Laboratory work
Chemical bonding
Purpose of the work:
The purpose of this lab
is to compare the properties of ionic and covalent compounds.
Materials:
·
6 test tubes with test tube rack
·
Bunsen Burner
·
Microtitration plate
·
Distilled water
·
Wooden splints
·
Conductivity meter
·
Ethanol
·
Sodium chloride NaCl
·
Oxalic Acid C2H2O4
·
Cobalt (II) sulfate CoSO4
·
Nickel (II) chloride NiCl2
·
Starch C6H10O5
·
Sucrose C12H22O11
Procedures:
1.
Place six test tubes in a test tube rack and add a few crystals of
each substance (see chart for substances) to a different test tube. Make sure to
label what is in each test tube by placing a paper underneath the rack or your
own method. Record their description and the chemical formula in the table.
2.
Take each test tube and hold over a Bunsen Burner watching the clock
to determine how long it takes to start to melt. Maximum time should be 2
minutes. It is very important that you remove the test tube from the heat as
soon as it starts to melt; otherwise you will not be able to clean it out.
Record the time it started to melt or that it did not melt in data table.
3.
Using a microtitration plate add a few crystals of each substance to
its own spot making sure to label on a paper where they are located or use the
numbering system that may be on the plate. Add distilled water until it is
almost to the top of the depression and stir with a wooden splint; record if the
substance dissolves. Do not discard, as you will need them for number four.
4.
Using conductivity meter check each sample from number three, record
your results by counting the number of blinks per twenty seconds. Clean meter in
between each chemical.
5.
Repeat step number three replacing water with ethanol. Do not do step
number four with the ethanol.
6.
Clean up, everything can be rinsed down the sink, wash all items with
soap. Put everything away where you got it.
Questions:
1.
Determine which of the groups consists of ionic compounds and which
consists of molecular compounds.
a)
Write a general statement to summarize the properties of ionic
compounds. Include state at room temperature, melting pint, conductivity of
aqueous solution, and solubility in water.
b)
b. Write another general statement to summarize the properties of
molecular compounds. Include state
at room temperature, melting pint, conductivity of aqueous solution, and
solubility in water.
2.
How is melting point related to the strength of attractive forces
between the particles of a compound?
Which are stronger, ionic bonds or intermolecular forces? Which have higher melting points, ionic
compounds or molecular compounds?
3.
Compare and contrast the appearance of covalent and ionic
compounds. When observing the
substances with the hand lens, what properties do you notice that you could not
see with your naked eye?
4.
Imagine looking at the substances under a microscope. What do you
think the substances might look like on that level?