EXPERIMENT - 6
Solubility and Conductivity
INTRODUCTION- One of the important physical properties of a chemical compound is its solubility.
When a compound is soluble in another, the two form a solution. A solution is a homogeneous mixture
that generally contains a large amount of one component (solvent) into which a small amount of another
component (solute) is dissolved.
You probably have observed that some pairs of liquids, such as oil and water do not mix (immiscible
liquids), whereas others, such as alcohol and water do mix readily (miscible liquids). Two compounds
that do dissolve in one another are said to be soluble and form a solution as described above. Those that
do not dissolve are referred to as insoluble. The common description used to describe this phenomenon
is “like dissolves like”.
“Like dissolves like” is a general rule frequently stated by chemist. This rule means that the more similar
substances are in their properties, then the more likely the substances are to dissolve in one another. Polar
compounds are more soluble in polar solvents and less soluble in nonpolar solvents; and nonpolar
compounds are more soluble in nonpolar solvents and less soluble in polar solvents. A molecule like
water, which has an angular shape (bent) the bonds form an angle of 105o and which has polar H-O
bonds, has a partial positive charge at the hydrogen end and a partial negative charge at the oxygen end.
Water has two poles (dipole); it is a polar molecule. The polar nature of the water molecule is largely
responsible for its ability to dissolve ionic compounds and other polar covalent compounds. Many
chemical reactions and most biochemical reactions take place in water.
On the other hand, molecules such as cyclohexane (C6H12), carbon tetrachloride (CCl4), and
dichloromethane (CH2Cl2), which have polar C-H, C-Cl, and C-C bonds but a symmetrical distribution of
the bond are not dipole molecules. They are nonpolar molecules. Kerosene, oil, and gasoline are also
nonpolar compounds.
Soluble ionic compounds contain positive and negative ions that are attracted to polar compounds like
water but not to nonpolar compounds. If ionic compounds dissolve in water, the charged ions are free to
move about in the solution independent of each other. These solutions will conduct an electric current. An
electric current is the movement of charged particles, which are electrons in a solid such as metal or
charged ion in a solution.
Aqueous solutions of some substances will conduct electricity. These solutions are called electrolytes.
Other substances whose solutions will not conduct an electric current are called nonelectrolytes.
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When an electrolyte is dissolved in water, ions are produced. Ions are responsible for conductivity. We
will distinguish between two types of substances that produce ions in solution. Strong electrolytes form
aqueous solutions that conduct electricity very easily. The conductivity is high because strong electrolytes
in solution exist almost entirely as ions. Weak electrolytes, on the other hand, form solutions that are
poorer conductors. In solution, weak electrolytes exist primarily as molecular substances with only a few
ions. Electrolytes may be ionic solids such as sodium chloride, NaCl, or they may be covalent compounds
that react with the solvent to produce ions in solution.
Ionic:
NaCl (aq)  Na+ (aq) + Cl+ (aq)
Covalent:
HCl (g) + H2O (l)  H3O + or H +(aq) + Cl- (aq)
If both ions in an ionic compound are charged (more positive or more negative) and small in radius
(ionic size), these compounds tend to be less soluble. Review solubility rules for solubility of compounds
in water.
Electrolytes are vital constituents of body fluids. Hydrochloric acid secreted in the stomach aids in
digestion. Solutions, which bathe cell walls, need to be in proper electrolytic balance to control the
passage of fluids through the walls. Nerve impulses depend on ions to provide electrical conductivity.
We can easily test all solutions for their conductivity by placing them in an electrical circuit in such a way
so that a light bulb glows brightly for strong electrolytes, dimly for weak electrolytes, and does not glow
at all for nonelectrolytes.
Strong electrolytes (SE)
sodium chloride, NaCl
potassium acetate, KC2H3O2
nitric acid, HNO3
sodium hydroxide, NaOH
sulfuric acid, H2SO4
Weak electrolytes (WE)
acetic acid, HC2H3O2
carbonic acid, H2CO3
ammonium hydroxide, NH4OH
(ammonia)
sulfurous acid, H2SO3
Nonelectrolytes (NE)
ethanol, C2H5OH
methanol, CH3OH
acetone, CH3OCH3
glycerin, C3H5 (OH)3
ethylene glycol ,C2H4(OH)2
(antifreeze)
In this experiment you will test the solubility of several compounds in water and cyclohexane. From the
solubility properties, you will predict whether the compound is like water (polar) or like cyclohexane
(nonpolar). The solubilities of many substances, not gases, increase with increasing temperature. An
increase in pressure increases the solubility of gases but affects solid and liquid solubilities very little.
In addition to being soluble in water, you will test such solutions for their conductivities using a
conductivity tester, light emitting diode (LED), to indicate the electrical current from produced ions.
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Experimental Procedure
Part I – Solubility
Select ten test tubes (smallest test tubes) and add a small amount of substance in each, (for solids use a
sample less than the size of a match head and for liquids use a few drops). Add about 1 ml (15-20 drops)
of distilled water (or tap water) to each of the ten test tubes. Shake each test tube well and test each
substance one at a time for water solubility. Record your observations on the report form as soluble (S),
insoluble (INS), or slightly soluble(SS).
Part II – Conductivity
CATION- The bare electrodes are a hazard! DO NOT TOUCH the electrodes when the apparatus is
plugged in. Your skin will conduct an electric current and cause a SHOCK.
Select one solution at a time to test. Place the electrodes (diode) in the solution and observe the light bulb.
Identify the solution as strong electrolyte (SE), weak electrolyte (WE), or a nonelectrolyte (NE).
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EXPERIMENT – 6
REPORT FORM
Name ___________________________
Instructor ________________________
Date ______________
Part I – Solubility
Substances
Solubility in water
1. sucrose
2. ammonium chloride
3. naphthalene
4. sand (silicon dioxide)
5. sodium chloride
6. vegetable oil
7. mineral oil
8. toluene
9. potassium permanganate
10. ethyl alcohol
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Solubility in cyclohexane
Part II – Conductivity
aqueous solutions
formula
physical states
1. tap water
2. sodium chloride
3. sodium hydroxide
4. potassium nitrate
5. acetic acid (vinegar)
6. rubbing alcohol
(isopropanol)
7. hydrochloric acid
8. ammonium hydroxide
9. sugar (sucrose)
solution
10. acetic acid +
sodium chloride
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color
ionic/covalent
EXPERIMENT – 6
Name
Pre- laboratory Questions and Exercises
Due before lab begins. Answer in space provided.
1. Define the following terms:
a. conductivity
b. solubility
2. Define strong electrolyte, weak electrolyte, and nonelctrolyte and give one example of each.
3. Give two special safety precautions that must be observed during this experiment.
4. What are the consequences of students in a chemistry lab disposing of organic solvents such as
toluene, cyclohexane, and oil in the sink?
5. Arrange the following list of solutions from poorest to best conductors of electricity:
hydrochloric acid
ammonium hydroxide
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water
toluene
EXPERIMENT – 6
Name
Post- laboratory Questions and Exercises
Due after completing lab. Answer in space provided.
1. Define the following terms:
a. polar substance
b. nonpolar substance
2. Define miscible and immiscible liquids and give one example of each.
3. Write an equation for the solution of the following in water:
a. H2SO4
b. Ca(OH)2
c. sodium acetate, NaC2H3O2
4. What are the factors (at least four) which increase solubility of a solute in a solvent?
5. Predict whether the following compounds are ionic, polar covalent, or nonpolar.
a. Na2SO4 _______
e. Acetone, CH3 CO CH3 ________
b. Octane, C8H18 _______
f. Ether ________
c. NaC2H3O2 _______
g. Gasoline ________
d. Methanol, CH3OH _______
h. Carbon tetrachloride ________
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