Chemistry IA PDF

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Chemistry IA...

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Topic: Determining ascorbic acid concentration of Vitamin Water when heated to different temperatures, 20°C, 40°C, 60°C, 80°C, and 100°C through a redox titration procedure using an iodine solution.

Research Question: What effect does altering temperature to 20°C, 40°C, 60°C, 80°C, and 100°C have on the ascorbic acid concentration of Vitamin Water?

Purpose: I’ve seen a few of my family members suffer from acute vitamin C deficiency, not to the point of scurvy, but enough so to show symptoms such as fatigue, unexpected weight gain, dry skin, and becoming prone to bruising. Generally, their physicians recommend tablets and drinks or fruit with a high concentration of vitamin C. My parents would visit them and bring cases of Vitamin Water and oranges. While I couldn’t figure out which type of Vitamin Water they drank, I thought it would be interesting to examine the effects of altering the temperature of the drink on its ascorbic acid concentration. Then, I could determine the optimal temperature to drink Vitamin Water at to maximize vitamin C intake. I chose to use the variety of Vitamin Water power-C dragon fruit because the dragon fruit is a dominant product of Vietnam’s, my home country’s, fruit exports.

Background information: Vitamin C, otherwise known as L-ascorbic acid, is an essential nutrient linked to major health benefits that is naturally present in a variety of foods, but is not synthesized endogenously by humans1. It is a water-soluble vitamin that plays a vital role in various aspects of human function, including protein metabolism and the biosynthesis of collagen. The recommended daily intake for an adult woman is 75 mg, whereas an adult man requires 90 mg. A major deficiency in vitamin C can lead to a disease called scurvy, causing abnormalities in the bones and teeth 2. In this experiment, we will be using a redox titration. There is another method to determine vitamin C concentration using DCPIP, but I have chosen to do a redox titration using an iodine solution because the endpoint is easier to identify. Titration is a laboratory method used to determine concentration of a substance, called an analyte 3. A redox titration takes the form of a reduction-oxidation reaction, where one species is reduced and the other is oxidized. In this case, the ascorbic acid will oxidize. As we are oxidizing, the formula under study is C6H8O6 + I3- + H2O → C6H6O6 + 3I- + 2H+

1

https://ods.od.nih.gov/factsheets/VitaminC-HealthProfessional/ https://www.thoughtco.com/vitamin-c-determination-by-iodine-titration-606322 3 https://www.britannica.com/science/titration#ref55414 2

Hypothesis: Alternative Hypothesis: Increasing the temperature will increase the degradation of ascorbic acid concentration in Vitamin Water. Null Hypothesis: There is no significant relationship between the ascorbic acid concentration and temperature in Vitamin Water.

Risk Assessment: Safety Issues: A lab coat, gloves, and safety goggles were worn at all times during this experiment. Long hair was tied back. Before turning the hotplate on, the cord was examined for damage. It was kept away from any volatile, flammable materials, monitored at all times, and was turned off once no longer needed. The 3 M sulphuric acid used is extremely corrosive and therefore capable of serious burns; it was handled with gloves and extreme care. The other chemicals used in this experiment pose little hazards but were also handled with care. Potassium iodine can stain skin and clothing. Ethical Issues: Solutions were neutralized before being poured down the sink to prevent groundwater contamination.

Apparatus and Materials: Table 1: List of apparatus and materials required for this experiment Name

Quantity

Uncertainty

Funnel

1

-

Burette and Stand

1

± 0.1 mL for burette

500 mL Volumetric Flask

2

± 5 mL

100 mL Volumetric Flask

1

± 0.1 mL

Transfer Pipette

1

-

100 mL Measuring Cylinder

1

± 0.1 mL

Thermometer

1

± 0.1 °C

250 mL Conical Flask

1

± 2.5 mL

125 mL Erlenmeyer Flask

25

± 2.5 mL

Scale

1

± 0.01 g

10 mL Measuring Cylinder

1

± 0.01 mL

Potassium Iodide (KI)

5.0 g

-

Potassium Iodate (KIO3)

0.268 g

-

Distilled Water

1020 mL

-

Ascorbic Acid

0.250 g

-

Tap Water

50 mL

-

Soluble Starch

0.25 g

-

Water

50 mL

-

3 M Sulphuric Acid

30 mL

-

Method: 1. Creating Iodine Solution: a. Weigh 5.0 g of potassium iodide and 0.268 g of potassium iodate and dissolve into 200 mL of distilled water b. Add 30 mL of 3 M sulphuric acid c. Dilute to a final volume of 500 mL using distilled water d. Swirl until iodine is dissolved. e. Move into 1 L beaker and fill with distilled water up to 1 L mark. f. Label as iodine solution. 2. Creating 1% Starch Indicator Solution: a. Add 0.25 g of soluble starch to 50 mL of near boiling water in a 250 mL conical flask. b. Stir to dissolve starch and cool before use. c. Label as starch indicator solution. 3. Creating Vitamin C Standard Solution a. Measure 0.250 g of ascorbic acid and dissolve into 100 mL of distilled water in a 500 mL volumetric flask. b. Measure out 150 mL of distilled water in another 500 mL volumetric flask and add to volumetric flask in previous step. c. Label as vitamin C standard solution. 4. Preparing Burette and Stand a. Rinse the burette, including the tip, with distilled water.

b. Rinse the burette twice with 10 mL aliquots of the potassium iodine solution. Swirl to ensure all surfaces are covered. c. Mount the buret on the stand using the ring clamp as depicted in Figure 1 below. 5. Standardizing Solutions a. Add 25 mL of the vitamin C standard solution and 10 drops of the 1% starch solution into a 125 mL Erlenmeyer flask. b. Fill burette with iodine solution and record the initial volume (just below 0.00 mL mark works) using the funnel. c. Open the burette tip and mark the degree of opening to ensure it is the same for following trials. Doing so will produce more accurate results. d. Swirl flask at a constant rate. Titrate until endpoint is reached. This will be identified as a blue colour remaining for at least 20 seconds. Stop the titration process by closing the tip as soon as this point is reached. e. Record the final volume. Calculate the volume required by subtracting the final volume from the initial volume. f. Repeat titration two more times and ensure results agree within 0.1 mL. 6. Titrating Vitamin Water a. Heat up 25 mL of Vitamin Water to 20 °C in a 125 mL Erlenmeyer flask on a hot plate. b. Add 10 drops of the 1% starch solution. Place under burette. c. Fill burette with iodine solution using the funnel and record initial volume. d. Open the burette tip to the degree of opening previously marked when standardizing solutions. e. Swirl flask at a constant rate until endpoint is reached. This will be identified as a dark black-blue colour persisting longer than 20 seconds. Stop the titration process by closing the tip as soon as this point is reached. f. Record the final volume. Calculate the amount of solution required for titration to complete by subtracting the final volume from the initial volume. g. Repeat five times. h. Repeat steps 6 a-g but heat the initial 25 mL of Vitamin Water to temperatures of 40°C, 60°C, 80°C, and 100°C. Perform five trials of solutions at each temperature.

Figure 1. Setup of burette and flask4.

Variables: Table 1: Independent Variable Variable

How variable was changed

Significance of changing variable

Temperature of Vitamin Water solution

Heated to different temperatures using a hot plate

Changing the this variable will allow us to examine how the concentration of vitamin C in Vitamin Water is affected by temperature changes.

Table 2: Dependent Variable Variable

Why variable will change

Vitamin C concentration of Vitamin Water solution

The temperature to which the Vitamin Water solution is heated to will present an effect on its vitamin C concentration.

Table 3: Control Variables

4

Variable

How variable was controlled

Significance of controlling variable

Variety of Vitamin Water

All trials used Vitamin Water power-C dragon fruit.

Using different varieties of Vitamin Water will produce inaccurate results because they will have varying concentrations of vitamin C,

http://kidskunst.info/15/02796-titration-setup.htm

independent of temperature. Light intensity present in lab

All trials were conducted on the same day and in the same lab, with the light intensity remaining constant. They were conducted in the same area, taking into account the light coming in from windows.

Titrating the Vitamin Water solutions required determining endpoint using eyesight. Different light intensities present in the lab would cause the solution to appear darker/lighter and therefore affect how much solution was titrated.

Source and batch of Vitamin Water

All Vitamin Water used in this experiment was sourced from the same bottle.

Different batches or bottles of Vitamin Water could contain different concentrations of vitamin C and therefore skew the results.

Rate of iodine solution added

Iodine solution was added at a constant rate by marking the degree of opening on the burette so that each trial would have it open the same amount.

The redox reaction requires time to occur before results can be seen. Adding the solution too quickly means that it has less time to react and too much solution would be added.

Rate of swirling during titration

Flask was swirled manually at Swirling during titration a steady rate. However, this increases the rate of reaction is still inaccurate and a due to the increase of the magnetic stirrer would kinetic energy of the particles. produce more reliable results. Swirling the solutions at different rates would allow the reaction to occur faster or slower and therefore skew the amount of iodine solution required.

Quantitative Data: Table 4: Vitamin C standard solution titration results Initial reading of iodine solution in burette (± 0.1 mL)

Final reading of iodine solution in burette (± 0.1 mL

Titre of iodine solution (± 0.1 mL)

0.00

10.4

10.4

10.4

20.7

10.3

20.7

31.0

10.3

Average titre of trials (± 0.1 mL)

10.3

Table 5: Data showing the volume of iodine solution required to titrate Vitamin Water at different temperatures Temperature to which Vitamin Water was heated (±0.1°C)

20

40

Initial reading of iodine solution in burette (± 0.1 mL)

Final reading of iodine solution in burette (± 0.1 mL)

Titre of iodine solution (± 0.1 mL)

0.00

4.9

4.9

4.9

9.0

5.1

9.0

14.1

5.1

2.3

7.7

5.4

7.7

13.0

5.3

0.00

4.5

4.5

4.5

9.2

4.7

9.2

13.4

4.2

13.4

18.4

5.0

18.4

23.8

5.4

23.8

27.9

4.1

27.9

32.4

4.5

Average of titres of all trials (± 0.1 mL)

Standard deviation (± 0.1 mL)

5.2

0.2

4.8

0.4

60

80

100

4.5

8.4

3.9

8.4

12.3

3.9

12.3

16.6

4.3

8.7

12.3

3.6

12.3

16.4

4.1

16.4

21.1

4.7

21.1

25.2

4.1

25.2

29.1

3.9

0.00

3.9

3.9

3.9

8.1

4.2

8.1

12.2

4.1

12.2

16.1

3.9

16.1

20.0

3.9

4.1

0.2

4.1

0.4

4.0

0.1

Using data from the first five trials conducted (solution heated to 20°C): Example calculation of standard deviation: 2

σ=

(4.9−5.2)

2

2

2

2

+(5.1−5.2) +(5.1−5.2) +(5.4−5.2) +(5.3−5.2) 5

= 0.1743559 = 0.2 mL

Example calculation of average of titres: Average =

4.9+5.1+5.1+5.4+5.4+5.3 = 5

5.16 mL

Processed Data: The following calculations were made to determine the amount of Vitamin C present in the solutions by first determining the average titre of iodine solution for the vitamin C standard solution (shown above in table 4) = 10.3. Table 6: Processed data after calculations to determine mass of vitamin C present Temperature to which Vitamin Water was heated (±0.1°C)

Average mass of vitamin C present

20

0.13

40

0.12

60

0.10

80

0.10

100

0.09

Using data from tables 4-6 where the Vitamin Water was heated to 20°C: a) Example calculation of average mass of vitamin C present: Using the data from the standard solution titration, I can determine a ratio that will allow me to determine the concentrations of my Vitamin Water trials: 10.3 𝑚𝐿 𝑖𝑜𝑑𝑖𝑛𝑒 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 0.250 𝑔 𝑎𝑠𝑐𝑜𝑟𝑏𝑖𝑐 𝑎𝑐𝑖𝑑

=

5.2 𝑚𝐿 𝑖𝑜𝑑𝑖𝑛𝑒 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 𝑥 𝑚𝐿 𝑎𝑠𝑐𝑜𝑟𝑏𝑖𝑐 𝑎𝑐𝑖𝑑

x = 0.13 = amount of vitamin C present in that sample Two decimal places are used because the scale used in this experiment was accurate up to two decimal places Data was processed for the average titre to limit inaccuracies rather than each individual trial to limit the amount of times the data was processed and therefore maintain maximum accuracy.

Graph:

Figure 2. Chart showing the relation between the mass of vitamin C in Vitamin Water and the temperature to which it is heated to

Using this data, I created a graph showing the negative correlation between the mass of vitamin C present in Vitamin Water and the temperature to which it is heated to. The error bars represent 2 standard errors calculated above.

Evaluation and Conclusion: Table: Weaknesses and suggestions for improvement Weakness

Significance(s) of weakness

Suggestion(s) for improvement

Swirling of beaker during titration was not consistent throughout all trials. Due to this being done manually, it was subject to human error.

Inconsistent movements will produce inconsistent results because the swirling controls the rate of the reaction. Swirling the beaker faster will increase the rate of the reaction and allow less iodine solution to be titrated in. Swirling it slower will decrease the rate of reaction and more iodine will be titrated in than required.

Using a magnetic stirrer would be the best way to ensure the swirling is consistent throughout all trials and this would produce more reliable results.

Only one variety of Vitamin Water was used.

The results of this experiment cannot be generalized to all kinds of Vitamin Water.

Increase the variety of Vitamin Water experimented on. I used a variety that was specifically high in Vitamin C, so it would be interesting to use one that is specifically high in other minerals or vitamins. The concentrations of different vitamins could also be tested as a way to expand this experiment.

Low number of trials

Having a low number of trials makes the experiment susceptible to anomalies and errors that limit the reliability of the experiment.

Holding more trials will minimize the risk of errors. Anomalies will be easier to identify and exclude.

Airborne contaminants into the flask during titration

Bacterial contaminants can limit the reliability of the experiment by skewing the results.

While this weakness cannot be completely avoided, its effect can be limited by eliminating all wind sources present in the lab, such as windows, air conditioners or heaters. I also conducted this experiment with other students in the lab, who may have stirred up dust when moving around the room. Being the only person present in the lab during the experiment would limit this weakness.

Difficulty determining endpoint of titration. As this is determined purely by eyesight, it is subject to human error.

The difficulty with A colorimeter could more determining endpoint accurately determine manually through eyesight is endpoint. being presented with the issue of interpretation. The interpretation of the endpoint could be different with each individual.

Oxidation of ascorbic acid through exposure to light and air

The oxidation process could have been sped up by the presence of light or air, thus limiting the reliability of the investigation.

Limit the amount of light and air travelling through the lab. Close any windows and turn off air conditioning and heating.

This exploration aimed to determine the optimal temperature to drink Vitamin Water at to maximize vitamin C intake. This was done through a redox titration using an iodine solution. I titrated Vitamin Water at different temperatures of 20°C, 40°C, 60°C, 80 °C, and 100 C to determine the vitamin C concentration at each stage. The vitamin C content present in drinks and food is proportionate to the temperature they are stored at because of oxidation. This can be seen in the equation: 2 ascorbic acid + O₂⇌ 2 dehydroascorbate + 2 H₂O As we are experimenting with a redox titration using an iodide solution, the formation of dehydroascorbate is formed by oxidizing vitamin C and the formula under study is: C6H8O6 + I3- + H2O → C6H6O6 + 3I- + 2H+ My quantitative data showed that an increase in temperature led to an increase in the amount of iodine solution required to reach the endpoint of the titration. This means the vitamin C content

has decreased, and therefore, my null hypothesis can be accepted. I calculated the amount of vitamin C present in each trial in grams using the titration data, taking standard errors into account. I then created a visual graph and table to more easily view any patterns that could appear. Following the 60 °C mark, we can see that there is much less significant change in the concentrations. In figure 2, we can see that the graph is not linear; the drop between 20°C and 40°C is the most prominent. This could be due to the presence of the enzyme L-ascorbate oxidase, responsible for the catalyzation of vitamin C. After exceeding its optimal temperature, it denatures and the hydroxyl bonds in the ascorbic acids subsequently break. At the most optimal temperature of the f...