Identification of Unlabeled Acidic and Basic Solutions through Analytical Testing

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Project Objective

For Project 7 unlabeled bottles of acids and bases needed to be identified. For week one we were assigned three unlabeled solutions. Before we can dispose the bottles or use them, we need to investigate their properties so that we can dispose them properly or reuse the acids and bases. To identify their properties a series of test like the cation and anion test were performed. Then titrations of unknown solutions were performed to identify them as either an acid or base.

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Week two unlabeled solutions were tested for their concentration/ph. Lastly week three we found household items that are acidic or basic and use different experiments to investigate their properties and concentrations.

Analytical Methods Employed

Cation and Anion Tests

When presented with unknowns, we first tested for the cation and anions, that could be present. Five tests were used to determine the chemical makeup of the compound. These tests are the Chloride, Nitrate, Carbonate, Acetate, and flame test.

These tests were the Chloride, Nitrate, Carbonate, and Acetate test. The Chloride test mixed 1 mL of the unknown with 0.1M Silver nitrate. The positive result for the test shows white precipitate. The Nitrate test uses 1 mL of unknown in a test tube and carefully adds 3 mL of sulfuric acid and 2 mL of iron sulfate. The positive result for the test shows a brown ring in the test tube.

The Carbonate test uses 1 mL of unknown solution in a test tube and adds 6 M HCL drop by drop. The positive result shows the solution effervesce.

The Acetate test places 2 mL of the unknown solution adds 1 drop of concentrated sulfuric acid, and then adds 1 mL of ethanol that will then be heated in a water bath. The positive result is indicated by a fruity smell of ethyl acetate. And lastly the flame test uses the technique of vaporizing a sample and noting the color imparted to the flame. As it pertained to the topic of the lab, these tests were important. A pH test could identify if the compound was an acid or a base, and while in our lab that might be enough, figuring out the specific makeup of the compound would be necessary for safe disposal in other settings.

Indicator vs PH Probe

Through these tests we observed the strengths and weaknesses between an indicator and a pH probe. The indicator was able to answer if the chemical was a base or acid, with little room for error of subjectivity, however this is all it was able to do. An indicator is unable to determine if the acid is weak or strong (without subjectivity), and between levels of the pH scale, the color is open to be interpreted different by different people, even with a color guide. While an indicator is easier to use, a pH probe is more effective because it can determine the pH with a numerical value, which makes it easier to interpret by the user, and can help classify it as weak or strong. In a test the indicator could return a color of red, red could be interpreted as a pH of one, two, or three. With a probe however, it can be determined that the pH was closer to 3 than it was to 1, a classification that would’ve swayed results drastically had a probe not been used.

However, the probe is not without fault. Firstly, it is more prone to human error than the indicator. For instance, by not properly cleaning the equipment, you could add some of the previous solution to the one currently being measured which could sway results. This change would be unnoticeable to the user as in most cases no physical change would occur unlike with an indicator where the paper may change color. For the context of the experiment the pH probe is the preferred measuring tool, due to its accuracy in measurement.

Weak vs Strong Acid and Bases

“An acid is a solution that produces H+ ions when it reacts when it is in an aqueous solution” (Study.com), the classification for said acid being weak or strong comes from the pH of the acid. Typically, strong acids have a pH between 0-2 with weak acids ranging from 2-7. Weak acids also tend to have observable physical properties that can help distinguish them such as smell, touch and taste (study.com). While still acidic, weak acids tend to have lower concentrations, making them less corrosive and dangerous, substances like lemon juice and sodas are consumable despite being acidic. With the data collected, the classification of the two acids, Unknown A and C can be determined.

Unknown A had a final concentration of 0.976M, as well as an initial pH of 1. This would hint at it being a strong acid, it passed multiple tests making it hard to identify. Unknown C also had an initial pH of 1, it had a relatively low concentration of 0.488M. A strong base is a fully ionic compound like a hydroxide reacting with a metal. While weak bases often have water as a byproduct of the reaction, are the pH is lower relatively because of the equilibrium constant, as defined by Le Chatelier's principle.

Conjugate Acids -Base Pairs

Conjugate Acid-base pairs are bases with an adjacent acid that share an H+ ion. “A conjugate acid contains one more H atom and one more + charge than the base that formed it. A conjugate base contains one less H atom and one more - charge than the acid that formed it” (Socratic). When the unknowns were tested, they carried properties from multiple anions. From the pH we could determine if they were acidic or not, and even conclude that they were strong acids. Unknown A passed every test but the carbonate test. Acetate and Nitrate are present as well as Sodium. It can infer that the acidic pair is HNO3, with the Acetate coming as byproduct of the reaction taking place with the solute. For all three solutions it is probable that the although each unknown passed multiple tests, this comes from the result of external reactions between the original solutions and the solution it was diluted in.

Experimental Findings

Table 1: Cation and Anion Test Results

Test Type	Unknown A	Unknown C	Unknown D
Chloride	Present	Absent	Present
Nitrate	Present	Absent	Absent
Carbonate	Absent	Absent	Absent
Acetate	Present	Present	Present
Flame Color	Sodium	Sodium	Sodium

Table 2: Solution Concentration and pH Analysis

Unknown Solution	Concentration (M)	Initial pH	Classification
A	0.976	1	Strong Acid
C	0.488	1	Strong Acid
D	0.571	11	Strong Base

Household Items pH Analysis

Table 3: Household Items - Acidic or Basic Properties

Item	Titration 1 pH	Titration 2 pH	Titration 3 pH
Lemon Juice	1	3	3
Gatorade	3	4	4
Sprite	5	4	3

Conclusion

After the tests involving the unknown compounds, unknown A contained chloride, acetate, nitrate, and sodium. Unknown C contained sodium and acetate ions. Unknown D contained chloride, sodium, and acetate ions. Along with containing the most ions, unknown A also had the largest density (concentration) while unknown C had the smallest density with the lowest number of ions through the test that were carried out. Through titration it was found the both unknown A and C had a pH of 1 (strong acid) while unknown D recorded a pH of 11 (strong base). Three household items were also tested using pH strips and were titrated to find the relationship between concentration and pH. Lemon juice recorded an initial pH of 1 and increased to 3 as concentration was increased. Gatorade recorded an initial pH of 3 and rose to 4 as concentration was increased. Sprite recorded an initial pH of 5 and was lowered to 4 through the last two titrations.