Development of an Equation
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: HaydenMcNeil.
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.