Ionic and Covalent Compounds Tests
Purpose:
Use physical properties to distinguish between ionic and molecular compounds.
Introduction:
Chemical compounds are combinations of atoms held together by chemical bonds. These
chemical bonds are of two basic types- ionic and covalent. Ionic bonds result when one or more
electrons are transferred from one atom to another and ions are formed. Covalent bonds are formed
when atoms share electrons.
Physical properties of a substance such as melting point, conductivity (the ability to carry an
electric current), and solubility can tell us a lot about the type of bond in a compound. Since ionic
bonds involve the creation of ions (atoms with electrical charge), they tend to conduct electricity
when dissolved in water. Since the substance is made of ions, there is a lot of attraction between
particles in the compound in the solid phase, raising their melting point. In this experiment, you will
conduct tests on various compounds, then classify each group as ionic or covalent based on the
physical properties you tested.
Question for this Lab: What properties are exhibited by ionic compounds and covalent compounds?
Null Hypothesis:
Compounds Tested in This Lab:
Copper (II) Sulfate
Sucrose (C12H22O11)
Dextrin (C6H10O5)
Citric Acid
Calcium chloride
Sodium chloride
Procedures:
Safety:
1) Some of these compounds are poisonous. Goggles must be worn at all times to protect
your eyes.
2) If you spill chemicals on your skin, rinse them off.
3) You will be working with fire. Fire is hot. It will burn you! Be careful around your Bunsen
Burner. Anyone playing around in lab will immediately be given a zero for the lab!
4) If you break or spill something or have some type of catastrophe, tell your teacher
immediately!
Relative Melting Point Determination:
1) Obtain a small sample of each compound (no more than the tip of a scoopula) in separate wells in
a well plate. Record a brief description of each substance in your data table.
2) Cover a large iron ring with a single layer of aluminum foil. Using your finger or tip of an eraser,
gently put small divots in the aluminum foil. This will serve as the place where you
will put your chemicals. You want the divots spread out far enough from each other that chemicals
will not run into each other when they are heated. You will also want to make your divots deep
enough.
3) Place the iron ring on the ring stand. Adjust the height of the ring so that once the burner is lit
and placed under the foil, the flame does not touch the foil.
4) Place a FEW crystals of each of your compounds in separate divots in the aluminum foil. Do not
allow the samples of crystals to touch!
5) Place the Bunsen Burner to the side of the ring stand. Light the Bunsen Burner and make
adjustments to the burner until you get a blue flame where the very tip of the flame is
yellow/orange. We do not want to see the double blue flame cone shape. This is too hot!!! If you
are not sure you have the correct flame, ask your teacher to check your flame before you start the
experiment! Make sure the flame does not touch the foil! You should be melting the compounds and
not burning them.
6) Record the order of the samples melting in your data table (1st, 2nd, 3rd, etc). After 10 minutes,
record which compounds did not melt in your data table.
7) Extinguish the burner. Make sure your gas is cut off. Allow the foil to cool while you complete
the remainder of the experiment.
Solubility in Water:
1) Put a few crystals of each of the white solids in the wells of your well plate. Make sure you know
the order of the compounds or the number of the well plate.
2) Add 10 drops of distilled water to each of the six compounds. Stir using a plastic toothpick. It is
necessary to observe the solids for several minutes to determine if they are soluble or insoluble.
Record this in your data table.
Conductivity of Aqueous Solutions:
1) Using the conductivity apparatus and aqueous solutions already present from your solubility test
in the procedures above, test the conductivity of each compound by dipping both electrodes into the
well plate. Record in the data table if the light bulb does not light up, lights up dimly, or lights up
brightly.
2) Be sure to rinse the electrodes with distilled water and wipe them thoroughly between tests.
Also, do not touch the electrodes to the sides of bottom of the plastic well plate.
Disposal and Clean Up:
1) Any remaining solids must be placed in the trash can. Solids are never rinsed down the sink!
Clean the well plate by rinsing it in water.
2) Used aluminum foil may be thrown away.
Data Table:
Be sure to make a thorough, specific title for the data table before putting it in your lab book. For
the compounds in the table without a formula, you must write the formula based on what you have
learned in our naming compounds discussions!
Compound
Sucrose (C12H22O11)
Dextrin (C6H10O5)
Calcium chloride
Citric Acid
Copper (II) Sulfate
Sodium chloride
Description
Relative Melting
Point (time in seconds)
Solubility
Solution
Conductivity
Data Analysis:
1. Using the data from your data table, group compounds into Group 1 Ionic Compounds and Group 2
Covalent Compounds based on physical properties. Then, place the compounds tested into each
group based on these physical properties.
2. Do all members of the group exhibit all the properties? Give specific examples to support your
answer.
Conclusions:
Reject or accept the null based on data and data analysis.
Discuss at least 2 errors that could have occurred or did occur in this lab and how it would directly
affect your results. This must not be “human error” or will not earn credit! You must be specific.
Choose one of the physical properties tested and discuss why ionic compounds differ from covalent
molecules in this properties using chemical concepts. This will most likely require you to read in
your textbook or search on the internet. Don’t forget to cite where you got your information!