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Mindy WeiChemistry 1411-026 (Group 6; Partners: Yazmine Tembunde, Jessica Wilburn)19 October 2015CSI: Unknown Compound LabIntroduction:

Unknown compounds can be found in situations in daily life such as pharmaceuticals,

environmental science, and police investigations. Identifying these unknowns could assist

scientists in finding cures for diseases, furthering environmental health, and discovering new

drugs being illegally distributed.1,2,3 Unknown compounds in pharmaceuticals can lead to

products with higher or lower toxicity, and therefore affect their effectiveness – they could

inhibit or induce enzyme processes and metabolize pathways in the human body that are

sensitive to environmental changes.1 Identification of compounds that contain compounds that

cause mutagens and act as possible carcinogens could prevent the environment from sustaining

the effects and upsetting balances in marine life and in the atmosphere.2 Denmark’s police

conducted an experiment analyzing the compounds found in trafficked synthetic drugs in 2008.3

Analysis of compounds can be conducted using tests available in a laboratory setting. Solubility

helps scientists determine the identity of a compound by using solubility rules, leaving a smaller

pool of possible compounds that can then be tested more specifically. Testing for the pH of a

compound dissolved in salt can give insight about the basicity or acidity and can be predicted

once it is dissolved in water. When the salt is a metal hydroxide as metal hydroxides usually

behave as bases, it will have a high pH value (>7 pH). Using pH paper and dipping it into a

solution of the compound and comparing the color of the pH paper to the color scale on the

container can confirm the pH of the salt solution. Upsetting pH balance can be related to cause of

mutagens in carcinogens in the environment, and therefore correcting the imbalance could solve

the environmental issues. Conductivity of a salt, which is dependent on the concentration of ions

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– and therefore has no standard value, is a result of its ability of the ions that make up the salt to

dissociate on a molecular level and can be used to help determine the identity of an unknown

compound. The conductivity of the unknown salt can be compared to the conductivity of a

known salt of the same concentration to compare their similarity and further the experiment to

conclude the identity of the unknown. Flame tests can be conducted to specifically determine the

cation of an unknown compound. As a solution of an unknown salt is placed in the flame, the

heat excites the electrons on the outermost electron shell and the electrons jump to a higher shell

– a chemical property, producing a specific flame color for each type of cation. Additional tests

that can be used to determine the identity of a unknown salt/compound are reacting insoluble

compounds with a strong acid such as hydrochloric acid or nitric acid and seeing if bubbles are

formed, and, in a lab with more extensive equipment, procedures such as chromatography and

mass spectrometry can be used to determine the identity of the compound. 3

Discussion:

The preliminary experiment led to the conclusion that the unknown compound was

calcium chloride (CaCO3) as it would not dissolve in water, but would dissolve in the presence of

a strong acid (HCl) and create bubbles of CO2. The second experiment required the synthesis of

the unknown compound with Na2CO3 and CaCl2 to produce CaCO3 and NaCl shown by the

reaction: Na2CO3 (aq) + CaCl2 (aq) 2NaCl (aq) + CaCO3 (s). The solid CaCO3 was then filtered

out with vacuum filtration and dried on a hot plate, and its purity tested by comparing the

conductivity of the synthesized compound to a lab compound. The percent yield of the

experiment was 101%, which can indicate the presence of impurities in the synthesized

compound due to lab errors and limitations.

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Limitations to the experiment included the difficulty of determining the color of the

flame when determining a cation. The test had to be repeated multiple times to confirm the

cation was calcium and some of the flames looked more orange than red. To better the results

and more specifically confirm the color of the flame, a spectrometer can be used to determine the

exact wavelength, if the equipment were available – giving the experiment better qualitative

data. Another limitation was the impurity of the vacuum filtration system, which caused

impurities to be filtered into the synthesized solid CaCO3 and caused the inaccurate percent

yield. To correct these results, sterilized lab equipment can be used to ensure no unwanted

material is filtered into the synthesized compound and upset the percent yield. Improper drying

could also have been a limitation to getting the correct percent yield as the heating was done on a

hot plate, and only carried out once. To better this limitation, the synthesized compound could be

dried multiple times until there was no mass change and therefore provide better qualitative data.

Future experiments could include the identification and synthesis of an insoluble

compound, which would then require more extensive testing such as using the silver nitrate tests

and barium chloride test along with the flame test and sodium hydroxide test to test for anions

and cations. This experiment did not require these tests due to the insoluble nature of CaCO3. It

was important to identify the compound using both physical properties (solubility) and chemical

properties (flame color) as it provided more extensive qualitative data. More than one compound

could have the same physical properties, but not the same chemical properties, and vice versa.

References:

1. Kosjek, T. Mass spectrometry for identifying pharmaceutical biotransformation products. TrAC Trends in Analytical Chemistry. Dec. 2007. Web. 19 Oct. 2015.

2. Le Lacheur, R. Identification of Compounds in Environmental Samples. Department of Environmental Sciences, UNC Chapel Hill. Dec. 1993. Web. 19 Oct. 2015.

3. Reitzel, L. Idetification of ten new designer drugs. Wiley Online. Nov 2011. Web. 19 Oct. 2015

On my honor as a student, I pledge that in have neither given nor received aid on this assignment.Mindy Wei