Finding the Formula for Lead Nitrate
This experiment was to test the different concentration levels of specified alkali metals to determine the greatest mass of lead nitrate.
III. Background Information:
Potassium Iodide is a crystallized, white salt but known to turn a bright yellow when exposed to prolonged moisture such as mixing with water. It is a simple iodine salt. In its natural state it is mostly colorless and odorless. If tasted, it would be like saline and extremely bitter and is has a relatively low level of hazard. Its main use is in photography but also used in table salt to “iodize” food and can be used in expectorants for lung congestion. It can also be used to protect the thyroid from radioactive iodine
Lead Nitrate is a hazardous colorless crystal or white powder. It has a long history of uses. Until 1974, when the dangers of lead were realized, it was in a variety of products.
White odourless solid
Decomposes at 290-470 ï¿½C
Solubility in water
52 g/100 ml (20 ï¿½C)
Solubility in nitric acid
1 g/2500 ml
1 g/75 ml
Dangerous for the environment (N)
R61, R20/22, R33,
S53, S45, S60, S61
* Electronic scale
* Lead Nitrate
* Potassium Iodide
* Graduated Cylinder
* Filter paper
1. Materials were gathered and then specific concentration ratio was received (water:solute 1:9)
2. Cylinder was filled with 100 milliliters of lead iodide
*Graduated Cylinder is hydrophobic
*Caution: Be sure of precise readings by measuring at the appropriate part of the miniscus
3. Cylinder was filled with 900 milliliters of KI
4. The solution was gently shaken to ensure even distribution of solute to solvent
5. Solution was then transferred to filter paper
*Two filter papers were used for double filtration
6. The filter paper was put into a funnel of a beaker to the solution would separate
a) mass of filter papers:
b) mass of lead iodide:
c) molar mass of KI: 165.998 g/mol
d) molar mass of Pb(NO2)3: 331.268 g/mol
e) calculation for determining molarity for each solution based on 1,000 ml:
200 ml/1000 ml x .5 ml = .1 ml
The two liquids started to both appear clear. After combined, it almost instantly turned to a neon yellow. While filtering, a colorless liquid seeped through while the yellow precipitate clung to the filter paper. There was little water in the flask but over half the filter paper had been covered in neon yellow.
One must ensure to
Read the meniscus at the proper point
Use a plastic graduated cylinder for elimination of meniscus
Measure by getting down at eye level
Carefully take proper measurements
Use two filter papers for double filtration
Zero the scale after first weighing the filter paper
Use an electronic scale for accuracy
Product enhancements to minimize error
Pipette’s measurements to allow a few drops of solution to be retained
Plastic graduated cylinders for no confusion
figure 1: rinsing setup
figure 2: Pipette dispensing of liquids
figure 3: filtering apparatus
The lab performed was found to be an effective way of discerning the formulation of lead nitrate and potassium iodide’s precipitate and use the chemical formula to understand the reaction. The formula is as follows: KI + Pb(NO3)2 –> PbI + K(NO3)2. Potassium Iodide and Lead Nitrate yield Lead Iodide and Potassium Nitrate. The reaction taking place is known to be a double replacement. The two compounds split and then combine with the counterparts. The PbI remains in the solution and the K(NO3)2 forms the precipitate. The purpose of the experiment was to find which combination of concentrations would consequently have the greatest impact on the mass of the Lead Iodide. It was found that when the concentrations of each are 5:5, the filtration leaves a substantial amount of the liquid and the yellow precipitate known as lead iodide is at the peak of the masses.
The interesting part of the experiment is that it was far from expected results. It was conducted by three classes and the data varied across the chart. The last test group was not able to be used because of the inconsistency in which the obtained measurements compared to those of the rest of the tests. Therefore, only two classes were compared. The 4th period was seen to be the most accurate. The first two measurements, those of 1:9 and 2:8 varied greatly. The following masses compared were similar yet period 3 were all a little lower until the last concentration level measurements which were almost exactly the same
The mistakes prevalent in the lab are not due to the experiment itself. Rather, it is human error that can be held accountable for the drastic differences. One of the reasons is improper measuring and mixing to begin. The students may not have gone to eye level to read each mark carefully to ensure only the most exact measurements. Also, the pipette is made of glass. This calls for the meniscus to be read properly or else the measurements will be off. To avoid confusion of the meniscus with graduated cylinders, plastic would be most appropriate. Luckily, these are hydrophobic and without a meniscus, they are simple to read. If glass was used, then it would leave open some opportunities for mistakes. With the pipettes, there could have easily been bubbles. The bubbles would take up space where the liquid should be for precise measuring.
If twisted the wrong way, it would be easy for air to get trapped and cause these pockets. The pipettes however are carefully crafted so that the markings are a little above where they should be. Taking that into consideration, the room for error in not allowing all the water to drip out of the pipette, if done properly, is eliminated. Another space for error is the filter papers. Some of them were larger than the others. This can distort the results. The same filter paper should be used for all of those participating in the tests.
The papers also varied in thickness. Others used only one paper, allowing too much precipitate through, and others used more than two. This allows the paper to absorb too much liquid instead of filtering it all the way through. An additional problem is evaporation. Leaving the filtration apparatus uncovered could allow gradual evaporation. Quite oppositely, the humidity in the room could also cause tampering with the solution. With the weather changes, the temperature of the lab was not held at a constant. One day it was heated the next was at a very cool temperature. This could easily have an effect on the experiment.
All these reasons could have a great deal in the variety of results. The experiment would need to be performed again to accurately portray the data. Human error would need to be nonexistent
As previously stated, the results of the experiment were not all in agreement. The different classes obtained various results. This can be due to human error. After realizing the effects on the reaction taking place, it was also discernable how concentration can easily affect the combination. However valuable knowledge on the formation of lead iodide was gained from this lab and the purpose was successfully completed.