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  • Published on: 15th October 2019
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The Discovery of the Identity of an Unknown Ionic Compound and its Confirmation

Introduction:

In this experiment, a group of lab interns are tasked with discovering the identity of an unknown compound in order to properly dispose of the compound. Tests are performed to identify physical and chemical properties of the unknown compound.  

Experimental:

Week 1

First, we looked at the physical properties of our unknown chemical. Then we preformed the solubility test on the unknown compound. Jenna, 1g of the unknown compound in distilled water then used a stir rod to stir the solution. We observed that the compound took a while, but ultimately dissolved in the distilled water, then Maddie and Nnamdi worked to mark off each compound on our list of possible compounds that are not soluble in water. Then we performed a flame test. Nnamdi Soaked a wooden stick in the solution we made from the solubility test. Jenna put the wooden stick under a flame and we observed a bright orange light. Nnamdi and Jenna discovered that our compound contains Na as its cation and proceeded to cross off all compounds from our list of possible compounds that did not contain Na. Then we decided to test for halides, Nnamdi added 1 mL of 1M HNO3 and 1 mL of 0.1M AgNO3 solution to 1 mL of the unknown solution. The test proved negative We then preformed the sulfate test. Nnamdi added 1mL of 3M HCl and 1 mL of 0.1M BaCl2 solution to 1 mL of the unknown solution. This was also negative. We then tried the acetate test Nnamdi placed 2 mL of our unknown solution in a test tube and added 1 drop of conc. sulfuric acid then he added 1 mL of ethanol and heated the solution for a few minutes in a water bath. This test also resulted negatively so we then decided to try the carbonate test. Nnamdi added a few drops of 3M HCl to 1 mL of the unknown solution.  We observed that the solution began to fizz as Nnamdi added the drops which means that the Compound contained Carbonate as its Anion. We concluded that the identity of the solution was Na2CO3. (After each test each solution created was poured into the waste bin. The wooden stick used was placed into a large beaker filled with water.)

Week 2

In order to confirm the identity of the unknown compound we preformed these tests to discover if the unknown and known compounds react the same:

First, we performed Solubility test: Nnamdi filled 2 beakers with distilled water then Jenna put 1g of the unknown compound and 1g of the Na2CO3 into each beaker and used a stir rod to create two solutions. Both compounds slowly dissolved into the solution. We then performed pH Test: Jenna used a pipet to place on drop of each solution onto the pH paper. We observed that the pH paper turned a dark blue color for both the unknown solution and the authentic Na2CO3 Solution. Then we performed the Flame test: Nnamdi places 1 wooden stick into each created solution in order to let the stick soak. After 5 minutes of soaking Nnamdi preformed the flame test on the unknown solution and Maddie preformed the flame test on the authentic solution (both tests were performed by placing the wooden sticks that were soaked in the solution over a lit Bunsen burner). we observed that in both tests there was a bright orange We then performed Carbonate test: Using a 10mL measuring cylinder Nnamdi an Maddie measured out 1mL of the unknown solution and 1mL of the authentic solution and placed each measurement in separate 10mL test tubes. Then Jenna added a few drops of HCl to one test tube and Nnamdi added a few drops of HCl into the other test tube. We observed within Both test tubes that the solution fizzed as the drops were added.

Results:

Week 1

1. Solubility Test: The compound slowly dissolved into the water.

Figure 1. The solution to the right is the authentic Na2CO3 Solution to the left is the unknown compound.

2. Flame Test: Tested positive for Na+ . We observed an orange flame.

Figure 2. flame turned orange when both sticks were placed in the flame.

3. Halides Test: Tested negative for Cl-, Br-, and I-

4. Sulfate Test: Tested negative for SO42-

5. Acetate Test: Tested negative (no smell)

6. Carbonate Test: Tested positive for CO3. We observed small bubbles in both test tubes.

Figure 3. very small bubbles are formed and the solution “fizzes”.

Week 2

There was no need to perform the Acetate Test and the Sulfate test because both tests were negative. Also performing the tests that were positive in week one provided sufficient data/evidence proving that the unknown compounds have the same properties as authentic Na2CO3.

1. Solubility Test: While preforming this test we observed that both compounds slowly dissolved into the distilled water.

2. pH Test: While preforming this test, we observed that the 2 pH papers reacted the same to a drop of each solution. Both papers turned a dark blue color, therefore we concluded that the pH level of the unknown compound was around 10 and the results/ conclusion was the same for the sodium Carbonate.

Figure 4. Both papers appeared to have the same color.

3. Flame Test: While preforming this experiment, we observed a bright orange flame when placing each wooden stick under the flame (one at a time)

4. Carbonate Test: We observed a fizz after adding a few drops of 3M HCl to 1mL of the unknown solution and to 1mL of the authentic solution.

Discussion:

Claim:

The unknown compound is identified and confirmed to be Na2CO3.¬

Discussion of Error:

During week 1, we performed the solubility test which resulted in us believing that the unknown compound was either semi-soluble or non-soluble. However, once we performed the flame test and the carbonate test we concluded that the compound contained both a carbonate and Sodium.

Evidence:

pH test: litmus paper test. Both the unknown and the provided substance was observed to be blue.

Flame test: wooden sticks were soaked in the solutions created from the solubility test then placed into a flame

Carbonate test: 1mL of both solutions created from the solubility test were placed in separate test tubes and a few drops of 3M HCl and observed fizzing or a small bubble.

Reasoning:

pH Test: Both papers tested for the different solutions had equal amounts of ions.

Flame Test: Both sticks had the same flame color which showed that they contained the same cations

Carbonate Test: both test tubes fizzed when 3M of HCl was added which showed that they contained the same anions.

References:

 â€œDealing With Unknowns.” LabArchives, Your Electronic Lab Notebook, mynotebook.labarchives.com/.

Libretexts. “Flame Tests.” Chemistry LibreTexts, Libretexts, 21 Aug. 2018, chem.libretexts.org/Textbook_Maps/Inorganic_Chemistry/Supplemental_Modules_(Inorganic_Chemistry)/Descriptive_Chemistry/Elements_Organized_by_Block/1_s-Block_Elements/Group__1:_The_Alkali_Metals/2Reactions_of_the_Group_1_Elements/Flame_Tests.

SODIUM CARBONATE ANHYDROUS, www.atmos.umd.edu/~russ/MSDS/sodium_carbonate_anhydrous.htm.

 â€œWeek 1 - Data and Notes.” LabArchives, Your Electronic Lab Notebook, mynotebook.labarchives.com/.

 â€œWeek 2 - Data and Notes.” LabArchives, Your Electronic Lab Notebook, mynotebook.labarchives.com/.

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