Name____________________________________________________ Date________________ Period_______
Chemistry 11
Ionic vs. Molecular Compounds Lab
Introduction
A compound is defined as a chemical combination of two or more elements. A chemical bond is the “glue” holding
together atoms of different elements. Two types of bonds are ionic and covalent.
Ionic bonds generally occur between a metallic atom and a nonmetallic atom. The bond results from the transfer of one or
more electrons from the metallic atom to the nonmetallic atom, resulting in a charge difference. The positively charged
metal ion is then attracted to the negatively charged non-metallic ion.
Covalent bonding generally occurs between two or more nonmetallic atoms. Covalent bonding involves the sharing of
electrons.
Properties such as melting point, boiling point, solubility, electrical conductivity, color, and odor can help you distinguish
ionic from covalent compounds (as we saw in Table 5.1 on page 160). As in many areas of chemistry, the distinctions are
not always clear, nor do the distinctions apply to all compounds.
The salt and sugar on your kitchen table both dissolve easily in water, but the solutions they form have an important
difference. One of those kinds of white crystals is an ionic compound, and when it dissolves, it dissociates, or breaks up
into ions. The ions are free to move in the solution, and that solution, therefore, conducts electricity. The more ions in
solution, the better it conducts electricity. If something produces a large amount of ions it is called a strong electrolyte. If
something produces a small amount of ions, it is called a weak electrolyte. The other kind of crystal, however, is a
molecular compound, and its molecules remain whole when they dissolve. With no ions, that solution does not conduct
electricity. If something produces no ions, it is called a nonelectrolyte.
In this experiment, you will observe several properties of some ionic and some covalent compounds and attempt to
recognize patterns among the properties. You will then use those generalizations to identify the compounds as either ionic
or molecular. The patterns you may recognize are generalizations and may not necessarily apply to all ionic and covalent
compounds.
Pre-lab Assignment
Read the Introduction and Procedure before answer the following questions. This must be completed before doing the
lab.
1. What kinds of elements generally form ionic compounds?
metals and non metals_______________________________
2. What kinds of elements generally form covalent compounds? __2 or more non metals_________________________
3. How do aqueous solutions of ionic and molecular compounds differ?
ionic compounds produce ions and can therefore conduct electricity; molecular
might dissolve but don’t produce ions (they stay intact) and therefore don’t
produce electricity
4. When some ionic compounds dissolve, not all of their bonds dissociate. What kind of conductivity
would you expect such a solution to have?
slight conductivity: the light bulb would glow, but not as brightly as it does in a solution
like sodium chloride.
5. Based on the formula, predict whether each of the following compounds is primarily ionic or
primarily covalent.
A. sodium iodide NaI _______ionic___________
B. methane CH4 ______covalent/molecular____________
C. calcium chloride CaCl2 ____
D. ammonia NH3 ____
covalent/molecular ___________
E. glucose C6H12O6 _____
Page 1 of 5
ionic _______________
covalent/molecular ________
Name____________________________________________________ Date________________ Period_______
6. Explain the reason why you will test solubility with both hexane and water.
______________________________________________________________________________________________
_________so that we can get a sense of whether the compounds are polar (ionic) or non polar
7. In your own words, write the purpose of this experiment. ____
learn ionic and covalent and to determine which compounds are ionic and which are
molecular
Purpose
To observe several properties of some ionic and some covalent compounds and attempt to recognize patterns among the
properties as well as to identify the compounds as either ionic or molecular.
Equipment
aluminum foil
burner
6 test tubes
large iron ring
ring stand
scoopula
conductivity apparatus (Mrs. Doyle will take care of this)
glass lens
Materials
sucrose
calcium chloride
sodium chloride
citric acid
water
paraffin wax
benzoic acid
hexane
Procedure
Relative Melting Point Determination
You will not measure the exact values for the melting point. The order in which the compounds melt will give relative
melting points.
Use hot plate
Page 2 of 5
Name____________________________________________________ Date________________ Period_______
Solubility in Water
The phrase “like dissolves like” means that compounds will dissolve other compounds with similar bond types. Water, a
polar molecule, will dissolve both ionic compounds and molecular compounds with polar molecules.
5. Put a few crystals of each of the compounds in separate test tubes. Make sure you know the order of the compounds.
Don’t forget to add your compound too!
6. Add water until each test tube is about half full. Gently shake each test tube. It is necessary to observe the solids for
several minutes to determine if they dissolve or not.
Place a check in your data table by the substances that are able to dissolve.
7. Empty the test tubes appropriately and rinse them out. What must go in a “waste” beaker? What can go down the
drain? Please ask if you aren’t sure.
Solubility in Hexane (Do this in the fume hood) Mrs. Doyle will do this with the compounds.
The phrase “like dissolves like” means that compounds will dissolve other compounds with similar bond types. Hexane is
a non polar solvent which means that it’ll dissolve molecular compounds that contain non polar bonds.
8. Put a few crystals of each of the compounds in separate test tubes (Don’t forget to add your compound too!). Make
sure you know the order of the compounds.
9. Add only enough hexane to cover your sample. Gently shake each test tube. It is necessary to observe the solids for
several minutes to determine if they dissolve or not. Place a check in your data table by the substances that are able to
dissolve.
10. Empty the test tubes appropriately and rinse them out. What must go in a “waste” beaker? What can go down the
drain? Please ask if you aren’t sure.
Conductivity of Aqueous Solution
If an aqueous solution contains ions, then it will conduct electricity, completing the circuit and lighting up the bulb. A
strong electrolyte will light the bulb brightly; a weak electrolyte will light the bulb dimly. A solution containing nonpolar
molecules will not conduct electricity.
11. Using the conductivity apparatus and aqueous solutions already set up, test the conductivity of each solution by
dipping both electrodes into the beaker. Mrs. Doyle will be sure to rinse the electrodes with the water between
solutions. Record in Data Table if the light bulb does not light up, lights up dimly, or lights up brightly.
12. Arrangements can be made to test the conductivity of your compound too!
Disposal and Cleanup
Excess compounds can be rinsed down sink. Clean the test tubes well and put them away. Aluminum foil may be thrown
away.
Page 3 of 5
Name____________________________________________________ Date________________ Period_______
Data Table
Compound
Formula
Phase
at
room
temp.
(s, l or
g)
Relative
Melting
Point
(“1” means
first to
melt)
Solubility
in water
Solubility
in Hexane
Colour of
Aqueous
Solution
(* see note
below)
Solution
Conductivity
Calcium
chloride
CaCl2
S
2
31 s
Yes
No
Colourless &
cloudy
Yes
Dimmer than
NaCl
Citric acid
Benzoic acid
C6H5COOH
S
3
1min03s
No
No
N/A
No
Paraffin Wax
C25H52
S
1
26 s
No
Yes
N/A
No
Sodium
Chloride
NaCl
S
5
Didn’t melt
Yes
No
Colourless &
cloudy
Yes
bright
Sucrose
C6H12O6
S
4
5 mins
Yes
No
Colourless
No
*This is only applicable for compounds that dissolve in water. Remember that “clear” is not a colour; use the word
“colourless”
Analysis
You may put your answers in the spaces provided or on a separate sheet of paper.
1. Group the compounds into two groups according to their properties. List the properties of
each group. Include melting point (high or low), conductivity of an aqueous solution, and
solubility in water, solubility in hexane.
______________________________________________________________________________________________
______________________________________________________________________________________________
______________________________________________________________________________________________
______________________________________________________________________________________________
______________________________________________________________________________________________
______________________________________________________________________________________________
2. Do all of the members of the group exhibit all of the same properties? Give specific examples from this experiment.
______________________________________________________________________________________________
______________________________________________________________________________________________
______________________________________________________________________________________________
______________________________________________________________________________________________
Page 4 of 5
Name____________________________________________________ Date________________ Period_______
Conclusions
Determine which of the groups consists of ionic compounds and which consists
of molecular compounds.
Write a short paragraph to summarize the properties of ionic compounds. Write
another short paragraph to
summarize the properties of molecular compounds. Include 1) physical state at
room temperature,
2) melting point, 3) conductivity of aqueous solution, and 4) solubility in water
5) solubility in hexane
1.
See and be comfortable with Table 5.1: Comparing Ionic and Molecular
Compounds
2. Properties of compounds depend on the strength of the attractive forces between
particles. The particles that
compose an ionic compound (ions) are held together by ionic bonds. The
particles that compose a molecular
compound (molecules) are held together by intermolecular forces.
Which are stronger bonds, ionic bonds or intermolecular forces? Which have
higher melting points, ionic
compounds or molecular compounds?
Ionic bonds are stronger than intermolecular bonds. Ionic bonds have higher
melting points. This is due to the strong bond between the anions and cations
(electrostatic attraction) – because of the strength of these bonds they require a
lot of energy to be broken.
3. How can you account for the fair, poor, and non-conductors of electricity
through the explanation of bond types?
Electricity requires “free” ions in order to be conducted.
Ionic compounds may be fair or poor conductors of electricity depending on how
many ions are present in the solution.
Molecular compounds do not conduct electricity because their bonding does not
lend itself to the formation of ions.
Page 5 of 5