Determining The Properties Of Acids And Bases Lab Report
Determining the Properties of Different Acids and Bases
Yamin Liu
November 16th, 2017
Chemistry 1021
Section: 427
Benton Smith
Discussion of Results
The goals of this experiment were to find the identities of four unknown compounds and to first determine the pH. We then were required to run a series of anion and cation tests to determine the composition of the unknown solutions. To get more knowledge about these solutions we ran a series of dilutions to see if anything changed. Finally we tested the pH of household items and ran titration experiments with them to have a better look at environmental impact for safe disposal.
When we received the four different samples they were labeled as A6, B6, C6 and …show more content…
D6. There was a list on the board of the different possible solutions they could be, so the first step we took was to test the pH of the different solutions to determine which were acidic or basic. Using litmus paper and a basic pH key in the lab we determined that A and C were acidic while B and D were the bases. We then used a pH probe to achieve a more accurate reading just in case. We began to start the anion tests to determine the composition of each and we started first with the chloride test. This required us to add 1ml of each unknown to a test tube with 1ml of 6M HNO3 and 1ml of AgNO3 and a white precipitate would form in the presence of the chloride ion. The unknown A and C were both positive for this test which made more sense because HCL was one of the choices on the board and the pH of unknown solution A was a reading of 1 so we had a good idea that was going to be its identity based on the given choices. We then moved on to the next test for the sulfate ion in which we placed 1ml of the unknown in the test tube then added 1ml of 6M HCl and 1ml of BaCl2. There was no formation of a white precipitate so this indicated the unknowns remaining tested negative for this and we moved to the nitrate test. This one involved many careful steps to ensure an accurate experiment. 3ml of concentrated H2SO4 was carefully added to 1ml of the unknown in a test tube and mixed thoroughly. After the mixture cooled we tilted the tube to a 45degree angle and carefully poured 2ml of FeSO4 so it would float on top of the heavier liquid. Unfortunately there was not a brown ring appearing and this test was also negative for both. The last anion test was for acetate where we placed 2ml of the unknown in a test tube and added 1 drop of concentrated sulfuric acid. We then added 1ml of ethanol and heated the solution for a few minutes in a hot water bath on the hot plate. The unknown D tested positive for this in which it produces a unique fruity smell so we confirmed the anion of this solution. Unknown solution B tested negative for every anion test and this created confusion because it was hard to determine the identity without knowing the anion present. We continued with the cation tests to determine the others and maybe get help with identifying B.
There were two experiments we could run for testing the cations, one was the ammonium test and the other was a basic flame test. We heated a wire loop first then dipped it in the individual samples to place in the flame and record the color of the flame emitted. When testing A it was hard to tell a difference and we determined it was unknown based on this because of no change. After looking over the properties of the given choices HCl was the only strong acid that had the chloride anion so we determined this had to be the identity. During the test for B the flame had a very faint purplish/violet color hue to it and we made sure by testing a few more times to confirm. This proved the presence of the potassium cation and by looking over the given choices we identified this unknown as potassium hydroxide. Since the solution proved negative for our anion tests and the hydroxide would not have shown up on any of those tested. We had another problem with C when we could not observe a noticeable color change so we decided to run the ammonium test with this unknown. We placed 1ml of solution B in a test tube with 1ml of 6M NaOH and we were to waft the air above the mixture. The resulting solution had a definite smell of ammonium, which determined this unknown’s identity as ammonium chloride. Finally we ran a flame test on the unknown C solution and this experiment proved a definite positive result for sodium. The color the flame produced was a vibrant orange that was unmistakable so we identified this solution as Sodium acetate. The results for the anion and cation tests can be seen below in Table 1 and Table 2.
To reach a better understanding of these solutions we ran a series of dilutions we majorly dilute them down from 1M to .0001M. We used 1ml of the solution and added it to 9ml of water making the concentration .1M and then recorded the pH. We then took 1ml of the mixed solution and diluted it with another 9ml of water to a concentration of .01M and recorded the pH again. We ran these dilutions the same as the previous ways until the final concentration in the last tube was .0001M and we could see the change in the recorded pH. We used the pH probe to achieve an exact reading and we needed to be more precise than whole numbers. The acids pH increased while the bases pH decreased. We did notice that the strong acid and the strong base had a bigger jump in numbers with a pH difference of about ~4 while the weak acid and base had a pH difference of about ~2 or less. These pH recordings can be seen in Table 3. Based on the results the weak acid and base would be better for environmental impact as they were closer to being neutral and had much lower concentrations as shown in Table 5.
The final experiments we did were with household chemicals and we recorded the pH and performed titrations to analyze the different concentrations.
We used 70% and 91% isopropyl alcohol, pinesol and Windex as our chemicals and recorded their pH using a pH probe as shown in Table 4. Both isopropyl alcohols were very close to being neutral while the Windex was very basic and the pinesol was very acidic. The titrations showed the concentrations and these can be seen in Table 5, they were all very low but the 70% isopropyl was extremely low showing this is great for environmental impact disposal and it being an organic …show more content…
compound.
We had a few problems with this experiment that involved a problem in the titration of unknown solution D and trouble identifying B. During the titration of D the pH probe was shaking around in the beaker causing the graph to be very sporadic but this did not interfere with the final results but we reran the experiment just in case. In finding the identity of B we ran the anion tests twice because we figured there was a mistake in one of them causing them all to come out negative. After running each test again we received the same results from each so we knew it couldn’t have one of those ions present in solution.
Scientific Explanation
During the first step of this experiment we found the pH of the unknown solutions with litmus paper and placing a strip in the desired solution and then waiting for a color change.
This happens because the strip is stained with litmus, which changes color to indicate the acidity or alkalinity of a solution. In chemistry acids are known to be proton donors while bases are proton acceptors1. Unknown B had a pH of 13.77, which is a very high base, and this is because the cation potassium is an alkali metal having very low ionization enthalpy. Unknown A was identified as HCl, which had an initial pH of 0.56, and this is a well-known strong acid. HCl ionizes completely in water unlike other weak acids that partially ionize3. During the tests for the anions present in the unknown solutions we learned a lot about our solutions. For the first test, chloride anion, we received positive results from A and C. This is because they had chloride anions present and when mixed with AgNO3 and HNO3 the chloride ion solutions are used because silver nitrate is insoluble in HNO3. During the acetate anion test we had a positive result for solution D that proved the presence of the acetate ion. This reaction was from one drop of concentrated sulfuric acid and 1ml of ethanol and then required heating to excite the solution. Since ethyl acetate was produced we knew D contained the acetate anion, the fruity aroma produced after the solution was heated to release a gas proved this. This newly made
ethyl acetate is considered an ester, which has weak intermolecular forces producing a smell2.
The next step involving the cations tests we started with the flame test, which was the fastest. This flame test determines the cation present by producing a special color when a drop of solution is heated over a Bunsen burner. Each flame color corresponds to the chart of elements and their own color and intensity. Each element on the table has its specific color according to its line emission spectrum. This happens by exciting the electron present and moving it to a higher energy level where it emits its specific color then goes back to its regular state. The color emitted is according to its energy level, potassium burned a purple/violet color while the sodium burned a bright orange/yellow and this is because the wavelength for the sodium is at a higher level than potassium.
Table 1
Unknown Chloride Sulfate Nitrate Acetate Result
A6 Positive; formation of solid white precipitate (AgCl). Negative Negative Negative Chloride
B6 Negative Negative Negative Negative Unknown
C6 Positive; formation of solid white precipitate (AgCl). Negative Negative Negative Chloride
D6 Negative Negative Negative Positive; production of fruity smell. Acetate
Table 2
Unknown Solution Flame Test Ammonium (NH4 ) Test Results
A6 No color change Negative Unknown
B6 Pale violet color produced Negative Potassium
C6 No color change Positive Ammonium
D6 Bright orange color produced Negative Sodium
Table 3
Chemical Initial pH (1M) .1M pH .01M pH .001M pH .0001M pH
A6 0.56 1.67 2.99 3.90 4.70
B6 13.77 12.02 11.36 10.58 9.60
C6 5.98 6.60 7.11 7.40 8.01
D6 8.1 7.93 7.70 7.41 7.28
Table 4
Solution pH using probe
70% rubbing alcohol 7.58pH
91% rubbing alcohol 7.40pH
Pinesol 2.61pH
Windex 11.11pH
Table 5
Samples and Products Equation Concentration
A6 {x}{5mL}={.95M}{3.42mL} .6498M
B6 {x}{5mL}={1.05M}{4.10mL} .8610M
C6 {x}{5mL}={.95M}{.02mL} .0038M
D6 {x}{5mL}={1.05M}{.01mL} .0021M
70% Alcohol {x}{5mL}={1.05M}{.04mL} .0084M
Windex {x}{5mL}={1.05M}{.18mL} .0378M
Pine-Sol {x}{5mL}={.95M}{.84mL} .1596M
91% Alcohol {x}{5mL}={1.05M}{.16mL} .0336M
References
(1) Proton donors and acceptors http://www.chem1.com/acad/webtext/acid1/abcon-3.html (accessed Nov 15, 2017).
(2) Clark, J. an introduction to esters https://www.chemguide.co.uk/organicprops/esters/background.html (accessed Nov 15, 2017).
(3) Acid Strength http://www.mhhe.com/physsci/chemistry/chang7/esp/folder_structure/ac/m2/s1/acm2s1_1.htm (accessed Nov 16, 2017).
Yamin Liu
November 16th, 2017
Chemistry 1021
Section: 427
Benton Smith
Discussion of Results
The goals of this experiment were to find the identities of four unknown compounds and to first determine the pH. We then were required to run a series of anion and cation tests to determine the composition of the unknown solutions. To get more knowledge about these solutions we ran a series of dilutions to see if anything changed. Finally we tested the pH of household items and ran titration experiments with them to have a better look at environmental impact for safe disposal.
When we received the four different samples they were labeled as A6, B6, C6 and …show more content…
D6. There was a list on the board of the different possible solutions they could be, so the first step we took was to test the pH of the different solutions to determine which were acidic or basic. Using litmus paper and a basic pH key in the lab we determined that A and C were acidic while B and D were the bases. We then used a pH probe to achieve a more accurate reading just in case. We began to start the anion tests to determine the composition of each and we started first with the chloride test. This required us to add 1ml of each unknown to a test tube with 1ml of 6M HNO3 and 1ml of AgNO3 and a white precipitate would form in the presence of the chloride ion. The unknown A and C were both positive for this test which made more sense because HCL was one of the choices on the board and the pH of unknown solution A was a reading of 1 so we had a good idea that was going to be its identity based on the given choices. We then moved on to the next test for the sulfate ion in which we placed 1ml of the unknown in the test tube then added 1ml of 6M HCl and 1ml of BaCl2. There was no formation of a white precipitate so this indicated the unknowns remaining tested negative for this and we moved to the nitrate test. This one involved many careful steps to ensure an accurate experiment. 3ml of concentrated H2SO4 was carefully added to 1ml of the unknown in a test tube and mixed thoroughly. After the mixture cooled we tilted the tube to a 45degree angle and carefully poured 2ml of FeSO4 so it would float on top of the heavier liquid. Unfortunately there was not a brown ring appearing and this test was also negative for both. The last anion test was for acetate where we placed 2ml of the unknown in a test tube and added 1 drop of concentrated sulfuric acid. We then added 1ml of ethanol and heated the solution for a few minutes in a hot water bath on the hot plate. The unknown D tested positive for this in which it produces a unique fruity smell so we confirmed the anion of this solution. Unknown solution B tested negative for every anion test and this created confusion because it was hard to determine the identity without knowing the anion present. We continued with the cation tests to determine the others and maybe get help with identifying B.
There were two experiments we could run for testing the cations, one was the ammonium test and the other was a basic flame test. We heated a wire loop first then dipped it in the individual samples to place in the flame and record the color of the flame emitted. When testing A it was hard to tell a difference and we determined it was unknown based on this because of no change. After looking over the properties of the given choices HCl was the only strong acid that had the chloride anion so we determined this had to be the identity. During the test for B the flame had a very faint purplish/violet color hue to it and we made sure by testing a few more times to confirm. This proved the presence of the potassium cation and by looking over the given choices we identified this unknown as potassium hydroxide. Since the solution proved negative for our anion tests and the hydroxide would not have shown up on any of those tested. We had another problem with C when we could not observe a noticeable color change so we decided to run the ammonium test with this unknown. We placed 1ml of solution B in a test tube with 1ml of 6M NaOH and we were to waft the air above the mixture. The resulting solution had a definite smell of ammonium, which determined this unknown’s identity as ammonium chloride. Finally we ran a flame test on the unknown C solution and this experiment proved a definite positive result for sodium. The color the flame produced was a vibrant orange that was unmistakable so we identified this solution as Sodium acetate. The results for the anion and cation tests can be seen below in Table 1 and Table 2.
To reach a better understanding of these solutions we ran a series of dilutions we majorly dilute them down from 1M to .0001M. We used 1ml of the solution and added it to 9ml of water making the concentration .1M and then recorded the pH. We then took 1ml of the mixed solution and diluted it with another 9ml of water to a concentration of .01M and recorded the pH again. We ran these dilutions the same as the previous ways until the final concentration in the last tube was .0001M and we could see the change in the recorded pH. We used the pH probe to achieve an exact reading and we needed to be more precise than whole numbers. The acids pH increased while the bases pH decreased. We did notice that the strong acid and the strong base had a bigger jump in numbers with a pH difference of about ~4 while the weak acid and base had a pH difference of about ~2 or less. These pH recordings can be seen in Table 3. Based on the results the weak acid and base would be better for environmental impact as they were closer to being neutral and had much lower concentrations as shown in Table 5.
The final experiments we did were with household chemicals and we recorded the pH and performed titrations to analyze the different concentrations.
We used 70% and 91% isopropyl alcohol, pinesol and Windex as our chemicals and recorded their pH using a pH probe as shown in Table 4. Both isopropyl alcohols were very close to being neutral while the Windex was very basic and the pinesol was very acidic. The titrations showed the concentrations and these can be seen in Table 5, they were all very low but the 70% isopropyl was extremely low showing this is great for environmental impact disposal and it being an organic …show more content…
compound.
We had a few problems with this experiment that involved a problem in the titration of unknown solution D and trouble identifying B. During the titration of D the pH probe was shaking around in the beaker causing the graph to be very sporadic but this did not interfere with the final results but we reran the experiment just in case. In finding the identity of B we ran the anion tests twice because we figured there was a mistake in one of them causing them all to come out negative. After running each test again we received the same results from each so we knew it couldn’t have one of those ions present in solution.
Scientific Explanation
During the first step of this experiment we found the pH of the unknown solutions with litmus paper and placing a strip in the desired solution and then waiting for a color change.
This happens because the strip is stained with litmus, which changes color to indicate the acidity or alkalinity of a solution. In chemistry acids are known to be proton donors while bases are proton acceptors1. Unknown B had a pH of 13.77, which is a very high base, and this is because the cation potassium is an alkali metal having very low ionization enthalpy. Unknown A was identified as HCl, which had an initial pH of 0.56, and this is a well-known strong acid. HCl ionizes completely in water unlike other weak acids that partially ionize3. During the tests for the anions present in the unknown solutions we learned a lot about our solutions. For the first test, chloride anion, we received positive results from A and C. This is because they had chloride anions present and when mixed with AgNO3 and HNO3 the chloride ion solutions are used because silver nitrate is insoluble in HNO3. During the acetate anion test we had a positive result for solution D that proved the presence of the acetate ion. This reaction was from one drop of concentrated sulfuric acid and 1ml of ethanol and then required heating to excite the solution. Since ethyl acetate was produced we knew D contained the acetate anion, the fruity aroma produced after the solution was heated to release a gas proved this. This newly made
ethyl acetate is considered an ester, which has weak intermolecular forces producing a smell2.
The next step involving the cations tests we started with the flame test, which was the fastest. This flame test determines the cation present by producing a special color when a drop of solution is heated over a Bunsen burner. Each flame color corresponds to the chart of elements and their own color and intensity. Each element on the table has its specific color according to its line emission spectrum. This happens by exciting the electron present and moving it to a higher energy level where it emits its specific color then goes back to its regular state. The color emitted is according to its energy level, potassium burned a purple/violet color while the sodium burned a bright orange/yellow and this is because the wavelength for the sodium is at a higher level than potassium.
Table 1
Unknown Chloride Sulfate Nitrate Acetate Result
A6 Positive; formation of solid white precipitate (AgCl). Negative Negative Negative Chloride
B6 Negative Negative Negative Negative Unknown
C6 Positive; formation of solid white precipitate (AgCl). Negative Negative Negative Chloride
D6 Negative Negative Negative Positive; production of fruity smell. Acetate
Table 2
Unknown Solution Flame Test Ammonium (NH4 ) Test Results
A6 No color change Negative Unknown
B6 Pale violet color produced Negative Potassium
C6 No color change Positive Ammonium
D6 Bright orange color produced Negative Sodium
Table 3
Chemical Initial pH (1M) .1M pH .01M pH .001M pH .0001M pH
A6 0.56 1.67 2.99 3.90 4.70
B6 13.77 12.02 11.36 10.58 9.60
C6 5.98 6.60 7.11 7.40 8.01
D6 8.1 7.93 7.70 7.41 7.28
Table 4
Solution pH using probe
70% rubbing alcohol 7.58pH
91% rubbing alcohol 7.40pH
Pinesol 2.61pH
Windex 11.11pH
Table 5
Samples and Products Equation Concentration
A6 {x}{5mL}={.95M}{3.42mL} .6498M
B6 {x}{5mL}={1.05M}{4.10mL} .8610M
C6 {x}{5mL}={.95M}{.02mL} .0038M
D6 {x}{5mL}={1.05M}{.01mL} .0021M
70% Alcohol {x}{5mL}={1.05M}{.04mL} .0084M
Windex {x}{5mL}={1.05M}{.18mL} .0378M
Pine-Sol {x}{5mL}={.95M}{.84mL} .1596M
91% Alcohol {x}{5mL}={1.05M}{.16mL} .0336M
References
(1) Proton donors and acceptors http://www.chem1.com/acad/webtext/acid1/abcon-3.html (accessed Nov 15, 2017).
(2) Clark, J. an introduction to esters https://www.chemguide.co.uk/organicprops/esters/background.html (accessed Nov 15, 2017).
(3) Acid Strength http://www.mhhe.com/physsci/chemistry/chang7/esp/folder_structure/ac/m2/s1/acm2s1_1.htm (accessed Nov 16, 2017).