Arnoldi / Lazaar
Chem Com
Unit One Part C
Solvents: The Likes Dissolve Likes Laboratory
What do the terms “soluble” and “insoluble” mean? Is anything truly insoluble in
water? In most cases of ionic compounds in water, at least a very few ions always dissolve,
therefore the term “insoluble” refers to ionic substances that are only very slightly soluble
in water. While this is true for ionic substances in water, for most solutes dissolving in
most solvents, it is easiest to predict solubility based upon the type of bonding that is
occurring, the distribution of the bonds in the molecule, and the concept of “Likes
Dissolve Likes”.
Ionic solutes, for example, have one section of the formula unit that is completely
positive and completely negative. Therefore, they look to dissolve in solvents that have
charged sections as well. Because there are no ionic solvents, which have completely charge
sections, they look to dissolve in polar solvents which have partially negative and partially
positive sections. In this way, (charges / partial charges), they are alike.
Covalently bonded solutes, on the other hand, can result in two different types of
molecules. Polar molecules exist if the electrons are unevenly distributed in the molecule.
These polar molecules have partially positive and partially negative sections in the molecule.
Therefore, polar molecules look to dissolve in solvents that have partially negative and
partially positive sections in their molecules. In this way, they are alike (partial charges /
partial charges). In other words, polar solutes dissolve in polar solvents.
The other type of covalently bonded solutes are those in which electrons are evenly
distributed throughout the molecule. These nonpolar molecules do not have any charged
portions in their molecules. Therefore, nonpolar molecules look to dissolve in solvents that
do not have charged sections in their molecules. In this way, they are alike (no charges / no
charges). In other words, nonpolar solutes dissolve in nonpolar solvents.
In this activity, you will have the opportunity to observe the concept of “Likes
Dissolve Likes”. You will see that substances dissolve in one another based upon their polar
or nonpolar nature. If the solute dissolves in the solvent, it is said to be soluble. If the
solute does not dissolve in the solvent, it is said to be insoluble. You will attempt to dissolve
several solutes into both a polar solvent and a nonpolar solvent. You will also have the
opportunity to hypothesize about the polar nature of two unknowns, based upon the solvent
that dissolves each substance.
MATERIALS
Test Tubes (5)
Test Tube Rack
Test Tube Brush
Unknown Solutes
A
B
Solvents:
Distilled Water (polar)
Mineral Oil (nonpolar)
Known Solutes
POLAR: Acetic Acid, Ethanol, sugar
IONIC: Iron (III) Nitrate
NONPOLAR: Cooking Oil
PROCEDURE
PARTNER A: Testing the Knowns in Distilled Water
1. Fill five test tubes with three pipets of distilled water.
2. Add one pipet of acetic acid to the first test tube, one pipet of ethanol
to the second test tube, one pipet of cooking oil to the third test tube, a
few crystals of Iron (III) Nitrate to the fourth test tube, and a few
crystals of sugar to the fifth test tube.
3. Gently swirl each test tube.
4. KEEP YOUR TEST TUBES SET-UP!
PARTNER B: Testing the Knowns in Mineral Oil
1. Fill five test tubes with three pipets of mineral oil.
2. Add one pipet of acetic acid to the first test tube, one pipet of ethanol
to the second test tube, one pipet of cooking oil to the third test tube, a
few crystals of Iron (III) Nitrate to the fourth test tube, and a few
crystals of sugar to the fifth test tube.
3. Gently swirl each test tube.
4. KEEP YOUR TEST TUBES SET-UP!
PARTNER C: Testing the Unknowns
1. Fill two test tubes with three pipets of distilled water.
2. Fill two test tubes with mineral oil.
3. Add one pipet of unknown A to the first and third test tubes, and one
pipet of unknown B to the second and fourth test tubes.
4. Gently swirl each test tube. Record if the solute dissolved (mixed with
the solvent), or did not dissolve (can still be seen as a separate entity from
the solvent).
5. KEEP YOUR TEST TUBES SET-UP!
PARTNERS A, B, and C together:
Comparing Data
1. Bring all of your test tube racks together. Be sure to know which is
which! Now, compare results.
2. Each solute will either dissolve in the mineral oil or the water. (Never
both, never neither).
3. Record results in the table below.
DATA
Record Observations as: Dissolved or Did not Dissolve
Solute Tested
Mineral Oil as the Solvent
Water as the Solvent
Acetic Acid
Ethanol
Cooking Oil
Iron (III) Nitrate
Sugar
Unknown One
Unknown Two
4. Clean all test tubes with soap, water and a test tube brush. Return
equipment to its original position.
Arnoldi / Lazaar
ChemCom
Unit One Part C
Covalent Properties Laboratory Write-up
DATA
1. Fill in the blanks below based upon your laboratory results.
Acetic Acid dissolved in
__________________.
Ethanol dissolved in
__________________.
Cooking Oil dissolved in
__________________.
Iron (III) Nitrate dissolved in
__________________.
Sugar dissolved in
__________________.
Unknown One dissolved in
__________________.
Unknown Two dissolved in
__________________.
2. Based on your knowledge from class notes, answer the following questions:
(Remember, polar molecules have slightly positive and slightly negative ends).
Which solvent, water or mineral oil, is polar?
________________
Which solvent, water or mineral oil, is nonpolar?
________________
ANALYSIS
1. CIRCLE the correct answer.
Generally speaking, in what type of solvents do polar solutes dissolve?
Ionic
Polar Covalent
Nonpolar Covalent
Any
Generally speaking, in what type of solvents do nonpolar solutes dissolve?
Ionic
Polar Covalent
Nonpolar Covalent
2. Error Analysis
CONCLUSION
1. Was unknown A polar or nonpolar? How do you know?
2. Was unknown B polar or nonpolar? How do you know?
Any