To what extent does the dissolved oxygen content (mg/L) of three different water samples change when introduced to increasing concentrations of Manganese Sulfate (MgSO4), as measured by an Oxygen Meter?
1: Introduction
I was first intrigued by this topic during the Group Four project, specifically the chemical component of how we could determine the quality of water from local bodies of water. I found that many of the pollutants we allow to mix with water cause a decreased quality of the water, in turn causing problems for many ecosystems and organisms. As I live in a rural area, the local bodies of water were often subject to increased levels of Manganese (II) Sulfate (MgSO4), an active component in many fertilizers. The dissolving of Manganese Sulfate is as follows below:
Looking this particular reaction, I wondered if the amount of oxygen would increase or decrease. My interest in this substance and its significance when added to water was piqued, which is why I decided to delve further into research done with this. I found two methods routinely used to test the DOC (dissolved oxygen content) of water samples, the Winkler Method and the Oxygen Meter. I originally chose to use the Winkler method as it allowed for more of a hands-on approach, but due to the chemical properties of certain required substances, I opted for the meter method instead. Given the statistical and ecological importance of water quality for both plants and animals alike, I questioned to what extent these reactions can be isolated from outside factors in order to determine the impact of this sole substance on water quality. This led me to my research question: To what extent does the dissolved oxygen content (mg/L) of three different water samples change when introduced to increasing concentrations of Manganese Sulfate (MgSO4), as measured by an Oxygen Meter?
2: Investigation
2.1: Hypothesis
H1: As the added concentrations of Manganese (ll) Sulfate are increased, the level of dissolved oxygen content for all the water samples alike will decrease.
H0: As the added concentrations of Manganese Sulfate are increased, the level of dissolved oxygen content for all the water samples alike will have statistically significant change.
The reaction under study is as added to water in concentrations of 0g (which functioned as a control), 10g, 20g and 30g to samples of 200mL from three different water sources: distilled, water sample A, and water sample B.
Both water samples are from local bodies of water, which are discussed further on in the investigation.
2.2: Background Information
Previous research has shown that the addition of sulfates to water bodies has caused toxicity to the aquatic ecosystems found in the same body of water. However, no previous research has used Dissolved Oxygen Content (DOC) as a signifier towards the water quality, as majority of studies have been focused towards to impact of the substance on underwater plants and animals as opposed to highlighting the water quality. The DOC refers to the amount of oxygen found within water, and is a good quality indicator as highly aerated water, or water surrounding with a rich oxygen setting, is needed for cell respiration.
The six carbon atoms and twelve hydrogen atoms within the glucose make it possible to form the six molecules of carbon dioxide and six of water. The amount of oxygen needed would come out to be 18 atoms, which means you need an addition 12 oxygen atoms in the reactant side. However, the reaction involving MgSO4 is an exothermic reaction and releases heat. This, in addition to changes within the acidity levels and toxicity of water decrease the dissolved oxygen content.
Additional necessary background information includes information on the areas of the three water samples. The distilled water comes from a company called President’s Choice, which collects the water from Grey Highlands in Ontario, Canada. I collected the water sample A from Heart Lake Conservatory Centre in Brampton, Ontario. The last area water samples were collected from is a local storm water pond in Caledon, Ontario. All of these are from the same underground aquifer, The Great Lakes Basin, which means that they are all interconnected underground in one way or another – thus showing the importance of chemicals added in one body of water, as they can eventually reach and damage the purity of our underground aquifer. This is further depicted in diagram 2.2.1 on the following page.
A D.O sensor, or a dissolved oxygen sensor, consists of a semi-permeable membrane, a light-emitting diode (LED) and a photodetector. Within the sensor is a luminescent dye that is immobile, but reacts when exposed to the blue light emitted by the LED. This works because it causes a limitation of the intensity and lifetime of the luminescence, which is recoded by a photodetector and can be used to calculate the DOC. This is depicted in diagram 2.2.2 on the following page. However, I was not satisfied with this explanation, and when further researched I discovered the measurement of concentration of dissolved oxygen, as measured by partial pressure, is inversely proportional to luminesce lifetime. has been proven by the Stern-Volmer equation. This is best explained with the use of diagram 2.2.3. on the following page.
2.3: Variables
Independent Variable: The independent variable is the amount of Manganese Sulfate added into the samples of water. This is because in order to determine the impact of concentrations level on dissolved oxygen levels, an array of concentration amounts was needed. I shoes Manganese Sulfate because of its importance and widespread use within fertilizers, but also because sulfates have been proven to be toxic to aquatic ecosystems, and I also wished to explore how that reflected in water quality.
Dependent Variable: The dependent variable is the amount of dissolved oxygen present within the water sample after certain concentrations of MgSO4 (s) have been added. By using the dissolved oxygen content as the measurement of choice, not only can we detect a trend towards degradation of water quality, but also see the impact on the water itself as opposed to using a specific organism’s health/reproduction cycle in reflecting on the toxicity, as has been done in previous reports1.
Controlled Variables:
1. Temperature of reactants: The temperature of the reactants was kept constant at room temperature, with the lake water being left in room temperature for 24 hours prior to the experiment with the use of closed Erlenmeyer flasks, in order to be the same temperature as the distilled water samples, which were also kept in closed Erlenmeyer flasks for consistency sake. Room temperature was measured as 22.9ºC in the duration of the 24 hours, with any fluctuations being insignificant. The reason they were left in closed flasks and not heated was because heat can drastically change the DOC levels, and so can aeration. This means the samples would be kept in closed flasks for the experiment, and heating a closed flask was both dangerous and not an option.
2. Volume of Water Samples: This was all kept the same, 200 mL with 0.01 uncertainty.
3. pH: the pH from the distilled water measured at 6.9, making it almost neutral. However, the pH of MgSO4 (s) is slightly acidic, between 5.5 – 6.5. Due to this, a buffer solution was added in the moments before the reading was taken, so not to disrupt the amount of oxygen yet maintain the same level of pH. This was confirmed through readings on the DO sensor, which could be programmed to show a screen measuring pH levels.
4. Light/Luminescence: Since this sensor worked based of off exposure to light, I made sure the samples were kept under shade from the same amount of light when in the classroom. Prior to the classroom, I kept the water samples in a dark colored fabric bag, so to prevent extreme exposure to light.
4: Methodology
4.1: Apparatus
1. 16 of the 250 mL Erlenmeyer flasks (0.01)
2. 16 rubber stoppers
3. Weighing boat
4. Electronic weighing scale (0.01)
5. Manganese (ll) Sulfate
6. 800mLDistilled water
7. 800mL Water sample A
8. 800mL Water Sample B
9. D.O sensor
4.2: Photographs of procedure and set-up
4.3: Experimental Procedure
1. I began by taking the 800mL sample of distilled water, and pouring 200mL into four of the 250mL Erlenmeyer flasks, making sure to tilt the Erlenmeyer flask so that the water runs down the inner side of the glass. Then, I Immediately sealed the flask. This prevented aeration of the water, and helps avoid systematic error when measuring the DOC.
2. The next step I did was to label each individual flask with the water sample name, in this case distilled water, and the amount of MgSO4(s) to be added. This was in increments of ten, starting from 0.00g to 30.00g.
3. I then repeated steps number one and two for the remaining two water samples, water sample A and B.
4. After waiting for the duration period of 24-hours, I checked the temperature to ensure that all samples matched the room temperature, which was 22.9ºC on that day. This was done with minimal exposure to air, and the exposure to light was kept constant (they did not come out of the shade).
5. Once confirming that the 24-hour period did not need to be extended, I then used a weighing boat to measure out exactly 10.00g of MgSO4(s) to be added in the respective flask for distilled water.
6. In order to add the crystalline powder substance, I used a metal spatula which would not react with the substance. I started by tipping the flask, so that the water did not cover the entirety of the bottom of the flask. I took a small amount of the substance using the metal spatula and brought it down until the metal tip holding the powder touched the exposed glass bottom. Then, I slowly tipped the water back upright, so the substance would dissolve because if I were to mix the substance my swirling or by using a stirring rod, it would create aeration and I would have to discard that sample. The final positioning is shown in diagram 4.2.1.
7. I repeated step five for concentrations of 20.00g and 30.00g.
8. I then further repeated steps five to seven for water samples A and B.
9. Since the reaction of MgSO4(s) with H2O(l) is an exothermic one, meaning it released heat, I waited for around 30 minutes for the temperature to return back to 22.9ºC (the room’s temperature). At the end of the 30-minute period, I measured the temperatures of the liquids to ensure they were suitable to continue with.
10. Once the solutions have been prepared, I began measuring using the D.O sensor. I did this by first following the procedure which came with the kit, that allowed me to input predetermined sensor constants.
11. After carefully following the instructions, I washed and dried the sensor gently, using distilled water. This was to ensure no residue from previous experiments interfered with my current one. However, doing this changed the sensor’s D.O reading, after which I waited for it to return to the setting of the room. This is shown in diagram 4.2.5.
12. Once the sensor had been cleaned and had settled to the reading of the room, I carefully inserted it into the glass flask. This was done with precision and accuracy but not at a great speed, so that the reading would not be impacted, as the sensor is very sensitive. The sensor was a snug fit into the opening of the flask, which helped reduce oxygen exposure. This is shown in diagram 4.2.4.
13. Once the reading had stopped fluctuating, I noted down the D.O.C in mg/L as shown on the monitor.
14. I then removed the sensor and stopped the flask once again. I then continued to repeat steps 11 – 12, with the next reading being the 10.00g concentration of distilled water. These steps were repeated until five trials for distilled water had been recorded.
15. I then repeated step 14 for all water samples of A and B with the varying concentrations. These too were noted down.
4.4: Risk Assessment
Safety Considerations: The chemicals and solutions used should be handled with care, not mixed unless intentional and with gloves, protective clothes, goggles on at all times. This is because MgSO4(s) can be irritating to eyes and skin with exposure, as stated in the MSDS of the substance. This is also to ensure I was not exposed to any unknown chemicals found in water samples A and B.
The bottles are made of glass and I was also careful with their handling because dropping them, or any of the substances inside them, can become an extremely dangerous situation. It would also mean restarting the experiment, so I was always cautious and wore closed toes shoes.
Ethical Considerations: Since my IA was regarding the environment, and related back to the bigger picture of pollutants impacting our water, I wanted to ensure the companies and obtaining the substances was done as ethically as possible, such as adhering to the ethical guidelines set in the manufacturing industry and within the scientific community. I did this by reading up on all rules and regulations for both my chemistry IA, as set by IB headquarters, and also the guidelines on scientific procedures within the community. My experiment adheres to both guides.
Environmental Considerations: I made sure to dispose of all chemicals in the correct manner, as opposed to spilling them outside or down the sink which has the possibility of returning in our school’s drinking water, or eventually, back to the GTA’s underwater aquifer.
5: Raw Data
Table 5.1.0: A raw data table showing the concentrations of MgSO4(s) alongside the corresponding dissolved oxygen content for each respective water sample catagoery, organized by trial number.
DISTILLED WATER
(all samples have a volume of 200ml ()
WATER SAMPLE A
(all samples have a volume of 200ml ()
WATER SAMPLE B
(all samples have a volume of 200ml ()
Amount of MnSO4•H2O (
0g
10g
20g
30g
0g
10g
20g
30g
0g
10g
20g
30g
Trial 1 (
4.18
3.94
3.74
3.40
4.32
3.75
3.29
2.48
3.84
3.75
3.42
2.75
Trial 2 (
4.84
3.90
3.82
3.51
4.36
3.82
3.49
2.96
4.22
3.79
3.82
2.81
Trial 3 (
4.63
4.05
3.87
3.62
4.59
3.96
3.62
2.58
4.49
3.85
3.72
2.64
Trial 4 (
4.79
4.21
3.96
3.79
4.72
4.29
3.79
2.73
4.53
4.32
3.84
2.73
Trial 5 (
4.92
4.38
4.05
3.88
4.89
4.42
3.96
2.89
4.62
4.40
4.02
2.91
Graph 5.1.0: A graph organized all raw data points, for further analysis.
5.1: Qualitative Observations
1. As concentrations increased, more time was needed to allow for dissolving.
2. Water sample B, which came from the storm water pond in Caledon, was already slightly murky to begin with. This could explain the larger range of data points for that sample.
3. The heat released from each reaction varied based on the amount added. E.g., 30.00g released the most heat, while 10.00g released the least and 0g released no heat at all. (nothing was added to the 0g flask) This was consistent regardless of where the water sample came from.
4. The part of the probe needed to make a reading was submerged within the solution, but not the entirety of the sensor.
6: Processed Data
Table 6.1.0: A processed data table showing the concentrations of MgSO4(s) alongside the corresponding dissolved oxygen content for each respective water sample category, organized by trial number – with the trials’ mean number shown.
DISTILLED WATER
(all samples have a volume of 200ml ()
WATER SAMPLE A
(all samples have a volume of 200ml ()
WATER SAMPLE B
(all samples have a volume of 200ml ()
Amount of MnSO4•H2O (
0g
10g
20g
30g
0g
10g
20g
30g
0g
10g
20g
30g
Averages (
4.672
4.096
3.888
3.640
4.576
4.048
3.630
2.728
4.340
4.022
3.764
2.768
The software previously used to depict all data points was not able to produce a clear, coherent graph while also providing calculations needed in section 6.1, so a different online software was used for the processed data graph.
Graph 6.1.0: A graph organized all mean data points, for further analysis.
6.1: Processed Data Calculations
DISTILLED WATER WATER SAMPLE A WATER SAMPLE B
An online calculator was used to calculate the lower values, with an online graphing software to calculate the mathematical analysis in the upper three boxes. The line of regression calculations does not differentiate from one water sample to another as I wanted to include all as one data set, in order for analysis on the overall impact and correlation of the variables. Both websites have been used in school and are popularized websites, so I used them as opposed to others because this would mean it has gone through many people and the calculations are correct.
Although the average for distilled water, 30g trials seems to be an outlier, I opted to keep it in the calculations because it was the average of five data points, not just one. Not to mention, when we consider the data point logically, it can be presumed that Water Sample A and Water Sample B could have had additional run-off or chemical substances already present, causing the result of the 30g trial to be more extreme for them as opposed to the distilled water sample.
8: Evaluation
8.1: Conclusion
The extent of which increasing levels of MgSO4 impacted the Dissolved Oxygen Content of varying water samples across The Great Lakes Basin was successfully investigated throughout the experiment and as detailed in this report. Although the R2 Value cannot speak directly to causation, when evaluated alongside background knowledge and alongside previous reports, it can be said there is an extremely high indicator towards causation between the X and Y variable. Overall, this means that my null hypothesis can be successfully rejected and the original hypothesis accepted.
There is a relatively high systematic error, due to the uncertainty on the oxygen metre not being indicated on the apparatus, nor on the supplier’s website. It was estimated around 0.05, through the help of my teacher supervisors. However, despite this, I still feel confident in my results due to their precision, which is indicated through the relatively low standard deviance and variance, along with the high R2 value. Although the value is negative, this means it verifies my hypothesis about the DOC level decreasing. This experiment is also in consensus with current scientific knowledge, regarding the excess of minerals found in fertilizers and run-off to be harmful to the quality of water for plants and aquatic life alikei. The age of the study that I used to fact check my results is also reliable, as indicated by the age of the study and by the credibility of the authors, being written in 2010 by James Elphick.
8.2: Strengths
There were many strengths about this experiment, which helped with reassuring the results were in the correct path. The experiment had a low standard deviation (s) and variance (s2) in the calculation for each of the water samples against the levels of MgSO4. The random error was low for most of the apparatus used, as indicated on graphs and raw data table labels, which also helped to increase the certainty of the conclusion drawn in 8.1. Furthermore, with the R2 value strongly presenting itself at a negative correlation of 0.9 demonstrates the accuracy and the strong correlation between the two variables.
8.3: Weaknesses
However, there were a number of weaknesses.
The temperature of the room, although strongly estimated to have stayed at room temperature, could have fluctuated unbeknownst to me as other people and classes were going on. The reason for this being a weakness is that temperature impacts the gas content of water, and although the temperature was measured every two hours, it was not strictly monitored.
The makeup of the solutions could have been altered based on where I took the samples from, as they were taken from the surface of the bodies of water, which may have skewed my results towards having a higher oxygen level than if the samples were taken from the bottom of the pond.
Furthermore, the pressure of the samples were not measured or monitored. This could have caused a change in the levels of oxygen as the corks used to seal the samples while they cooled from the addition of MgSO4 may have changed the gas content in the samples.
8.4: Extensions and Limitations
A possible extension to this experiment could be broadening the scope at which samples are collected geographically, so to determine how this change can vary over geographical locations across Canada. This knowledge will help in understanding and further refining the chemical we use to grow our food, as it impacts both wildlife and our water.
However, a current limitation of this investigation is that it uses technology as opposed to the titration method of the Winkler Method, as that could allow for a better visualisation of small water samples, whereas the meter excels more when used in larger bodies of water.
9: Bibliography
- “Chegg.com.” 1. Magnesium Sulfate Can Be Dissolved In In Water … | Chegg.Com, www.chegg.com/homework-help/questions-and-answers/1-magnesium-sulfate-dissolved-water-make-hot-pack-according-balanced-chemical-equation-mgs-q5498210.
- “Dissolved Oxygen.” Environmental Measurement Systems, www.fondriest.com/environmental-measurements/parameters/water-quality/dissolved-oxygen/.
- Elphick, James R., et al. “An aquatic toxicological evaluation of sulfate: The case for considering hardness as a modifying factor in setting water quality guidelines.” Environmental Toxicology and Chemistry, vol. 30, no. 1, Sept. 2010, pp. 247–253., doi:10.1002/etc.363.
- Feinstein, Daniel. USGS Ground water in the Great Lakes Basin : the case of southeastern Wisconsin, wi.water.usgs.gov/glpf/objectives.html.
- “Great Lakes Basin.” Http://Www.yellowmaps.com, Http://Www.yellowmaps.com/Maps/Img/CA/Regional/Greatlksbasin.jpg, www.yellowmaps.com/maps/img/CA/regional/greatlksbasin.jpg.
- “Measuring Dissolved Oxygen.” Environmental Measurement Systems, www.fondriest.com/environmental-measurements/equipment/measuring-water-quality/dissolved-oxygen-sensors-and-methods/.
- “PC Distilled Spring Water.” President’s Choice, www.presidentschoice.ca/en_CA/products/productlisting/pc-distilled-spring-water.html.
- “Regional government Map of Great Lakes Basin.” Great Lakes Basin Regional Map, www.yellowmaps.com/map/great-lakes-basin-regional-map-655.htm.
- “Sulfate_sulphate_toxicity.” Sulfate_sulphate_toxicity, www.researchgate.net/post/Sulfate_sulphate_toxicity_on_trout_and_other_fish.
- “What is the chemical equation for cellular respiration? | Socratic.” Socratic.org, socratic.org/questions/what-is-the-chemical-equation-for-cellular-respiration.
9.1 Endnotes (MLA)