Properties of Ionic and Covalent 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 nonmetallic 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 a scientist distinguish ionic from covalent
compounds. 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.
The purpose of this experiment is to observe several properties of some ionic and some covalent compounds
and attempt to recognize patterns among the properties. The patterns you may recognize are generalizations and may not necessarily apply to all
ionic and covalent compounds.
Objectives
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●
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Classify compounds as either primarily ionic or primarily covalent from the name, formula and the behavior of the compounds.
Observe and record some properties of several ionic and covalent compounds.
Recognize patterns among the properties and distinguish ionic compounds from covalent compounds.
Materials
goggles
apron
2, 12-well plates
spatula
methanol, CH3OH
distilled water
toothpicks
conductivity tester
Chemicals
A. sodium chloride, NaCl
B. potassium chloride, KCl
C. sodium sulfate, Na2SO4
E. sucrose, C12H22O11
F. benzoic acid, C6H5COOH
G. acetaminophen, C8H9NO2
D. potassium iodide, KI
Procedure
Part 1: Melting Point
1. Put on your goggles and apron.
2. Get an aluminum foil tray and draw seven (7) wedge shapes on it. Label the wedges A, B, C, D, E, F and G, as below.
B
3.
4.
5.
6.
C
Place a SMALL sample of each substance in the appropriate wedge of your foil.
Place the foil on a hot plate and turn it on high.
After a few minutes, observe each section and record on a chart, which substances have melted and in which order.
Turn off the hot plate.
Part 2: Solubility in Water
1. Clean your two spot plates with soap and water. Dry them thoroughly.
2. Lay the spot plates side by side on a piece of paper so that you have eight columns. As you add the substances, label the piece of paper so
it is clear what substance is in what column and row.
3. Using a spatula, place a grain-of-rice sized sample of sodium down the first column in the first two rows. Leave the fourth row empty.
4. Repeat step 3 using each of the remaining compounds, B through F.
5. To the first row, add several drops of distilled water to each well, enough to nearly fill the well with water. Stir with a toothpick and observe
the relative solubility of each of the solids. Record observations in the data table.
Part 3: Solubility in Methanol
1. To the second row, add several drops of methanol to each well, enough to nearly fill the well with water. Stir with a toothpick and observe the
relative solubility of each of the solids. Record observations in the data table.
Part 4: Conductivity
1. To the third row, add equal amounts of methanol and distilled water. Stir with a toothpick. Test the resulting solutions with the conductivity
tester. Record observations in the data table.
2. Wash your spot plate with soap and water to remove all chemicals. Wash your hands thoroughly with soap and water. Wipe down your lab
table with a wet paper towel.
Ionic/Covalent Compounds Lab Data
*** Make sure to indicate the extent a substance melts or dissolves: Completely, partially, not at all. ***
Substance
Color
Melts or not
Dissolves in
water
Dissolves in
methanol
Conductivity
Melting point
sodium chloride
122.4 oC
potassium
chloride
708 oC
sodium sulfate
37 oC
sucrose
686 oC
dextrose
884 oC
benzoic acid
185 oC
acetaminophen
169 oC
Analysis and Conclusions
1. Determine, based on its chemical formula (you will have to look some of them up), whether each of the substances used is covalent or ionic.
benzoic acid
_________________________
potassium iodide
_________________________
magnesium chloride
_________________________
sodium sulfate
_________________________
glycerol
_________________________
sucrose
_________________________
2. Look carefully at your results. Do you see any patterns? Summarize the results for all four columns of your data table for ionic compounds and
covalent compounds. If you don’t see any patterns, state “no pattern”. If you see general patterns, state them.
Ionic
Melting Point
Dissolves in Water
Dissolves in Methanol
Conductivity
3. Predict the following, based on patterns established in this experiment:
a. What would you expect the solubility of sodium iodide in water to be?
b. What would you expect the relative melting point of sodium iodide to be?
c. What would you expect the conductivity of a glucose solution to be?
4. How can you explain the fair, poor, and non-conductors of electricity through the explanation of bond types?
Covalent
Analysis and Conclusions
2. Determine, based on your lab results, whether each of the substances used is covalent or ionic.
a. benzoic acid
Covalent
b.
magnesium chloride
Ionic
c.
glycerol
Covalent
d.
potassium iodide
Ionic
e.
sodium sulfate
Ionic
f.
sucrose
Covalent
3. Look carefully at your results. Do you see any patterns? Summarize the results for all four columns of your data table for ionic compounds and
covalent compounds. If you don’t see any patterns, state “no pattern”. If you see general patterns, state them.
Ionic
Covalent
Melting Point
Does not Melt
Melts Quickly
Dissolves in Water
Dissolves in Water
Sometimes dissolves in water
High Conductivity
No Conductivity
Dissolves in Methanol
Conductivity
5. Predict the following, based on patterns established in this experiment:
a. What would you expect the solubility of sodium iodide in water to be?
i.
Sodium iodide - or NaI - would be an ionic compound (since it is composed of a metal and a nonmetal). As a result, I
would expect it to dissolve very well in water since ionic compounds have good water solubility.
b. What would you expect the relative melting point of sodium iodide to be?
i.
Again, sodium iodide would be an ionic compound. As a result, it would have a very high melting point since most
ionic compounds have very high melting points.
c. What would you expect the conductivity of a glucose solution to be?
i.
Glucose would not conduct electricity. Since glucose is a covalent compound, it would not dissociate into ions when
dissolved in water. As a result, glucose would be considered a nonelectrolyte and would have no electrical
conductivity.
6. How can you explain the fair, poor, and non-conductors of electricity through the explanation of bond types?
a. When compounds completely dissociate into ions, or form many ions when dissolved in water, they will conduct electricity
very well. Likely, compounds that dissociate into relatively few ions, or only partially dissociate will conduct electricity more
poorly. Compounds that dissociate into ions are formed with ionic bonds. Compounds that don’t dissociate, like covalent
compounds, will not conduct electricity because there are no ions in solution.