Identification and Synthesis of Unknown Compound 829pBy Tyler Blevins

Group members: John Creps, Ashley Gergen, Alison Werneiwski

Abstract: An unlabeled container of a white compound was discovered in the chemistry

stockroom. In order to dispose of the substance safely, the identity as well as the chemical and

physical properties of the compound needs to be identified. The identity of the unknown white

compound (UWC) has been narrowed down to a list of 15 different compounds. There was 5

grams of the UWC that was available for testing. Various tests, such as solubility test,

conductivity test, pH test, ion test, and flame test, were used to determine the properties of the

unknown compound. The results from the tests were used to compare the properties of the UWC

to the properties of the possible compounds for identification purposes. The tests indicated that

compound 829p is potassium sulfate. Once the identity of the UWC was discovered, the

compound was synthesized and tested to compare its properties to those of the UWC in order to

verify that they are the same compounds. Potassium sulfate was successfully synthesized and the

testing confirmed that its properties were an exact match to those of 829p.

Introduction: During an inventory check of the chemistry stockroom, an unlabeled container

was discovered and its contents were unknown. In order to properly dispose of the unknown

compound, its identity and chemical and physical properties needed to be investigated. Proper

disposal of compounds is very important because they can potentially have harmful effects on

their surroundings. Not all compounds are safe to pour down the sink because it’s possible that

they could react with other compounds and produce toxic gases and byproducts. Therefore,

identifying unknown chemical substances and properly disposing of them is an extremely

important branch of science. Using a wide variety of tests to identify an unknown substance can

show if the substance is toxic, dangerous, highly reactive, difficult or easy to dispose of and

many other useful properties the substance possesses. In everyday life, this practice can be

helpful in cleaning chemical spills, identifying compounds such as the salt that forms in a pan

when water is boiled, preventing corrosion in pipes, and creating fragrances. This practice has

even been used to identify a compound that mimics one of the brains growth factors that protects

brain cells from damage. In this lab, 5 grams of an unknown white compound was discovered

and its identity was narrowed down to a list of 15 compounds, all of which look similar. The 15

compounds include CaCO3, MgSO4, NaC2H3O2, CaCl2, KCl, Na2CO3, Ca(NO3)2, KNO3, NaCl,

MgCl2, Na2SO4, NH4Cl, K2SO4, (NH4)2SO4, and K2CO3. Because they look similar, stating a

hypothesis is difficult. In the remainder of this report, the process and results for the

identification and synthesis of the unknown white compound are explained in detail.

Experimental and Results: The experiment to identify and synthesize the unknown compound

was broken up into three days. On the first day of the experiment, multiple tests were performed.

Our group decided that we would first try to narrow down which of the suspected compounds

matched the unknown compound by comparing their physical traits. We noted that our unknown

compound had a texture that was more similar to that of sugar as opposed to powder like many

of the compounds. The 15 possible compounds were analyzed and the texture of the unknown

compound matched the texture of 3 of them. The compounds that matched the texture of the

UWC were Na2SO4, K2SO4, and NaCl. For the remainder of day one, the three suspected

compounds and the UWC were tested in various ways, the first of which was the solubility test.

For the solubility test, four 50 mL beakers were filled with 25 mL of deionized water and a small

amount of 829p, Na2SO4, K2SO4, and NaCl was placed in its respective beaker. The compound

and water in the beakers were stirred using a stirring rod and the solubility of the mixture was

recorded. All four of the mixtures were soluble, so the list was not narrowed down from the

solubility test. Directly following the solubility test, the conductivity test was performed. Using

four clean beakers, 100 mL of deionized water was poured into each one. Next, a digital scale

was used to measure out .75g of each of the four compounds and they were each placed in their

own beaker. A stirring rod was used to create an aqueous solution in each of the beakers. Using a

conductivity probe that was hooked up to a computer that was running a program called

LoggerPro, the conductivity of each of the aqueous solutions was recorded. The results are as

follows:

Na2SO4 K2SO4 NaCl 829p

Conductivity(µS/cm) 3326.0 3324.8 3328.1 3325.5

As the results show, the conductivity of each of the four aqueous solutions is very similar and the

test did not help narrow down a possible match for the UWC. The next test that was performed

was the pH test. The same beakers containing the aqueous solutions used in the conductivity test

were used for the pH test as well. The only difference between the two tests was that in the pH

test, a pH probe was connected to the LoggerPro system instead of a conductivity probe. The

probe was placed in each of the solutions and the pH was recorded. The results were:

Na2SO4 K2SO4 NaCl 829p

pH 5.65 5.75 5.69 5.65

The results of the pH test showed that each of the aqueous solutions was very similar and they

are all fairly neutral. Because the results were so close, we were not able to narrow down the list

of possible matches to the UWC any further. The next test that was performed was the ion test.

Sulfate ions were tested for first. In order to set up the experiment, a test tube rack and one test

tube were retrieved from the lab and set up on the table. The components that were added to the

test tube were 1.0 mL of 6M HCl and 1.0 mL of BaCl2. The next component that was added to

the test tube was 1.0 mL of the unknown solution. Upon mixing the solution, a white precipitate

formed which indicated that the compound 829p contained a sulfate ion. The results for the ion

test for sulfates allowed the list of possible compounds that matched the UWC to be narrowed

down to MgSO4, Na2SO4, K2SO4, and (NH4)2SO4 although it was suspected that the compound

829p was either Na2SO4 or K2SO4.

On day 2 of the UWC experiment, the ion test for sulfates was performed once again in

order to double check that the compound 829p contained sulfate ions. The experiment was

performed under the same conditions and in the same manner as described in the previous

paragraph and the results were the same which meant that the UWC contained a sulfate ion. The

flame test was the next test to be performed. In order to perform the flame test, a Bunsen burner

and nichrome wire were needed. The Bunsen burner was connected to the gas valve using a

rubber hose and it was then lit and adjusted to have a steady flame. In order to make sure that the

nichrome wire was clean before each compound was tested, a test tube of HCl and a test tube of

deionized water were also required. The flame test is performed by dipping the nichrome wire

into the HCl first, and then into the water in order to make sure the results are solely from the

compound being tested. The clean wire is then dipped into the compound being tested and then

held over the flame. Using previous knowledge, we compared the color of the flame from all of

the sulfates to the color of the flame from the 829p compound. The results are as follows.

(NH4)2SO4 Na2SO4 K2SO4 MgSO4 829p

Color No Reaction Bright Yellow Purple/Orange Orange Purple/Orange

The flame test turned out to be a very significant test because the only compound whose color

matched that of the UWC even remotely was K2SO4 and therefore it was concluded that the

compound 829p was, in fact, comprised of potassium sulfate.

The third day of lab was devoted to synthesizing the compound K2SO4. The balanced

chemical equation for synthesizing it was 2KOH (aq) + H2SO4 (aq) => K2SO4 (s) + 2H2O (g).

Once the proper equation was figured out, the amount of each reactant needed was calculated.

The calculations are shown below:

1mole K 2SO 4135.17g K 2SO 4

x 2mole KOH

1mole K2 SO 4x

1.0 L KOH1mole KOH

x 1000mLKOH

1.0 LKOH =

11.5mLKOH1gramK 2 SO 4

1mole K 2SO 4135.17g K 2SO 4

x 1mole H 2 SO 41mole K 2SO 4

x1.0 LH 2SO 41moleH 2SO 4

x 1000mLH 2 SO 4

1.0 LH 2SO 4 =

5.7mLH 2SO 41gramK 2 SO 4

The first step taken in the synthesizing process was to get a 500mL beaker and retrieve a bottle

of KOH and a bottle of H2SO4 from the lab. The reactants were measured out to the values

calculated above in a graduated cylinder and then they were both poured in to the beaker. The pH

of the solution was tested using pH probe and it was 1.76 which is very acidic. In order to

neutralize the solution, KOH was continually added with a pipet until the solution reached a

neutral pH of 6.74. By the time the solution was neutralized, a solid had formed at the bottom of

the beaker. A hot plate was heated up and the beaker was then placed on it in order to boil off the

H2O. When the majority of the water had boiled off and all that was left was the solid K2SO4, the

500mL beaker was placing in the oven for 30 minutes in order the vaporize all of the water

molecules off so that pure K2SO4 was the only product that was left in the beaker. Using a digital

scale the beaker was measured and then the K2SO4 was scraped out into a test tube. The empty

beaker was then weighed again and the mass was subtracted from the first value in order to give

the mass of the K2SO4 synthesized. The chemical reaction created 5.814 grams of K2SO4. The

goal for the synthesis of the compound was to make 1gram of product, but because 6M reactants

were used instead of 1M reactants, the expected mass of the product was 6 grams. The percent

yield of the reaction was then calculated by dividing 5.184 by 6 and multiplying the resulting

number by 100. This equation stated that the percent yield of the reaction was 96.9%. The K2SO4

synthesized in the reaction was then tested in order to make sure that the test results matched the

results of the 829p compound. The solubility test and the flame test were performed in the same

way they were in day 1 and 2. The results of the tests confirmed that the compound created

matched 829p perfectly.

Discussion: The interpretation of the data was mostly done in the previous section. The chemical

and physical properties of the tested compounds have been explained in detail, the results of the

tests and processes taken to find the results have also all been analyzed, and the compound was

identified and synthesized. The compound 829p can now be properly disposed of using the

information gathered during the experiments. One of the main limitations of the data imposed by

the lab was that the only available cation test performed was the flame test. The flame test could

potentially have been contaminated by using the same nichrome wire over and over for different

compounds. Although it was cleaned in between each compound, it is possible that some

compounds could have carried over and affected the results of the compounds tested afterwards.

There was a relatively small amount of errors that could have affected the results of this lab. The

percent yield of the synthesized compound was very high and it may have been even higher had

we gotten absolutely all of the K2SO4 out of the beaker before weighing the results. The majority

of it was definitely retrieved, but it is possible that some was left over in the beaker. Another

source of error was that KOH had to be added to the solution during synthesis in order to raise

the pH level. This means that there was a limiting reactant in the reaction and there was some

KOH left over with the water in the beaker once the solid was formed. This most likely did not

affect the results very much because only the solid was weighed out and the KOH would have

been in liquid form.

Conclusion: The unknown compound underwent various tests and through analysis of the results

of the tests, it was confirmed that compound 829p is K2SO4. During the first part of the

experiment, the unknown compound was narrowed down to 4 compounds, all of which were

sulfates, but it was suspected to be either potassium sulfate or sodium sulfate. Upon further tests

and analysis of the four sulfate compounds, the identity of the unknown white compound was

discovered to be potassium sulfate. Many of the chemical and physical properties of the

unknown compound were discovered and recorded. Once the identity of the compound was

discovered, 5.814 grams of it was synthesized with a 96.9% yield. Overall, this lab was very

successful.

References:

(1) “Flame Colors as Chemical Indicators.” Flame Colors. N.p., n.d. Web.

http://hyperphysics.phy-astr.gsu.edu/hbase/Chemical/flame.html (accessed March 10, 2013)

(2) “Flame Test.” The Columbia Encyclopedia, 6th ed. 2012. Encyclopedia.com.

<http://www.encyclopedia.com>. (accessed March 10, 2013)

(3) “Identification of an Unknown Substance.” CSU Stanislaus Science Web.

http://science.csustan.edu/byrd/chem1002/unknown.htm (accessed March 10, 2013)