Keywords: identify compound, quantitative, qualitative, measuring
Chemistry 101 Laboratory Section
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The purpose of this experiment was to identify the unknown compound. The tests that were done to determine the identity of the compound include qualitative solubility tests, quantitative solubility tests, measuring solution conductivity, anion and cation test, flame test, and formation of precipitate. It was found that the compound had no smell, was soluble in water, and not soluble in toluene and acetone. The ions dissociated in the water, creating conductivity. When the ammonia test was performed no ammonia smell was produced. The flame test yielded a color that matched that of sodium bicarbonate indicating that the unknown compound contained sodium. The anion test for chloride proved to be positive, resulting in the summation that the unknown compound was sodium chloride.
The group is employed by an Environmental Protection Agency to indentify a compound in the landfill in your home town. The group must also discover as many chemical and physical properties of the compound as we can. We need to devise two syntheses of the compound, and compare them for cost effectiveness, safety, and potential yield of the compound. To identify the compound, the physical properties (smell, color, and state) need to be established. Next, the qualitative solubility of the compound was tested in water, toluene, and acetone, which would determine whether the compound would dissolve from rain water or other chemicals that may be present in the landfill and create runoff. Conductivity was also tested with a voltmeter in order to determine whether or not the compound would be dangerous when dissolved in water. If the compound was conductive it would dissolve in water and produce an electric current. The flame test was performed to specify one of the elements. A solution of water and the element was used to place the nichrome wire in, and then the nichrome wire is placed into the flame. If the flame produces a color it is indicative of a certain metalloid ion or metal. A color is produced in the flame when the heat of the flame changes the metal ions into atoms which then become excited and produce light that can be seen with the naked eye. It is also important to analyze the presence of certain cations and anions using tests that identify the presence of the anions chloride and sulfate, and the presence of the cation ammonium. The anion tests for chloride and sulfate prove to be positive when a white precipitate forms and the ammonium test proves to be positive when an ammonium smell is produced. After all of the physical and chemical tests were performed, a solution of the unknown compound and a solution of what was deduced to be unknown compound were reacted with an acid (nitric acid), a base (potassium hydroxide), silver nitrate, potassium sulfate, and potassium nitrate in order to determine if they produce the same results. Gravimetric filtration was then performed with the known and unknown substance. A precipitate was formed using silver nitrate, which could then be weighed. After the filtration process, the unknown compound was then synthesized to produce a percent yield.
TABLE 1 Physical Properties Test
State of Matter
Solubility in Water
TABLE 2 Anion Tests
Test for Chloride
White Precipitate Formed
Test for Sulfate
Test for Nitrate
No Brown Ring
Test for Carbonate
Test for Acetate
TABLE 3 Cation Tests
Test for Ammonium
NH4Cl + NaOH à Ammonium Smell
Bright Orange/Yellow Flame
TABLE 4 Reaction Tests
Type of Reaction
NaCl(aq) + HNO3(aq) -> NaNO3(aq) + HCl (aq)
NaCl(aq) + KOH(aq) -> NaOH(aq) + KCl(aq)
NaCl (aq)+ AgNO3 (aq)-> AgCl (aq)+ NaO3(aq)
NaCl(aq) + K2SO4(aq) -> Na2SO4(aq) + 2 KCl(aq)
NaCl (aq) + KNO3(aq) -> NaNO3(aq) + KCl(aq)
TABLE 5 Gravimetric Analysis
NaCl (aq) + AgNO3 (aq) -> AgCl (s) + NaNO3 (aq)
Vacuum Filtration Trial #
Amount of Precipitate Produced (grams)
Known Trial 1
Known Trial 2
Unknown Trial 1
Unknown Trial 2
Unknown Trial 3
TABLE 6 Synthesis Reaction
Amount Produced (grams)
Theoretical Yield (grams)
HCl (aq) + NaOH (aq)à NaCl (s) + H2O (l)
First, the physical properties of the unknown compound were observed and recorded. It was found that the compound was crystalline in structure, a solid, white, with no odor (Table 1). All of these properties suggest that the compound was ionic because ionic compounds do not have a distinct odor and are solid at room temperature because of their high melting points. The unknown compound was then tested for solubility in water, toluene and acetone. The compound was soluble in water, indicating the compound was a polar or ionic compound, and not soluble in toluene or acetone which eliminates it being polar or nonpolar. Therefore, this points to the compound being ionic. After the compound was dissolved in water, the conductivity was tested with a voltmeter, which produced a voltage of 0.35 volts proving that the substance is conductive since it is over 0.1 volts. This further proves that the unknown compound was ionic since only ionic compounds dissociate in water and create an electric current.
The flame test was performed to determine one of the elements in the compound. Four known compounds, sodium bicarbonate, magnesium nitrate, calcium sulfate, and potassium nitrate were put under the flame test to compare the unknown to. When the unknown compound was put under the flame test it produced the same color as sodium bicarbonate, bright orange/yellow, indicating the presence of sodium (Table 3). The ammonium test was also performed to verify that the compound did not contain ammonia. No smell was produced when the unknown solution and sodium hydroxide were mixed, and a smell would indicate the presence of ammonia. Therefore, the compound was proven to contain sodium. When the anion tests for chloride and sulfate were performed, a white precipitate was produced from the chloride test, indicating the presence of chloride while the sulfate reaction created no precipitate indicating the absence of sulfate (Table 2).
In addition, the unknown compound was put through a series of reactions along with what was believed to be the compound in order to compare the reactions to determine if they produce the same reactions. First sodium chloride, what is believed to be the unknown compound, and the unknown compound were reacted with silver nitrate, which produced a precipitate because it was a double displacement that produced AgCl which is not soluble in water. Sodium chloride and the unknown compound were reacted with potassium sulfate but produced no reaction because the products sodium sulfate and potassium chloride are both soluble in water. Sodium chloride and the unknown compound were then also reacted with potassium nitrate, creating a double displacement reaction which produces sodium nitrate and potassium chloride, which are also both soluble in water, therefore producing no reaction. When sodium chloride and the unknown compound were reacted with an acid, nitric acid, but the presence of the sodium chloride did not affect the pH of the nitric acid because it was an ionic compound. When the sodium chloride and the unknown compound were reacted with a base, potassium hydroxide, there was also no reaction or change in the pH of the potassium hydroxide because the sodium chloride is an ionic compound. Both the sodium chloride and the unknown compound produced the same results in every reaction further proving that they are one in the same (Table 4).
Once it was found that sodium chloride and silver nitrate produce a precipitate when reacted, the reaction was used to produce a certain amount of precipitate which was then used in gravimetric analysis to see if both the known and unknown compound would produce the same amount of precipitate. The reaction that was filtrated was NaCl(aq) + AgNO3 (aq) -> AgCl (s) + NaO3(aq). The results from the known reaction were 1.77 grams of filter paper and 1.081 grams of precipitate alone, while the theoretical yield was 1.225 grams. The unknown reaction has yet to be found. The percent yield for the reaction was 97.56% (Table 5).
A synthesis reaction was the final test preformed. The following chemical reaction occurred: HCl(aq) + NaOH(aq) à NaCl(s) + H2O(l). Once all of the water was evaporated out with the use of a hot plate, the precipitate was able to be weighed and the percent yield could be calculated. The reaction had a percent yield of 98.55% (Table 6).
After being employed by the Environmental Protection Agency, the group was able to identify the compound in the landfill. After all of the tests and reactions were performed, it was found that the unknown compound was sodium chloride. Its solubility in water, conductivity, and crystalline structure points to the fact that the compound is ionic. The positive flame test for sodium indicates that sodium is one of the elements in the compound because it produced a bright orange flame. The positive chloride test, when a white precipitate was formed, indicates that chloride is the second element in the compound. The unknown compound and sodium chloride were put through the same reactions and consistently produced the same results, further indicating that the unknown compound is sodium chloride. The gravitational analysis of the known and unknown substances provided similar results, backing up that the unknown substance was sodium chloride. The synthesis reaction produced a percent yield of 95.05%.
Physical Properties Tests
1. The physical state of the unknown compound was observed. This included the state of matter, smell (using the wafting technique), color, and structure.
2. A small amount of the unknown compound was placed in approximately 50mL of water and stirred to see if it would dissolve.
3. The same solution was used for the voltmeter and the conductivity was recorded.
Chloride Ion Test
Approximately 1 mL of the unknown solution was placed in a test tube and 1 mL of 6 M HNO3 was added. After that another 1 mL of AgNO3 was added. Whether a white precipitate was formed or not was recorded. If a white precipitate is observed, a chloride ion is present in the solution.
Sulfate Ion Test
Approximately 1 mL of the unknown solution was placed into a test tube and 1 mL of 6 M HCl was added. After that another 1 mL of BaCl2 solution was added to the same test tube. Whether or not a white precipitate formed was recorded. If a white precipitate is formed, sulfate is present in the solution.
1. The heat from the Bunsen flame was used to cleanse the nichrome wire.
2. A small amount of the unknown compound was placed onto the nichrome wire and held over the flame. The color of the flame was observed.
Approximately 1 mL of 6 M NaOH was added to 1 mL of the unknown compound solution. The waft technique was used to detect if there was any odor. If the smell of ammonia was present, there were ammonium ions present in the solution.
Reaction with an Acid
A solution with a small amount of unknown compound was mixed in 50 mL of water and a separate solution of a small amount of ammonium chloride and 50 mL of water. A small amount of the two solutions were placed in to two separate test tubes and a small amount of HNO3.
Double Displacement Reaction
A solution of a small amount of unknown compound was placed into 50 mL of water and a separate solution containing a small amount of sodium chloride and 50 mL of water. A small amount of the two solutions was placed into two separate test tubes and a small amount of K2SO4 was added into each test tube. The test tubes were then swirled and mixed.
Double Displacement Reaction
A solution of a small amount of unknown compound was mixed with a solution of 50 mL of water and a separate solution of a small amount of sodium chloride and 50 mL of water. A small amount of the two solutions were placed into two separate test tubes and a small amount of AgNO3 was added into each of the test tubes. The test tubes were then swirled and mixed.
Double Displacement Reaction
A solution of a small amount of unknown compound was mixed in 50 mL of water and a separate solution of a small amount of sodium chloride and 50 mL of water. A small amount of the two solutions were then placed into two separate test tubes and a small amount of KNO3 was added to each test tube. The test tubes were then swirled and mixed, and whether or not a reaction occurred was recorded.
Reaction with a Base
A small amount of unknown compound was mixed with 50 mL of water and a separate solution of a small amount of ammonium chloride and 50 mL of water. A small amount of these two solutions were then placed into two separate test tubes and a small amount of KOH was added.
1. A Buchner flask was used with a funnel placed over the top.
2. The filter paper was weighed and then wetted with water slightly.
3. The solution containing the precipitate was poured onto the filter paper and left until most of the liquid had seeped through.
4. The filter was then removed from the funnel and placed into an oven for 10 minutes until the precipitate and paper had completely dried.
5. The filter paper was then weighed with the precipitate still on top. The weight of the filer paper was subtracted from the new weight to obtain the most accurate result.
6. The procedure was completed three times with the unknown substances and twice with a known substance.
1. Approximately 12.3 mL of ammonium hydroxide was mixed with 6.2 mL of hydrochloric acid in a beaker.
2. The solution was placed on a hot plate (under a hood) and allowed to boil until all of the liquid evaporated.
3. The remaining precipitate was removed from the beaker and weighed.
Cooper, M. M., Cooperative Chemistry Laboratories, McGraw- Hill: New York, NY, 2008.