03 Madison Kothari

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University of Houston, Clear Lake *

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CHEM-131

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Chemistry

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Feb 20, 2024

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CHEM1112- section# Experiment #3 Your Name Date Qualitative Analysis of Anions Lab Partner: Lab Partner’s Name Procedure (3 pts) First obtain 9 test tubes with labels. Add the solution (known or unknown) to one of the test tubes and then add acetic acid till the solution is acidic. Add .1 M AgNO3 to the solution and then put in the centrifuge and pour off supernatant liquid. After wash the precipitate with distilled water and centrifuge again pour off water. Add NH3 to the precipitate in the test tube and centrifuge. Pour the supernatant liquid into test tube 3 and add 6M HNO3 if it’s not acidic add more HNO3. Discard contents in test tube. Add the solution (known or unknown) to test tube 4 add 6M HNO3 until acidic and .1 M Fe (NO3)3 and mineral oil. Shake the solution if the oil turns purple there are I- ions present. Take out the mineral oil with a dropper and add more, shake, and take it out again, repeat until the oil is clear. Add KMnO4 to test tube 4 until the solution is pink. Add mineral oil cover and shake the liquid. If the mineral oil is brown, there are Br- ions present. Add the solution (known or unknown) to test tube 6 as well as 6M HNO3 then place in a hot water bath. If/ when bubbles form transfer to a test tube with Ba (OH)2 if a white cloudy precipitate forms there is CO3 2- present. Add the solution (known or unknown) to test tube 7 add acetic acid until acidic then add .1 M BaCl2 if a white precipitate forms SO2- is present. Add the solution (known or unknown) to test tube 8 along with 6M NaOH until basic add aluminum granules to the test tube and put a small cotton ball about halfway down the tube where it’s not touching the liquid add a piece of pH paper above the cotton ball. Place the test tube in a hot water bath until the liquid starts forming bubbles if the pH paper changes colors to blue/ green then NH3 is present. Data and Observations (12 pts) (be mindful of units and significant figures) 1

CHEM1112- section# Experiment #3 Your Name Date Qualitative Analysis of Anions Lab Partner: Lab Partner’s Name Procedure Known Solution Unknown Solution Results Conclusions Results Conclusions Example) Add AgNO 3 to solution in Test Tube 2. Example) White precipitate forms. Example) Cl - , Br - or I - are present. White precipitate forms Cl-,Br- or I- are present Add HNO3 to test tube 3 White precipitate forms Cl- present nothing Cl- Not present Add Fe(NO3)3 to test tube 4 Mineral oil pink/purple I- Ions presen t Purple mineral oil I- Presen t Add KMnO4 to test tube 4 Mineral oil brown Br- present nothing Not present Add HNO3 to test tube 6 Bubbles form CO3 2- is present Bubbles formed CO3 2- present Add BaCl2 to test tube 7 Percipitate forms SO4 2- is present Percipitate forms SO4 2- present Add NaOH to test tube 8 pH paper turns green/ blue NO3- is present pH paper turned green NO3- is present U n k n o w n s o l u t i o n # _ Identified presence of the following anions: SO4 2-, NO 3-, I-, CO3 2- Identified absence of the following anions: Br- , Cl- 2

CHEM1112- section# Experiment #3 Your Name Date Qualitative Analysis of Anions Lab Partner: Lab Partner’s Name _ _ c _ _ Potential Error Sources One source of error that could have struck was that there could have been a reaction that we didn’t notice happen because it happened too quickly, and we didn’t catch it on our initial known solution so when we did the same test for the unknown, we may have seen something we didn’t see before or thought we saw something we didn’t see. Another source of error could have been when we took out parts of the supernatant liquid, we could have gotten some precipitant in it that could have potentially change our results. Post-Lab Questions (5 pts) 1) Write oxidaiotn and reduction half-reaction equations that describe the test for identifying NO 3 – (NO 3 is reduced to NH 3 (gas) witht the presence of Al). Oxidation: Al(s)+ OH- (aq) => Al(OH)- (aq)+ 3 e- Reduction NO3- + 6H2O+8e- => NH3 (g)+ 9 OH- (aq) 2) Explain why the test for I – must be done before testing for Br – . IF KMnO4 was used first it would have taken out the I- and Br- so we wouldn’t be able to know which one is in the solution. Fe(NO3)3 is only strogn enough to take out the I- while leaving the Br- behind 3) Which one of the iodine species dissolved in the mineral oil, and why ? I2 is dissolved because non-polar molecules dissolve other non-polar molecules. “like dissolves like” 1. Iodine 2. Iodide 3

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