Lab: Synthesis of Ionic and Covalent Compounds
An ester is an organic compound that is formed when a carboxylic acid reacts with an alcohol. In addition
to an ester being formed, water is another product of the reactions.
Esterification typically requires a catalyst to speed the reaction. Concentrated sulfuric acid (H2SO4) is a
common catalyst. H2SO4, however, is a very dangerous chemical which can cause severe chemical burns
when in contact with all human tissues.
When carboxylic acids are esterified, some of the resulting esters are aromatic compounds, or
compounds with scents or flavors. Methylsalicylate (oil of wintergreen) is an ester in which the carboxyl
group of salicylic acid has reacted with the alcohol group of methyl alcohol. Oil of wintergreen is used as
both a topical analgesic in rubs for sore muscles and a flavoring agent.
Polymerzation is the process of chemically bonding monomers to form polymers. There are many
biological polymers, such as DNA, proteins, carbohydrates, and lipids. Synthetic polymers are man-made
polymers made from petrochemicals, or molecules found in petroleum. Polymers are often learned
about in a branch of chemistry called organic chemistry. Organic chemistry studies carbon based
compounds.
Polyvinyl alcohol (PVA) and glue are two short chain polymers. Borax is an ionic compound that, when
added, cross-links the short chain polymers. When short chain polymers crosslink, they form an
irreversible gel-like reaction. This same type of reaction is used to create rubber and other soft
compounds.
Synthesis of Wintergreen
1. Weigh out 2.0 g salicylic acid in a large test tube.
2. Add 4.5 ml of methanol to the test tube. Swirl the test tube to mix the contents.
3. Carefully add 4 ml of 3M sulfuric acid to the test tube. Again, gently swirl the test tube to mix the
contents.
4. Place the test tube in a hot water bath approx 55C.
5. After approx 20 minutes of heating, cautiously remove the test tube and sniff the vapors. DO NOT
BOIL THE ACID SOLUTION!
Synthesis of Long Chain Polymers
1.
2.
3.
4.
5.
In a small paper cup, add 20 ml of Polyvinyl Alcohol. You may add food color if you want.
Add approx 4 ml of borax.
Using a wooden splint, stir well. Take the slime out of the cup and knead for several minutes.
Too sticky? Add borax.
Too crumbly? Add PVA
Procedure B
1.
2.
3.
4.
5.
Fill a small paper cup approx. 1/3 full with school glue. You may add food color if you want.
Add 7 ml of borax solution to the glue.
Using a wooden splint, stir well. Take the slime out of the cup and knead it for several minutes.
Too sticky? Add borax.
Too Stringy? Add glue.
Synthesis of Alum
1. Weigh out about 1 gram of aluminum foil to the nearest centigram. Tear the foil into small pieces
and place in a 250 ml beaker.
2. Slowly add 25 mL of 3 M KOH solution. Allow the reaction to proceed until all of the foil is
dissolved. Remove any undissolved solids such as carbon particles by filtering the solution
through a Buchner funnel while the solution is still hot. Rinse the filter paper with a small amount
of distilled water.
3. At this point, the solution contains [Al(OH4)]- and K+ ions, along with OH- ions. Cool the solution
and then acidify it SLOWLY, with constant stirring using 35 ml 3M H2SO4. The solution will get
very hot because you are adding strong acid to the strongly basic solution. Solid Al(OH)3 will first
precipitate and then dissolve as more H2SO4 is added. If a precipitate still remains, filter the
solution and discard the solids. You can use vacuum filtration with the Buchner funnel and filter
flask to speed up this process. Then boil the solution until water has evaporated to give a volume
of about 50 ml of solution. Cool the solution and cover the beaker with Parafilm. Allow to rest
undisturbed.
4. Cool the solution in an ice bath for 15 minutes, keeping it as motionless as possible. Crystals of
alum should grow in the beaker. If no crystals form, scrape the bottom of the beaker with a
stirring rod to create a rough place where crystals may begin to grow, or add a seed crystal. If
there are still no crystals, reheat the solution until more water has evaporated and then cool again.
Rapid cooling in an ice bath causes very small crystals to grow; slow overnight cooling allows the
formation of larger crystals. Collect the alum crystals by vacuum filtration. Wash the crystals with
about 50 mL of a 50% by volume water and ethanol mixture, in which alum crystals are not very
soluble. Allow the crystals to dry at room temperature. Determine the mass of the alum.
Calculate the theoretical yield of alum assuming that aluminum was the limiting reactant and the
foil was 100% aluminum, and calculate your percent yield.