Identification of an Unknown Chemical Substance

Introduction

Identifying unknown chemicals in everyday life includes analyzing different types of substances and the compounds that form them. This is essential in chemistry as scientists are constantly trying to find out the basis of substances which allow them to use those in chemical reactions to form new chemical substances and medicines. Figuring out chemicals and their properties in the lab also helps us discover and define them in real-life experiences. An example of this type of situation, where there is a need to identify chemicals, is drug and alcohol tests.

When being hired or becoming a part of the American army, and many other situations, it is essential to test to see if someone's behavior, abilities, and mind are being affected by the use of substances (legal and illegal) that can damage someone's proper judgment. Studies show that someone's performance and attitude are affected when they have substance abuse problems, that goes for licit and illicit drugs.

Theory

The tests done during the experiment to find out the unknown sample are gravimetric analysis, pH test, conductivity, flame test, and solubility.

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Gravimetric analysis is ideal for inorganic compounds that form precipitates, and it was suitable for the experiment based on the unknown sample identified by our group. The pH test was important for knowing whether the sample was acidic, basic, or more neutral, which in this case, the pH was more acidic. Solubility test in water was an important factor as it played a role for us in deciding what to react with the unknown sample once we had some idea about its identity; the unknown substance was not soluble in both samples; ethanol and acetone.

Conductivity tests helped us differentiate between whether the sample was a metal or nonmetal, as metals tend to be much better conductors of heat and electricity than nonmetals. Finally, the flame test provided qualitative data such as the color of the sample; the unknown compound had a strong orange/red color. All these tests were steps in solving for the unknown sample, as each played a significant role in giving more information about the sample.

Hypothesis

From the physical properties of the unknown sample, and the multiple tests executed by our group the hypothesis was that the unknown sample was Calcium Chloride, CaCl₂. It was a small colorless crystal, that was found to have an acidic pH, a red color when burned, that led us to form this hypothesis.

Objectives

This experiment has two objectives as it took place for two days.

Week 1 Objective: To determine inorganic contaminants present in water samples from different sources by using qualitative tests such as pH test, flame test, etc. The main purpose was to find out qualitative information crucial to identifying the unknown sample. In Week 1, our team made use of tests such as the ones mentioned above in addition to conductivity and solubility tests.

Week 2 Objective: To use quantitative and qualitative tests such as gravimetric analysis and flame test, to confirm our group's hypothesis, CaCl₂. Our unknown sample was such where gravimetric analysis was more suitable, and therefore, this method was used to verify the sample we had identified.

Methods

Part 1

1. Solubility test:
   • Take a small amount, about 0.5g of the unknown substance and mix it with 5 mL of ethanol in a volumetric flask.
   • Observe if the substance dissolves, if it does it means it soluble.
2. pH test:
   • First, measure the pH of water as a source of comparison.
   • Then take a pH strip, dip it into the solution, and record findings in the data table about pH level. Then repeat the step to make sure of the results.
3. Conductivity test:
   • Place the conductivity sensors into the beaker and turn on conductivity meter.
   • Record if the solution conducts electricity in the table. Repeat the step.
4. Flame test:
   • Take a wire loop and rinse it with deionized water, and take a bit of the unknown sample.
   • Turn on Bunsen burner and hold the coated metal wire into the flame.
   • Observe the change in color of the flame and record data into the table.
   • Repeat the above steps to verify data collection.
5. Analysis of ions:
   • After analyzing the data collected, decide whether to continue with gravimetric or volumetric analysis.
   • Figure out cations and anions that can be formed from the sample based on the solubility rules.

Part 2

• After figuring out the unknown sample, use gravimetric analysis if necessary.
• Gravimetric Analysis: Mix the solution with another aqueous solution that should create a precipitate based on solubility rules, using the assumption of the group for the unknown compound, use the gravimetric analysis to determine the precipitation.
• Use stoichiometry to estimate how much product we should get if we started with 0.5 grams of the unknown sample.

Safety and Materials

The materials used were general laboratory glassware such as beaker, test tubes, and volumetric flask pH strips, wire loop, conductivity tool, Bunsen burner, etc. Personal protective equipment (laboratory coat, goggles, and gloves) always should be properly used during the lab. Hands were washed properly at the end of the lab, and the rest of the chemicals used, and solutions left are not be poured down the drain, they were disposed of properly in the waste containers (solid, liquid waste). Small quantities of reactants were used as most qualitative tests are done in small test tubes.

• Calcium chloride, CaCl₂: can cause eye irritation and therefore, wear PPE and read the label before using it.
• Sodium nitrate, NaNO₃: may intensify fire.
• Ammonium sulfate, (NH₄)₂SO₄: can be harmful if swallowed, and therefore, do not eat or rinse it in the mouth.
• Ammonium chloride, NH₄Cl: can be harmful if swallowed.
• Magnesium sulfate, MgSO₄: should be kept out of reach of children, and the label needs to be read before using it. It also causes static electricity charges.
• Calcium nitrate, Ca(NO₃)₂: can cause damage to organs and intensify fire.
• Sodium chloride, NaCl: can cause respiratory tract irritation and should be used with adequate ventilation.
• Hydrogen chloride, HCl: can cause serious eye damage, and should not be let into contact with organics.
• Sodium hydroxide, NaOH: is corrosive to metals and can cause serious skin damage.

PPE should always be worn when using the mentioned chemicals, as it is the best way to stay safe. Other than that, it is safe to not touch any chemicals without gloves or smell them, as some can cause respiratory irritation.

Results

Part 1

Qualitative tests used:

Part 2: Calculations

Na₂CO₃ (aq) + CaCl₂ (aq) --> CaCO₃ (s) + 2Cl (aq)

Filter paper weight = 0.30 grams

Unknown mass = 0.56 grams – 0.30 grams = 0.26 grams

Known mass of CaCl₂ = 0.42 grams – 0.30 grams = 0.12 grams

0.12 grams of CaCl₂ * 1 mol CaCl₂/111.078 grams of CaCl₂ = 0.00108 moles of CaCl₂

0.00108 moles of CaCl₂ * 1 mole NaCO₃/ 1 mole CaCl₂ * 82.99 grams of NaCO₃/ 1 mole NaCO₃ = 0.0896 grams of NaCO₃

Percent yield= 0.12 grams/ 0.19 grams * 100% = 63%

Discussion

Part 1

In Part 1, the results confirmed that the compound was indeed an inorganic sample as it was soluble in water but insoluble in the organic solvents. The different tests used such as the flame test further facilitated the hypothesis that the sample was Calcium Chloride, the pH values did help confirm that hypothesis. The pH values for Calcium Chloride are usually acidic and between 5.5 and 6.5, the values found by our group confirmed that result. It was the Conductivity test where our team identified the small unknown substance as Calcium Chloride. Lastly, the flame test helped confirm the hypothesis, with a strong orange/red color when burned. The data does support our hypothesis, as Calcium Chloride is red/orange flame when burned, soluble in water but not organic solvents and has an acidic pH.

Part 2

In Part 2, we used gravimetric analysis because Calcium Chloride, CaCl₂, is a compound that forms precipitates when it is involved in chemical reactions. To test this theory, we used Sodium Carbonate, Na₂CO₃, and predicted that one of the products named Calcium Carbonate, CaCO₃, would be the precipitate in our reaction. We did the calculations and reported the expected mass of the precipitate that we would get if we had started the experiment with 0.54 grams of our unknown. This test was done to verify our identity of the unknown sample and to better understand how gravimetric analysis worked. The percent yield was 63%, so it showed that our data collection was not as accurate as it could be.

Sources of Error

Some major sources of error could be inaccurate measures of known compounds and water. Those could be eliminated or at least lessened with accurate measurement. However, by not doing so it could lead to having an incorrect identification of the unknown sample. There were not really any limitations of the equipment and processes used. Our team did several tests throughout Weeks 1 and 2 to find the unknown sample and used various equipment such as volumetric flask and Bunsen burner. The changes proposed would be paying extra attention to all the measurements taken and whether the molar ratios were the same, as they had to be during the experiment, making all the calculations correctly and proofreading the whole plan to avoid unnecessary steps that could lead to mistakes.

Conclusion

The purpose of the experiment was to determine the identity of an unknown sample given to the lab group by the TA. When we executed the experiment, we learned how to perform several tests which are required to find the identity of a compound. This experiment has solidified our skills in carrying out qualitative tests such as pH, flame, solubility, conductivity, and quantitative tests such as gravimetric analysis. We also learned many properties of different compounds that could help us identify a substance faster when asked to. We investigated the program through a trial and error process, which involved experimenting with different chemicals and making conclusions based on tests. In the end, our results were not fully perfect, but that is how scientific data works. The evidence of having a small colorless crystal was what supported our hypothesis that the unknown sample was Calcium Chloride, CaCl₂. As the researchers, we are intrigued by the importance of qualitative and quantitative tests in the world of chemistry. Being able to identify a compound through chemical methods was what we primarily learned from this project, and we hope this skill will continue to help us in future chemistry projects.

Research Connection

The article chosen focuses on the identification of benefits and damages energy drinks could cause to your health. Consumption of energy drinks has been increasing dramatically in the last two decades, particularly among teenagers and young adults. Energy drinks are claimed to improve physical and cognitive performance and offer an energy boost; however, the number of studies supporting this claim is limited. In fact, many health issues are related to the amount of chemicals and sugar used in this drink that raises the question of whether these beverages are safe. This article's goal was to identify and discuss beneficial and disadvantageous health effects related to energy drinks. Although energy drinks may have beneficial effects on physical performance, these products also have possible detrimental health consequences. Marketing of energy drinks should be limited or forbidden until independent research confirms their safety, particularly among adolescents.