Project 11
Identification, Properties, and Synthesis of an Unknown Ionic
Compound
Michelle Pryce
Chemistry 101 Laboratory, Section
Instructor: Sabina Maskey
12 October 2007
My signature below indicates that this document represents my own
work. Excluding shared data, the information, thoughts, and ideas are
my own, except as indicated in the references.
Abstract:
This paper describes the process of indentifying by name and by properties an
unknown ionic compound, and also synthesizing at least 2 grams of the compound
once the identification was made.
The compound was identified as potassium sulfate
by first identifying potassium as the predominate cation and sulfate as the predominate
anion. In addition the compound was mixed with several potential solvents to determine
if the compound was soluble.
in water.
It was determined that the compound was only soluble
Once a solution of the unknown compound was made, its pH as well as
its conductivity was tested.
It was concluded that the pH was relatively neutral and
that it was indeed a conductor of electricity.
A solid sample of the unknown was
burned to observe if the flame displayed any coloration and the flame did display a
low intensity pale violet color.
In addition, tests were conducted to determine if the
compound made any precipitate and if so, with what other product.
Once the
compound was identified as potassium sulfate, an attempt was made to synthesize
potassium sulfate from potassium hydroxide and sulfuric acid.
The attempt was
successful as 3.1 grams were made out of a possible 3.5 grams.
Introduction:
The goal of the laboratory project was to 1) identify an unknown
ionic compound, 2) discover as many physical and chemical properties of the
compound as possible, and 3) devise two syntheses of the compound, and compare
them for cost effectiveness, safety, and potential yield of the compound (Cooper, 117).
It was important that the compound be indentified correctly so that the neighborhood
landfill can be clean-up appropriately with the least amount of harm done to the
environment now and in the future.
Results:
Table 1, Physical Properties
Appearance of compound
Smell
Density
Cylindrical small white crystalloid, double
sided pyramid, hard
No smell
2.66 g/L
Melting Point
Molar Mass
1067-1072 C
174.26 g/mol
Table 2, Solubility Properties
Solvent
Soluble?
Color of Solution
NaOH
HCl
Toluene
Acetone
H2O
Partially soluble
No
No
No
Yes
Cloudy, clear
Clear
Clear
Clear
Clear
Table 3 Analysis of Anions
Known Anion
Expected Result
if anion present
Results
Conclusion
Chloride
Solid white
precipitant
No reaction
Not present
Nitrate
Brown ring at top
of solution,
increase in temp
No reaction
Not present
Sulfate
Milky, white
precipitate
Milky, white
precipitate
formed
Present
Acetate
Cloudy white fruity
smell
No reaction
Not present
Carbonate
Bubbly effervesce
No reaction
Not present
Iodide
Purple color in
solution
No reaction
Not present
Table 4 Analysis of Cations
Ammonium Test
Solution
Results
1mL of 6M Na OH to 1mL of solution
Smell: none detected
pH: no change (neutral)
Table 5 Flame Test
Test #
Color change if any
Intensity
1
Reddish purple
Low/medium
2
Pale violet
Low
3
Pale violet
Low
Table 6 pH test
Test #
1 (orange)
2 (orange)
Results
Bright yellow
Bright yellow
Table 7 Conductivity Test
Voltmeter Reading
Conductor?
0.678
Yes
0.675
Yes
0.679
Yes
Table 8 Gravimetric Analysis
Sample
Mass of dry
sample
Mass of
precipitate
Total mass
Unknown 1
0.491g
0.018g
.509g
Unknown 2
0.504g
0.010g
.497g
Unknown 3
0.487g
0.013g
.517g
Unknown 4
0.474g
0.017g
.491g
Unknown 5
0.501g
0.015g
.516g
Discussion:
The unknown compound was composed of white, tubular, cylindrical crystals.
The compound had the physical properties as described in Table 1.
Solubility tests
indicated that the compound dissolved completely in water and only partially in sodium
hydroxide as indicated in Table 2.
Solubility, even partially, in sodium hydroxide,
which is a strong base, indicates that the compound must have some acidic properties.
The solution was tested with pH paper to determine its pH.
According to the pH
paper, the solution was almost neutral, which indicated a relatively weak acid.
Tests
were conducted in order to determine which anion was present in the compound as
indicated in Table 3. Since the solution produced a milky white precipitate it was
determined that it could be either acetate or sulfate, but since it produced no smell as
would be expected if it were acetate, it was concluded that the anion present was
sulfate.
Then test were conducted to determine which cation was present along with
the sulfate. Table 4 indicates that when 1mL of 6M NaOH was mixed with 1mL of
a
the unknown solution it produce no detectable odor.
solution was tested with pH paper.
In addition the NaOH/unknown
Two separate tests, Table 6, indicated a color
change from orange to bright yellow on the pH paper leading to the conclusion that
the solution was in fact neutral.
The results of the flame test to indicate the
presence of certain cation are summarized in Table 5. Test 1 produced a low to
medium intensity reddish violet flame indicating possible presence of calcium or
potassium.
Since this test was inconclusive, it was repeated.
intensity pale violet flame indicating that potassium was present.
Test 2 produced a low
The test was
repeated one more time to confirm that potassium was the cation present.
Test 3
produced the same results as test 2 leading to the conclusion that potassium was
indeed the cation present.
The solution was then tested for conductivity by placing
the leads of the voltmeter into the solution.
The readings on the voltmeter were
0.678, 0.675, and 0.679 as presented in table 7 indicated that it was a conductor of
electricity.
After identification was made, an attempt was made to synthesize potassium sulfate.
Potassium hydroxide and sulfuric acid were combined to produce potassium sulfate and
water.
It was calculated that 3.5g of potassium sulfate could be made using 2.24g of
potassium hydroxide and 1.96g sulfuric acid.
It actually, 3.1g of potassium sulfate was
made after the excess water was evaporated giving a 88.6% yield.
Conclusion:
It was concluded that the unknown ionic compound (#18) was potassium sulfate
by identifying the presence of potassium (cation test, flame test, ammonium test, and
conductivity test) and sulfate (anion test).
It was further concluded that the pH was
relatively neutral, that the unknown solution conducted electricity, and that the
compound was only completely soluble in water.
Experimental Procedure:
Solubility Test (Qualitative)
A small amount (2 scoops) of the unknown compound was added to 5mL of
the solvent in a test tube.
The tube was shaken to allow for dissolving.
After
shaking the tube for approximately thirty (30) seconds, the tube was observed to see
if any of the solid had dissolved.
The solvents used were distilled water (1), acetone
(2), toluene (3), sodium hydroxide (NaOH) (4), and hydrochloric acid (HCl) (5).
The
unknown compound was completely soluble in water and partially soluble in sodium
hydroxide. The water solution remained clear with the dissolved compound in it.
The
sodium hydroxide solution turned cloudy, and the remaining solvents remained clear
with the unknown compound non-dissolved at the bottom of the tube.
it was deduced that the unknown compound was an ionic compound.
From this test
Solubility Test (Quantitative)
A small amount (500mg) of the unknown was added to 20mL of water
contained in an Erlenmeyer flask.
The flask was heated and a watch glass was
placed on top of the flask and the solution was cool.
allowed to dry, and weighed.
The solution was cooled,
The mass of the dry filter was 0.463g and the mass of
the dissolved solution was 0.613g meaning that that mass of the dissolved compound
was 150 mg.
Flame test:
A clean nichrome wire was heated by flame.
A small amount of the
unknown compound was placed on the loop at the end of the wire.
then heated by the Bunsen flame.
The color of the flame was then compared to the
table on pg 63 of the laboratory manual.
A reddish-violet flame was produced in the
first test indicating the presence of either calcium or potassium.
determined to be inconclusive.
The sample was
This test was
The test was repeated two more times for a total of
three times to ensure the veracity of the results.
The pale purple low intensity flame
of tests two and three allowed for the belief that the unknown compound contained
potassium.
Ammonium Test
One ml of 6M NaCl was added to one (1) ml of the unknown solution.
If a
detectable odor was present, it would have indicated that an ammonium ion was
present, but since the mixture had no odor, it was concluded that the unknown
compound did not contain ammonium ions.
Anion Test
Twenty four (24) ml of water and 6 scoops of unknown salt were mixed together in a
beaker and were shaken to form a solution.
The resulting solution was then evenly
divided into six (6) test tubes to be mixed with various known solvents to determine
the presence of certain anions.
to test tube 1.
A small amount of silver nitrate (Ag[NO3]) was added
If chloride was present, a solid white precipitate should have
developed, but since there was no reaction, it was concluded that chloride was not
present in solution. For the next test, a small amount of sulfuric acid [H2(SO4)] was
added to the solution in test tube 2.
was floated on to the mixture.
Then a small amount of iron sulfide [Fe(SO4)]
If a nitrate was present the expected reaction would
have produced a brown ring at the junction of the two liquids.
one mL of 6M HCl
In test tube three,
(hydrochloric acid) and one mL of BaCl2 (barium chloride) was
added to one mL of the unknown solution . The presence of the sulfate ion was
indicated by the formation of a solid white precipitate.
In test tube four, one mL of
carbon tetrachloride and chlorine water was added to the unknown solution.
The
presence of the color purple would have indicated the presence of the iodide ion, but
since there was no reaction, it was determined that iodide was not present in solution.
In test tube five, 6M HCl was added drop by drop to the solution.
the solution was examined for effervescence.
Since the solution did not effervesce, it
was determined that carbonate was not present in solution.
In the final test tube, six,
one drop of concentrated sulfuric acid was added to the solution.
ethanol was added.
After each drop,
The solution was heated in a water bath.
Then one mL of
If a fruity smell had
been present, it would have indicated the presence of acetate, but since there was no
fruity smell present, it was determined that acetone was not present in solution.
pH Test
A solution of the unknown mixture was made.
conductivity.
A voltmeter was used to determined
The leads of the voltmeter were placed in solution, and the reading was
measured as shown in Table 7.
Synthesis of Potassium Sulfate
After determining what the unknown compound was, the next goal was to synthesize at
least 2 grams of it.
By using potassium hydroxide (KOH) and sulfuric acid (H2[
SO4]), potassium sulfate (K2[SO4]) and water (H2O) were made.
The water was
boiled off leaving only potassium sulfate.
2KOH + H_2SO_4
K_2SO_4 + H_2O
It was determined 2.244g of potassium hydroxide and 1.96g of sulfuric acid would
produce a theoretical yield of 3.5g of potassium sulfate.
It the actual synthesis of
potassium sulfate, a total of 3.1g was made giving a 88.6% yield.
References:
Cooper, M M. Cooperative Chemistry Laboratory Manual. 3rd
edition, 2005.
Periodic Table of the Elements. SparkCharts. 2002.
www.amazingrust.com
www.msds.com
www.wikipedia.com ‘Potassium Sulfate’