Research Question:
How does the concentration of sodium hypochlorite (NaClO) impact the rate of its reaction with red food dye (C18H14N2Na2O8S2)?
Background:
Chemical Equation
NaClO(aq) + C18H14N2Na2O8S2 (l) —-> C18H15N2Na2O9S2 (aq)
According to collision theory, reactions occur when the reactants hit each other with sufficient velocity and the correct orientation. For the reaction to occur, the energy of the particles must be greater than the activation energy of the reaction; therefore, if the average energy of the system is increased, or if there are more reactants with sufficient energy, the rate of the reaction will increase. The rate of a reaction is known as the change in concentration over time of either the products or reactants and is directly correlated to the initial concentration of some or all of the reactants. This means that if the concentration of one of the reactants is increased, the rate of reaction will increase as well. The rate of reaction can be calculated by finding the change in concentration of reactions over time.(Brown) This investigation varies the concentration of sodium hypochlorite to see how it affects the rate of the reaction with red food dye.
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Since the rate of disappearance of reactants will express the rate of reaction in this experiment, the amount of time that the solution will decrease in color when it is measured. This equation will be Rate = k [C18H14N2Na2O8S2]a [OCl–]b as the exponents will represent the molecularity and the k will be the rate constant at room temperature. Comparing this rate at different molarities will portray the relationship between concentration and time.
A colorimeter will be used and it can measure the concentration of a solution with the quantity of light that beams through a solution given a reference point. A cuvette is used to hold the solution being measured inside the colorimeter. It is essential to address that the environment where the experiment is taking place should not be bright because external light can impact the dependability of the readings.
Sodium hypochlorite (NaClO), commonly known as bleach, has oxidizing properties that break the double bonds of a chromophore and make the chromophore colorless with time. One of the electrons from the dye will be transferred to the beach, which is another factor that causes the color to fade.
This experiment sparked my curiosity about how different concentrations can affect the time it takes for the colored food dye to disappear. Bleach is used in everyday life and this experiment portrays its strength in action and will allow it to be quantified. Working with dyes is visually pleasing and since it is food dye, it is present often in our everyday lives.
Variables
Independent variable: Concentration of NaClO, measured in molar (M, mol L-1). — 0.174 M, 0.348 M, 0.522 M ,0.696 M, 0.870 M NaClO; this will be varied by diluting 0.870 M NaClO with distilled water.
The molarities were calculated with the following steps:
Bleach has a density of 1.08 g/ml can be converted to 1080g/L. NaOCl has a molecular weight of 74.44 g/mol.
Calculated mol/liter (molarity) —
1mol74.44g
x 1080g/L = 14.5M
Household bleach is a solution of about 6% NaOCl (A dilution of 6 parts in 100).
To calculate the concentration of dilute solutions —
(m1)(v1)=(m2)(v2)
.
In this case: (14.5M)(6) = (xM)(100). x=0.87M.
The 0.870M was diluted into 5 variations – 0.174M, 0.348M, 0.522M ,0.696 M, and 0.870 M
Dependent variable: Change in absorbance (Unitless), the raw data will be recorded by
the colorimeter and then calculated to find the average change for each concentration.
Constants
Why is this being held constant?
How is this being held constant?
Drops of food dye
The number of drops of the food dye has to be held constant because the variable that is being changed is the dilutions of bleach and changing the mass of the food dye would alter the aim of the experiment.
This is being held constant by making sure that each trial has 2 drops of red food dye being dispensed into the diluted bleach.
Environment
Having the surroundings of the experiment remain constant will prevent any outlying factors from impacting the product. For example: temperature, workspace, etc. Temperature affects the reaction rate.
Also, environmental light would affect the reliability of colorimeter readings.
All trials were performed in the same lab at approximately room temperature with the same amount of ambient light. The room temperature in the workspace for this experiment was about 25 degrees Celsius (Measured by thermometer at the start of the experiment)
Colorimeter used
Different colorimeters, like the balance, have different uncertainties. If only one colorimeter is used, it limits the variety of uncertainty in the experiment.
Using the same colorimeter will prevent various amounts of uncertainty.
Dilution Table:
Desired concentration of NaClO
Volume of concentrated NaClO
Volume of water
0.174 M
10 ml (Diluted from 0.870M)
40 ml
0.348 M
20 ml (Diluted from 0.870M)
30 ml
0.522 M
30 ml (Diluted from 0.870M)
20 ml
0.696 M
40 ml (Diluted from 0.870M)
10 ml
0.870 M (Not diluted)
50 ml (Diluted from 0.870M)
0 ml
Sample Calculation — 0.870M
Using the formula M1V1 = M2V2, we can find how many milliliters of a given concentration (NaClO) is necessary for the desired volume and concentration. For example, if we wanted to produce 50 mL of 3 M NaClO from 5 M NaClO, we would do the following calculations:
M1V1 = M2V2
(0.870 M)(V1) = (0.522 M)(50 mL)
V1 =
50 (0.522)0.870
= 30 mL of 0.522 M HCl, and
Vwater = V2 – V1 = 50 – 30 = 20 mL of water.
Using the same calculation, to produce 50 mL of 0.522 M HCl, we would need 30 mL of 0.870M NaClO and 20 mL of water.
Procedure:
Gather the materials.
Turn on your datalogger and connect it to the colorimeter. Ensure that the display on the datalogger is set to Absorbance.
The colorimeter needs to be calibrated with a reference point (or a “0”).
Measure out 4 ml of distilled water with a graduated cylinder and dispense into the beaker. Use a magnetic stirring rod to stir the solution for 5 seconds. Take off the top of the cuvette slot to prepare to insert the solution.
Put the mixture from the beaker into a cuvette and place it carefully into the colorimeter. after it is properly inserted, put the top back on the cuvette slot.
Select the appropriate color wavelength (the color wavelength is opposite that of the color of the solution) so, for this experiment the wavelength would be blue because the color of the solution is red.
Adjust the wavelength to the maximum absorbance (should be around 440 – 460 nm) but if your colorimeter only gives you set options, choose the option closest to 450 nm. (Van Nostrand)
The colorimeter in this experiment had a maximum absorbance of 420 nm.
Press the CAL button on the Colorimeter to begin the calibration process and release it when the red LED begins to flash. (close to 100% transmittance or 0 absorbances)
Remove the cuvette from the colorimeter and dispense the solution into a sink. Clean the cuvette to prepare it for future use.
We are going to start at 0.870 M.
Referencing the dilution table above, we will use a volumetric flask and measure out 50 ml of 0.870 M.
Pour this in a beaker and squeeze two drops of red food dye into the mixture.
Immediately after, mix the mixture for 5 seconds.
Dispense the mixture into the cuvette until it has reached it is ¾ full. Be careful not to overfill.
Slide it into the cuvette slot in the colorimeter and click START on your datalogger. Log data until there curve is no longer changing.
Repeat Step 6, two more times for two more trials. (3 total)
The rest of the solutions are slightly different because there is water being added to dilute the 0.870 M NaClO. This next process is for 0.696 M NaClO.
Referencing the dilution table above, we will pour 40 ml of 0.870 M in a graduated cylinder. In the second graduated cylinder, pour 10 ml of distilled water. Combine these two into a volumetric flask. Grab the volumetric flask by the neck and gently swirl the mixture around a vertical axis for 20 rotations.
Pour this in a beaker and then drop two drops of red food dye.
Gently swirl the mixture for 5 seconds.
Dispense the mixture into the cuvette until it has reached it is ¾ full. Be careful not to overfill.
Securely slide it into the cuvette slot in the colorimeter and click START on your datalogger. Log data for 300 seconds.
Repeat Step 7, two more times.
Repeat step 7 with the other concentrations. (0.522M, 0.348M, 0.174M)
Reference the dilution table for all the measurements.
The final amount of solution in the volumetric flask should always be 50ml.
Changes from Trial Zero:
Originally, I had planned on recording only 30 seconds of data to optimize the time given to experiment. However, objectively looking at the overall process, 30 seconds would not be sufficient to look at a reliable change and confidently be able to determine the pattern. Providing more time for the trials to happen will give a lower amount of uncertainty to the data.
There was also an issue due to a lack of equipment that will decrease uncertainty so instead of using an automatic pipette as planned, the red food coloring dropper was used.
Safety:
Safety is important in this investigation as the chemicals in use such as sodium hypochlorite (NaClO) can be harmful in contact with skin, eyes, or internal organs. The higher the concentration of the sample, the greater the risk. If undiluted bleach comes into contact with skin, the area needs to immediately be cleansed with water. If it isn’t cleaned, it can permanently damage skin tissue and lighten the skin pigmentation. Make sure to close the containers of bleach after use because bleach fumes can irritate the lungs.
Be careful not to let any liquid get near electrical devices, especially the Colorimeter. (Except for the cuvette which will have liquid in it but will be dry on the outside.) If an accident does happen, disconnect the Colorimeter immediately, open the cuvette compartment and try to get as much liquid out as possible and let the equipment dry. When it has dried, it can be tested on but make sure that there is no chemical corrosion before use.
Wear aprons and use trays because food coloring can stain clothing. Remove all jewelry to ensure that there is no possible contamination. Always wear goggles and dispose of products properly. Do not pour undiluted bleach down a drain, it can mix with other chemicals and cause hazards. Diluting the solution with a lot of sink water before pouring it down the drain will prevent any accidents. Do not ingest any materials in this lab.
There are no ethical issues in this lab because no living organisms are/were tested on.
Raw and Processed Data:
Calibrated Colorimeter Table
Calibrated Absorbance ± 0.001
Trial 1
Trial 2
Trial 3
Average
-0.001
-0.001
-0.001
-0.001
Table 1: raw and processed data showing the rate of reaction for 0.870 M sodium hypochlorite
0.870 M NaClO
Trial 1
Trial 2
Trial 3
Average (Calculated)
Raw Data
Water(mL)
0.00
0.00
0.00
0.00
NaClO(mL) ± .2 mL
50.5
49.5
50.5
50.2
Empty Colorimeter Absorbance ± 0.002
-0.001
-0.001
-0.001
-0.001
Number of Red Food Coloring Drops ± 1
2
2
2
2
Initial Absorbance ± 0.010
0.710
0.433
0.452
0.225
Measured bleach for cuvette(mL) ± 0.2
3.7
3.8
3.7
3.7
Final Absorbance ± 0.005
0.096
0.096
0.089
0.094
Time ± 0.002 s
300
300
300
300
Calculated Data
Change in Absorbance
0.614±0.1
0.337±0.1
0.363±0.1
0.438 ± 0.125
Rate Law (absorbance s-1)
0.002 ± 8.23%
0.001±
13.35%
0.001±
13.86%
0.001 ±
50%
Table 2: raw and processed data showing rate of reaction for 0.696 M sodium hypochlorite
0.696 M NaClO
Trial 1
Trial 2
Trial 3
Average (Calculated)
Raw Data
Water(mL) ± .2 mL
10.5
10.5
10.0
10.5
NaClO(mL) ± .2 mL
40.5
39.5
39.5
39.5
Empty Colorimeter Absorbance ± 0.002
0.147
0.145
0.160
0.151
Number of Red Food Coloring Drops ± 1
2
2
2
2
Initial Absorbance ± 0.05
0.345
0.296
0.254
0.298
Measured bleach for cuvette(mL) ± 0.2
3.7
3.8
3.7
3.7
Final Absorbance ± 0.05
0.085
0.097
0.087
0.089
Time ± 0.5 s
300
300
300
300
Calculated Data
Change in Absorbance
0.260±0.1
0.199±0.1
0.167±0.1
0.209± 0.047
Rate Law (absorbance s-1)
0.0008± 38.46%
0.0006± 50.42%
0.0005± 60.05%
0.0007± 21.43%
Table 3: raw and processed data showing rate of reaction for 0.522 M sodium hypochlorite
0.522 M NaClO
Trial 1
Trial 2
Trial 3
Average (Calculated)
Raw Data
Water(mL) ± .2 mL
20.0
20.0
20.5
20.5
NaClO(mL) ± .2 mL
30.0
29.5
30.5
30.0
Empty Colorimeter Absorbance ± 0.002
0.184
0.180
0.173
0.179
Number of Red Food Coloring Drops ± 1
2
2
2
2
Initial Absorbance ± 0.05
0.707
0.609
0.433
0.583
Measured bleach for cuvette(mL) ± 0.2
3.8
3.9
3.9
3.9
Final Absorbance ± 0.05
0.098
0.120
0.095
0.104
Time ± 0.5 s
300
300
300
300
Calculated Data
Change in Absorbance
0.609± 0.1
0.489±0.1
0.338± 0.1
0.479± 0.135
Rate Law (absorbance s-1)
0.002± 16.59%
0.002± 20.62%
0.001± 29.75%
0.002 ± 25%
Table 4: raw and processed data showing rate of reaction for 0.348 M sodium hypochlorite
0.348 M NaClO
Trial 1
Trial 2
Trial 3
Average (Calculated)
Raw Data
Water(mL) ± .2 mL
29.0
31.0
30.0
30.0
NaClO(mL) ± .2 mL
21.0
20.5
20.0
20.5
Empty Colorimeter Absorbance ± 0.002
0.212
0.180
0.183
0.575
Number of Red Food Coloring Drops ± 1
2
2
2
2
Initial Absorbance ± 0.05
0.863
1.029
1.052
0.981
Measured bleach for cuvette(mL) ± 0.2
3.9
3.9
3.8
3.9
Final Absorbance ± 0.05
0.092
0.129
0.140
0.361
Time ± 0.5 s
300
300
300
300
Calculated Data
Change in Absorbance
0.771± 0.1
0.900± 0.1
0.912± 0.1
0.861± 0.65
Rate Law (absorbance s-1)
0.003±
13.14%
0.003± 11.28%
0.003± 11.13%
0.003
(Uncertainty ≈ 0)
Table 5: raw and processed data showing rate of reaction for 0.174 M sodium hypochlorite
0.174 M NaClO
Trial 1
Trial 2
Trial 3
Average(Calculated)
Raw Data
Water(mL) ± .2 mL
40.0
41.0
39.5
40.2
NaClO(mL) ± .2 mL
9.5
10.0
10.0
10.0
Empty Colorimeter Absorbance ± 0.002
0.184
0.183
0.188
0.185
Number of Red Food Coloring Drops ± 1
2
2
2
2
Initial Absorbance ± 0.05
1.009
0.851
0.650
0.837
Measured bleach for cuvette(mL) ± 0.2
3.9
3.9
3.8
3.9
Final Absorbance ± 0.05
0.246
0.229
0.193
0.223
Time ± 0.5 s
300
300
300
300
Calculated Data
Change in Absorbance
0.763± 0.1
0.622± 0.1
0.457± 0.1
0.614± 0.153
Rate Law(absorbance s-1)
0.003± 13.27%
0.002±
16.24%
0.002±
22.05%
0.002± 25%
Sample Calculation for Change in Absorbance — (0.870M – Trial 1)
Initial Absorbance – Final Absorbance = 0.710 – 0.096 = 0.614
Next, finding the average of the absorbances → 0.614 + 0.337 +0.363 = 0.438
Sample Calculation for finding Rate — (0.870M – Trial 1)
Equation : Change in absorbance/change in time = Rate
Work : 0.614/300 = 0.002 (absorbance s-1)
Uncertainty Calculations (Reference the table below at the bottom) :
●
Unaveraged Absorbance Uncertainty=(Initial Absorbance Uncertainty +Final Absorbance Uncertainty)
○ 0.870M Unaveraged Absorbance Uncertainty
■ The uncertainty on the initial and final absorbances are added, which is then applied to all the trials.(Reference the table below to view)
● 0.05+0.05 =0.1
●
Averaged Change in Absorbance Uncertainty= Largest absorbance – Smallest absorbance2
○ Average Change in Absorbance Uncertainty Calculation Sample — 0.870M
■ The largest change of absorbance is 0.614, which is then subtracted by the smallest change of absorbance value, 0.363 and divided by two.
●
0.614–0.3632
= 0.125
●
Unaveraged Rate Percentage=100 ×Trial Change in absorbance ± 0.1300 (Time) ± 0.5
○ 0.870M Trial 1 Percentage Uncertainty
■
0.614 ± 0.1300 ± 0.5
→
0.10.614
+
0.5300
= 0.863
×
100 = 8.23%
○ 0.870M Trial 2 Percentage Uncertainty
■
0.377 ± 0.1300 ± 0.5
→
0.10.377
+
0.5300
= 0.1335
×
100 = 13.35%
○ 0.870M Trial 3 Percentage Uncertainty
■
0.363 ± 0.1300 ± 0.5
→
0.10.363
+
0.5300
= 0.1386
×
100 = 13.86%
●
Averaged Rate Percentage = 100× Largest Rate Value – Smallest Rate Value2÷Average Rate
○ 0.870M Averaged Rate Law Uncertainty
■ (
0.002 – 0.0012×
100) = 0.0005
■
0.0050.001
= 50%
Trial 1
Trial 2
Trial 3
Averaged
Change in Absorbance
0.614±0.1
0.337±0.1
0.363±0.1
0.438 ± 0.125
Rate Law (absorbance s-1)
0.002 ± 8.23%
0.001±
13.35%
0.001±
13.86%
0.001 ±
50%
Qualitative Data
During all reactions, the reactants started off with tinted yellow, diluted for sodium hypochlorite and deep red, dime-size drops of red food coloring. As the reaction turned into a solution, the contents of the beaker turned into a dark, blue color at first, and then turned into an intense, yellow color a few seconds after swirling of the mixture. These characteristics were constant throughout all the concentrations.
Explanation of Measurement Uncertainty
The timer used on Logger Pro measured up to 300 seconds but since it only showed the number of seconds to the hundreds place, there is uncertainty within the decimals. There is also a large uncertainty in terms of the red food drops because the dropper that was embedded in the product was used; the red food drops were not measured in terms of how many grams were in each drop. Since there the absorbance kept changing, the time it took for it to be recognized and written down causes uncertainty of ±0.05.
Sample Graph
Graph Explanation:
Looking at the graphs, there seems to be a logarithmic decay function in the first order. Since the graph is first order, it confirms that as the concentration of bleach changes, the rate changes as well. Due to the fact that these graphs don’t have equations to show the line of best fit, it is difficult to conclude what the trend is. There could be some constants that contributed to the unreliability of the data such as the red food drops, an error in the functioning of the colorimeter, etc.
Calculated Graph:
Graph Explanation:
This graph does not reflect the expected trend and is therefore invalid due to the inconsistency with what the experiment should reflect. This graph is a cubic function with a rate that isn’t linear, which is what it should be. Ideally, the line would be straight because as the concentration is larger, the rate should be smaller because it would take a shorter time for the bleach to fully dissolve the red food coloring.
Conclusion & Evaluation
The data is not valid and does not show support of the theory that less diluted bleach should break down the red food coloring faster. The change in absorbance of each dilution is inconsistent and does not show a trend but otherwise, the graphs seem to all show the same specific shape. Due to the absence in the equations in relation to the graph, it is even more difficult to determine a valid conclusion. There could have been a constant human error that contributed to the data invalidity of this data such as a misreading of a reading or the colorimeter. Another big possibility is that the solutions in this experiment were used in such small quantities that it is easy for uncertainty to become very large with any minor changes. This ties in with the limitations of a colorimeter due to the fact that it only carries about 3.75 mL of solution. If this experiment could be replicated on a larger scale, it could show a clear trend and offer data for a valid conclusion. Furthermore, the uncertainty with regards to the red food drops is so big that it may have completely scattered the data, adding onto the small scale of the solution.
Error/Improvement:
Errors + Improvements
What is the error?
How it impacted the data
Possible Improvements
Inconsistency of time of transference (for volumetric flask to colorimeter cuvette)
The amount of time it took to stir the solution after the red food colorimeter and transfer it to the colorimeter is a human error because it could not be fully consistent. It could have caused a larger uncertainty on the initial absorbance because that value is always changing and and by the time the data had officially started, it could have taken longer to pour the solution in the cuvette.
Time the average amount of time it takes for the process of dropping the red food coloring → stirring → pouring into the cuvette → placing it in the colorimeter → starting the datalogger, and then average the times for each variation of data.
Colorimeter Usage
Colorimeters may be able to produce accurate color measurements, but they have many different flaws that may have contributed to the lack of trend in the data. One of the flaws is that the solution, being inside the colorimeter, is not unobservable. There is also quite some uncertainty in terms of identifying colorant strength and formation.
A Spectrophotometer would be an instrument that would be a significant improvement in comparison to a colorimeter. It is much more flexible and versatile than colorimeters, and they can measure metamerism, and identify colorant strength, analyze a comprehensive range of sample types. Spectrophotometers also provide full spectrum analysis that has much higher specificity, potentially identifying color differences missed by colorimeters.
Red Food Drops Uncertainty
Since there is such a big uncertainty regarding the drops that were used during the experiment, it could be an explanation of why the data showed no clear trend. The drops were not measured and could have been severely differentiated by the amount of pressure used to squeeze the drops out of the bottle.
Using a micropipette would permit the experimenter to be much more exact in the measurements. Micropipettes are much more precise than drops and would most likely result in a more clear trend in the data.
Extensions:
If this lab were to be repeated, a number of changes should be made. While this lab had strengths, such as the number of trials and the consistent environment where the experiment took place, it also had areas to be improved. Possible improvements for this experiment include using a larger quantity of each chemical with better equipment such as a spectrophotometer or a micropipette, and more trials for each concentration. This would allow for a more accurate value, as more trials average out to more accurate results, and more precise equipment with larger quantities of each chemical would allow for less uncertainty and a bigger possibility of a trend. A possible extension to this experiment would be to explore how sodium hypochlorite would act differently with various temperatures of bleach or with different colors of food coloring.
Work Cited
Brown, Catrin, and Mike Ford. Higher Level Chemistry. Pearson Education, 2014. Accessed 8 Feb. 2019.
Carter, Henry A. “Bleaches.” Chemistry: Foundations and Applications, edited by J. J. Lagowski, vol. 1, Macmillan Reference USA, 2004, pp. 123-129. Gale Virtual Reference Library, Accessed 8 Feb. 2019.
“Colorimetry.” Van Nostrand’s Encyclopedia of Chemistry, edited by Glenn D. Considine, 5th ed., Wiley-Interscience, 2005, p. 421. Gale Virtual Reference Library, Accessed 8 Feb. 2019.
Farr, James P., et al. “Bleaching Agents.” Van Nostrand’s Encyclopedia of Chemistry, edited by Glenn D. Considine, 5th ed., Wiley-Interscience, 2005, pp. 239-241. Gale Virtual Reference Library, Accessed 8 Feb. 2019.
Gregory, Peter. “Dye and Dye Intermediates.” Van Nostrand’s Encyclopedia of Chemistry, edited by Glenn D. Considine, 5th ed., Wiley-Interscience, 2005, pp. 512-516. Gale Virtual Reference Library, Accessed 8 Feb. 2019.
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