and Carbon Dioxide are more soluble in cold water.
PROCEDURES
Part A: Solubility in Polar (water) and Non-Polar (hexane) solvents
You will evaluate the solubility of 12 solutes in two solvents, for a total of 24 samples. In the case of
water you will also do a conductivity test using an LED indicator attached to a battery. If the light
glows, it indicates conductivity.
1. Label 12 test tubes with the solute to be tested; then fill about 1/3 with distilled or deionized
water after making sure they are clean and rinsed with deionized water. You must NOT use tap
water which has enough dissolved salts to be electrically conductive without added solutes. Do
the same with 12 more test tubes and fill about 1/3 with hexane.
2. Add a small amount of each solute to the respective labeled test tubes containing water or
hexane. An amount the size of a few grains of rice is sufficient. Swirl or tap the test tubes and
observe if the solute is dissolving. Solutes should dissolve in one solvent but not the other. In
some cases a strong color will confirm dissolving. For vitamin E, it will be necessary to cut the
end off a capsule and squeeze a drop of oil into the test tubes.
3. Decide which materials are soluble in which solvents and enter the data on your lab manual
data sheet.
4. For solutes in water, use the conductivity probe to see if the solution is electrically conductive
or not. Relative conductivity is shown by brightness of the LED, and is an indication of
ionization.
5. Decide whether each solute is polar, nonpolar, or polar covalent
solute is soluble in water?
Yes
conducts electric current ?
( light is ON )
Yes
Polar
Ionic
No
Polar
Covalent
No
Soluble in Hexane?
Yes
non-Polar
Covalent
No
insoluble
Part B: Effects of temperature on solubility of a gas
Carbon dioxide is soluble in water, commonly found in soft drinks, seltzer water, beer, champagne,
and the like. The gas forms a weak acid which gives these drinks a pleasant acidic taste, but the
beverage “goes flat” after sitting in an unsealed container overnight. You will investigate the escape of
gas which turns the acidic solution neutral. The reversible reaction:
H2O + CO2 → H2CO3 → H+ + HCO3- → H2O + CO2↑
CO2 & water
under pressure
acidity via hydrogen ion
CO2 evaporation
1. Fill one 150 or 250 mL beaker about 1/3 full with carbonated water (Perrier, seltzer, or
equivalent).
2. Fill another with distilled water to the same level. Add enough bromphenol blue indicator to
both to get a distinct color.
3. Place both beakers on a hot plate for about 10 minutes, or long enough to see a color change.
Note the result in your lab report.
Part C: Effects of temperature on solubility of a solid
Most solids dissolve better and faster in hot versus cold water. You will observe this by adding a
highly colored solute to cold and hot water to see the difference.
1. Place a large test tube 1/2 full of water in a beaker of hot water on a hot plate, and leave it to
heat for about 5 minutes. Note temperature of the hot water bath
2. Place another large test tube 1/2 full of water in an ice-bath beaker and leave for about 5
minutes to cool to the ice temperature. Note temperature of the ice water bath
3. While one student holds the hot and cold water test tubes, a lab partner will drop equal
amounts of Potassium Permanganate (about the size of a rice grain) into each tube
simultaneously; and both will observe the speed and depth of color indicating degree of
dissolution over time. Suggested observations at 10 seconds, 1 minute, and 5 minutes. Place
the test tubes in a rack or beaker for 15 minutes and observe at room temperature. Is there any
diffeence?
DATA SHEETS
SOLUBILITY & CONDUCTIVITY, Data Page 1
You MUST use DISTILLED WATER in theis experiment, tap water is conductive by itself.
Samples of 12 materials in test tubes with water … which ones dissolved? (yes or no)
Insert conductivity probe in water+solute test tubes, note LED brightness, or no light at all
Repeat with samples of 11 materials in Hexane, which ones dissolved (yes or no)
1 Sucrose (table sugar)
2 Iodine
4 Calcium Chloride
CaCl2
5 Sodium Chloride
NaCl
6 Potassium Permanganate
KMnO4
7 Cholesterol
C27H46O
8 Ascorbic Acid (vitamin C)
C6H8O6
9 Octanol
C8H17OH
12 Hexane
Solubility in
Water (polar)
Brightness
Hexane (nonpolar)
I2
NH4Cl
11 Vitamin E
LED
C12H22O11
3 Ammonium Chloride
10 Vegetable Oil
Solubility in
triglyceride
α-Tocopherol
C6H14
xxx (same thing)
Notes to Conductivity Testing
LED intensity indicates degree of ionic conductivity, bright light (≈20ma) means good conductor
Dim light indicates reduction in electrical conductivity, fewer ions available, but still ionic.
NO light indicates material is NON-conductive and NON-ionic
Touching the leads together is useful to verify opertion and establish relative brightness
OBSERVATIONS, data page 2
Part B: Temperature Effect on the Solubility of Gases
Describe any color changes observed in the soda water plus indicator "Bromthymol Blue"after heating
for about 20 minutes. Carbontion mkes the water acidic
Solution color at room temperature (carbonated)
Solution color after heating (no carbonation)
Part C: Temperature Effect on the Solubility of Solids
Place a test tube half full of distilled water in beaker of ice water for about 5 minutes, and do the same
thing with a test tube immersed in hot water. Record the temperature in each beaker. Place several
grains of Potassium Permnganate on tips of two wooden stir sticks. While one student holds the hot and
cold water test tubes the lab partner will drop the permanganate in both test tubes at the same time.
Observe the color difference for a few minutes, and place the test tubes aside (in a rack or beaker) until
they come to room temperature (about 15 minutes). Observe the following, and describe intensity of
color seen. Describe observations such as "light, dark, darker, darkest ... etc.)
Cold Water test tube
Hot Water test tube
Temperature reading, oC
The first few seconds
after 30 seconds
after 1 minute
after sitting for 15 minutes.
Summarize your observations on speed of solution versus temperature
POST LAB QUESTIONS, data page 3
1
Based on YOUR solubility and conductivity results, describe differenced between Polar & non polar
compounds in your own words.
2
For the 12 solutes you tested, classify each as ionic & polar, covalent & polar, or covalent & non polar. Note
that if the material dissolved in water it must be polar, and if conducts an electric current it must be ionic as
well. If a material dissolves in water but does NOT conduct an electric current, it must be polar-covalent ...
only one of those in this experiment.
ONLY ONE "YES"ANSWER PER ROW REQUIRED
Solubility Criteria :
Electrical Conductivity Criteria:
1
Sucrose
C12H22O11
2
Iodine
I2
3
Ammonium Chloride
NH4Cl
4
Calcium Chloride
CaCl2
5
Sodium Chloride
NaCl
6
Potassium Permanganate KMnO4
7
Cholesterol
8
Ascorbic Acid (vitamin C) C6H8O6
9
Octanol
10
Vegetable Oil
11
Vitamin E
12
Hexane (a solvent)
C27H46O
C8H17OH
triglyceride
α-Tocopherol
C6H14
IONIC
Covalent
COVALENT
Polar
water soluble
conductive
Polar
water soluble
non-conductive
non-polar
oil soluble
non-conductive
POST LAB QUESTIONS data page 4
3a
What property do covalent solutes have in common regarding conductivity in water?
3b
Did all covalent compounds we evaluated dissolve in Hexane?
4
Vitamins are classified as water soluble or fat soluble
How would you classify the two vitamins you tested in terms of POLARITY of the solute?
4a Vitamin C
4b Vitamin A
5
Acetic acid (vinegar) is a covalent compound, but when dissolved in water, it is a weak electrolyte.
How would you explain this result?
6
What change of the indicator in carbonated water did you observe after heating?
6a Describe color change
6b Eaplain the result: