Project 1: Inorganic Containments Present in Water Samples
Introduction
Background:
Chemistry is commonly used when it comes to testing in a laboratory. Scientist use many different ways to determine what an unknown substance is. Looking at the qualitative properties of the substance such as the color, smell and other properties that can be observed and not measured is one way. However, looking at the quantitative properties, measurable portion of testing like moles or melting point, also contribute to the identification process of finding out what an unknown substance is. When looking at substances that are hazardous to wildlife we can use the method of Spectroscopy which is when light interacts with an unknown substance (1). This is an example of a qualitative test because you observed the difference that one substances has with certain types of light. When the police seize unknown substances from criminals or in drug raids they need someone to confirm the identity of these substances. Unknown powders, liquids and even pills that could be potentially illegal would be confirmed by forensic labs. There are two types of test they usually use which are presumptive tests and confirmatory tests. However, unlike presumptive tests, confirmatory tests are very specific and allow the forensic lab to determine the exact identity of the substance (2).
Theory:
There are four tests that will make up the qualitative procedures of this experiment. These include solubility, conductivity, pH, and a flame test. The unknown compound we had was white in color and had a baking flour appearance meaning that it was fine. These will all be used to help weed out the other unknown substances from a few that would be able to give you a general direction. Solubility tests are generally used to see how soluble the substance is in deionized water. The conductivity test is used to measure the dialysis fluids, according to PubMed.com a dialysis fluid is a solution of salts that are dissociated (3), total concentration of salts. The next test is pH and which measures the pH level of the solution that we made and this helps us narrow down if the substance is an acid base or neutral which will further narrow our choices. A flame test shows us the color of a substance by putting it directly into the flame and each substance has a different color that will appear. Next will be the test that will be the two quantitative procedures of the experiment. Gravimetric analysis is based on weight where Volumetric analysis is based on volume. Volumetric was the one we used since discovering that the unknown we had basic or acidic properties.
Hypothesis:
Since the portions of our experiment gave us an assumption that after all the test that our unknown substance is Magnesium sulfate (MgSO4) since it did not have the signature smell.
Objective:
Week one our goal were to get an idea of what our unknown substance was after all the qualitative experiments. After week one we had a general thought of which of the two substances it would be between. However, week two the goal was to figure out which quantitative experiment worked for us the best and that ended up being the volumetric. Then to proceeded to figure out our substance.
Methods
Part I Methods:
We began the experiment with the solubility test and we started by putting 0.5g of the unknown substance and then 49.5g of deionized (D1) water into a beaker then decided that it was soluble in water. We repeated this same measurements of 0.5g of the unknown substance with 49.5g acetone and ethanol in a beaker but both resulted in the substance being clumpy and could not dissolve into a solution making it insoluble. This helped us minimize options for what the unknown substance could be. Next we made a solution with D1 water and the substance to test the conductivity and pH, we used 70 mL of water with 0.5g of the substance to make our base solution and we conducted the experiment by using the conductivity meter and the pH meter. Using only one at a time, we would turn it on, stick it into the solution, and waited until it gave us an answer. This showed the conductivity helped determine the conductivity of the substance and the pH helped determine if the acid base or neutrality of the substance. The flame test shows if the substance has a reaction to the flame which will result in the flame changing colors. We used a wire loop to get a little bit of the solution with the substance and then placed it in front of the flame.
Part II Methods:
Finally we gathered the information collected from previous experiments and we decided to conduct the volumetric analysis. We used a solution of .5g of the substance with 70mL water so that it was fully dissolved. Then we added 10 drops of Silver nitrate l into a beaker to get the mixture that we would let drop into our solution.
Safety:
Chemical Name
Chemical Formula
Molecular Weight
Potential Hazards
Saftey Equipment Needed
Magnesium sulfate
MgSO4
120.366 g/mol
-inhalation
-Skin
-Eyes
-Ingestion
Gloves, goggles, full lab gear
Hydrochloric acid
HCl
36.46 g/mol
-Corrosive
-Skin
-Eyes
Gloves, goggles, full lab gear
Sodium hydroxide
NaOH
39.997 g/mol
– Inhalation
– Corrosive
Gloves, goggles, full lab gear
Ethanol
C6H6O
94.11 g/mol
– Flammable
-Vapor/air mixtures are explosive
– Inhalation
Gloves, goggles, full lab gear
Acetone
C3H6O
61.057 g/mol
– Inhalation
– Skin
– Eyes
Gloves, goggles, full lab gear
Silver nitrate
AgNO3
169.87 g/mol
-Skin
-Eyes
– Headache, dizzieness and nausea
Gloves, goggles, full lab gear
Results
Section I:
CONDUCTIVITY AND pH (AVERAGE of 3 Trials):
FLAME TEST:
UNKOWN
TRIAL
COLOR
———-
1
No Color
———-
2
No Color
———-
3
No Color
SOLUBILITY TEST:
COMPOUNDS
ACETONE
ETHANOL
H2O
NH4Cl
YES
YES
YES
Ca(NO3)2
YES
NO
NO
MgSO4
NO
NO
YES
CaCl2
YES
YES
YES
Na2CO3
NO
NO
YES
CH3CH2Na
NO
NO
NO
UNKOWN
NO
NO
YES
CALCULATIONS:
0.1M * 100/1000L = .01 mol *40g/mol = 0.4g
0.1M 100mL NaOH
Section II:
FILTER PAPER
TRIALS
WEIGHHT (g)
1
0.67g
2
0.65g
3
0.66g
Calculations:
Median: 0.66g
Discussion
Part I Discussion:
In the experiment when we tested the conductivity we did three trials and our end result was 8.83 s/m. Also the pH was at a 9 which the known pH of magnesium sulfate is between 5.5 and 6.5. The pH that we got was higher for the unknown than the known pH of MgSO4. When conducting the flame test we witnessed that there were no color on any of the trials that we got. Which the purpose of this test is to observe the color that is given by the compound that we had. The result matched up with either ammonium or magnesium. The next test was the solubility test in which we tested the unknown substance on how soluble it is in ethanol, acetone, and water. We conducted the test to see that it only is soluble in water just like MgSO4.
Part II Discussion:
Finally the last test was the volumetric test and this ended up showing us the precipitant weight that we got out of this experiment. We got a medium weight of 0.66g.
Source of Error:
At the beginning of experimenting we were using regular tap water instead of deionized. We observed that this did indeed change our results so to fix our mistake we grabbed D1 water so that everything would be the same and our results would not be wrong.
Changes to the Experiment:
I would probably change the experiment to where there would be certain amounts for certain substances. It made it difficult to know that the measurements of how much water is supposed to be in the beaker was different.
Conclusion
The purpose for this experiment is to get a better understanding of the tests that we used but the goal was to find what substance was our unknown and how we achieved that answer. I learned a lot of new things in this experiment with how to conduct then to how to put them into work to compare. All of our data matched up to what we believe to be is MgSO4 as our unknown substance. We used the skills that we learned to conduct the experiments to get this result.
Research Connected
In the article A Framework to estimate concentrations of potentially unknown substances by semi-quantification in liquid chromatography electrospray ionization mass spectrometry (4), this article focuses on if it is possible to find the concentrations of an unknown substance within sources that rely on quantitative information. The procedures that they did were to use liquid chromatography, which is a technique used to separate ion or molecules when they are in a solvent (5). They also used statistical analysis, nozzle voltage, sheath gas experiments and more. However, in the article it did mention that they used general screening methods but not all compounds deionized in water which will make it hard to detect them. Authentication standard is making the unknown substances harder to work with. Using LC-MS quantification they were able to contain the concentration of 300 potential AOI with no use of matching or prior identification. However, estimation errors are still something that needs to be focused on because it would improve the predictions.
References
1) Libretexts. (2018, November 26). 10.1: Overview of Spectroscopy. Retrieved February 19, 2019, from https://chem.libretexts.org/Bookshelves/Analytical_Chemistry/Book:_Analytical_Chemistry_2.0_(Harvey)/10_Spectroscopic_Methods/10.1:_Overview_of_Spectroscopy
2) Watson, S. (2018, March 08). How Forensic Lab Techniques Work. Retrieved February 19, 2019, from https://science.howstuffworks.com/forensic-lab-technique2.htm
3) Bertinsson, G. I. (n.d.). The conductivity of dialysis fluid. Retrieved February 20, 2019, from https://www.ncbi.nlm.nih.gov/pubmed/16083025
4) A framework to estimate concentrations of potentially unknown substances by semi-quantification in liquid chromatography electrospray ionization mass spectrometry. (2017, April 10). Retrieved February 19, 2019, from https://www.sciencedirect.com/science/article/pii/S000326701730452X
5) Chemistry Dictionary. (n.d.). Retrieved February 20, 2019, from https://www.chemicool.com/definition/liquid_chromatography_lc.html
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