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Development of an Equation Essay

Purpose: Investigate a chemical reaction using lab procedures and observations. Then, find a pattern of reactivity and explain the findings using a chemical equation and particle diagram. Procedure: Refer to: Department of Chemistry, The Ohio State University. “Development of an Equation.” General Chemistry 1210 Laboratory Manual. Vol. 2013-2014. Plymouth: Hayden-McNeil. 32-35. Data/Results:

Part A: In the potassium iodide solution, I think there were potassium atoms as well as iodine atoms. In the lead nitrate solution, I think there were lead and nitrate ions. The potassium atoms and the lead atoms can be classified as cations, since they are metals. The iodine atoms and the nitrate ion can be classified as anions since they are nonmetals. Upon mixing, the solution turned into a cloudy yellow color. Evidence that a chemical reaction occurred was that the two solutions created a new color because the two solutions were originally colorless. There was no gas formed. Part B:

(Testing the Anions)
Iodide reaction with hydrogen peroxide observations- The precipitate at the bottom turned into a red solid and the liquid solution was a dirty yellow color. Nitrate reaction with hydrogen peroxide observations- A colorless precipitate formed at the bottom and looked like a bubble. It was a relatively large bubble. The liquid solution was colorless and cloudy/fizzy. Since the reaction resulted in some fizzing and bubbles, this is indication that a gas was formed. (Testing the Cations)

Potassium reaction with thioacetamide observations – No reaction occurred. Lead reaction with thioacetamide observations – A violet-black precipitate formed at the bottom of the test tube and the liquid solution was a cloudy grey color. It was about the same size precipitate as the nitrate reaction with hydrogen peroxide. Strong smell from the thioacetamide.

Part C: Identification of ions in the precipitate that forms when lead nitrate solution is added to potassium iodide solution. (Testing for Anions)
Reaction with hydrogen peroxide observations- A dark red precipitate formed at the bottom of the test tube and the liquid solution was colorless. There was not a large amount of precipitate formed and it sort of smeared along the inside of the test tube. Inferences: What anions are in the precipitate? -iodine (I-) When compared with results from part B to test anions, similar results were found. A dark red precipitate was formed in both.

(Testing for cations)
Reaction with hydrogen sulfide observations- A small, violet-black precipitate formed at the bottom of the test tube and the liquid solution was grey and cloudy. Inferences: What cations are in the precipitate? – lead (Pb2+) When compared with results from part B to test cations, similar results were found, A violet-black precipitate was formed in both tests. Exchange reaction- Positive potassium started off with negative iodine, and positive lead started off with negative nitrate. Potassium switched to combine with nitrate and lead switched to combine with iodine. Part D:

Testing of Precipitate| Observations on Initial Precipitate Formed (relative amount, etc.)| Lead Nitrate: Potassium Iodide Ratio| Tube 1| Powdery, yellow precipitate formed at the bottom. Not very much precipitate. Little to no streaking. Clear liquid solution above precipitate. | 3:1| Tube 2| Powdery, yellow precipitate formed at the bottom. Equal to tube 1. Little to no streaking. Clear liquid solution above precipitate.| 2:1| Tube 3| Powdery, yellow precipitate formed at the bottom. A little more precipitate than tube 1 and 2. Little to no streaking. Clear liquid solution above precipitate.| 1:1| Tube 4| Powdery, yellow precipitate formed at the bottom. Much more than tube 3. Noticeable streaking of precipitate along sides of test tube. Clear liquid solution above precipitate.| 1:2| Tube 5| Powdery, yellow precipitate formed at the bottom. Most precipitate formed out of all test tubes. A lot of streaking of the precipitate along sides of the test tube. Clear liquid solution above precipitate. | 1:3|

Testing of Supernatant| Observations| Inferences: Which ions were in the supernatant? List cations and anions.| Tube 1| The solution was clear with lead nitrate, but turned a yellow cloudy color with the potassium iodide. | Pb2+ (lead)-cationsNO3- (nitrate)-anions| Tube 2| The solution was clear with lead nitrate, but turned a yellow cloudy color with the potassium iodide.| Pb2+ (lead)-cationsNO3- (nitrate)-anions| Tube 3| The solution was clear with lead nitrate, but turned a yellow cloudy color with the potassium iodide.| Pb2+ (lead)-cationsNO3- (nitrate)-anions| Tube 4| The solution was clear with both the lead nitrate and the potassium iodide.| Pb2+ (lead)-cationsNO3- (nitrate)-anions| Tube 5| The solution was a little yellow with the lead nitrate, and a little less yellow with the potassium iodide.| K+ (potassium)I- (iodine)|

Discussion/Conclusion: In part A, the first step was to obtain 5 drops of potassium iodine and 5 drops of lead nitrate and put them into a test tube and record observations. Then, to test the anions in part B, 5 drops of potassium iodine, 5 drops of nitric, 10 drops of dichloroethane, and 5 drops hydrogen peroxide to a new test tube. Then to a separate test tube, 5 drops of potassium nitrate, 5 drops of nitric acid, 10 drops of dichloroethane, and 5 hydrogen peroxide to a new test tube. Both should be stoppered and shook to produce two distinct layers. To test the cations, 2 test tubes would each get 20 drops of thioacetamide and 2 drops of nitric acid. One would get 5 drops of lead nitrate and the other 5 drops of potassium nitrite. Both test tubes were heated for 5 minutes and observations were recorded. In part C, the sample was used from part A and the test tube was centrifuged, then the clear aqueous layer was removed and discarded and the precipitate was washed with distilled water. This process was repeated once more. To test the anions, 5 drops of nitric acid, 10 drops of dichloroethane, and 5 drops of hydrogen peroxide were added to the solid precipitate and the test tube was stoppered and shook.

These results were compared to the results from part B. To test for cations, the less colored aqueous layer was transferred to a clean test tube and the leftover layer was discarded. The solution was heated in a water bath until clear. 20 drops of thioacetamide were added, stirred then heated in a water bath and compared to the results from part B. In part D, to determine the ratio of ions in the precipitate, 5 test tubes were labelled 1-5 and were filled according to table 3.1 on page 34 of the lab manual. The same medicine dropper was used for all drops and the test tubes were stoppered and shook, then centrifuged. The relative amounts and appearance of each precipitate were recorded. To test for potassium of iodide ions in the supernatant, 5 drops of lead nitrate were added to 5 separate test tubes with along with 5 drops from the appropriate test tube solution. The same was done to test for lead or nitrate ions, but potassium iodide was added instead. The perfect ratio for this lab was 2 potassium iodides for every lead nitrate. This ratio was found from balancing the equation and from comparing the results from part C to part B to match the observations of the precipitates.

The ratio is the molar mass ratio of the balanced equation. The balanced equation was: 2KI(aq)+Pb(NO3)2(aq) 2KNO3(aq)+PbI2(s) and the formula of the precipitate was PbI2(s) based on the observations. In part B, the test for anions resulted in a dark red precipitate which was the iodide solution with hydrogen peroxide. In part C, the same results were found when lead nitrate and potassium iodide were added to hydrogen peroxide, therefore; the anions found were iodide ions because it has a negative 1 charge. In part B to test cations, the precipitate was a violet-black color for the lead solution reaction with thioacetamide. In part C, the same results were found when lead nitrate and potassium iodide were added to hydrogen sulfide.

The cations found were lead ions since they have a positive 2 charge. Some inherent errors could have been while extracting the clear aqueous solution, some of the precipitate could have been extracted with the solution and transferred into another test tube. Upon heating, not all of the precipitate dissolved. Some of the drops with the micropipet varied also. The medicine dropper was more precise with the drops. Through this lab, a chemical reaction was used to find the pattern of reactivity which was an exchange reaction. This is known by finding the chemical equation and properly balancing it which is seen above. This lead to the ability to create a particle diagram and the findings of a perfect ratio of lead nitrate to potassium iodide.


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