How does temperature affect the concentration of vitamin C in orange juice?
Osmosis is a type of passive transport and also the movement of water across a semipermeable membrane. The water molecules move from a higher water potential environment to a lower water potential environment. In osmosis, there are three types of solutions that are used to describe the water movement. The first is the hypertonic solution which has a higher solute concentration.
Vitamin C (also known as ascorbic acid) ) is abundant in vegetables and fruits. A water- soluble vitamin and powerful antioxidant, it helps the body form and maintain connective tissue, including bones, blood vessels, and skin. (Vitamin C Benefits, 2016)
Ascorbic acid is a six-carbon compound related to glucose (C6H8O6). It is found naturally in citrus fruits and many vegetables. Ascorbic acid is an essential nutrient in human diets, and necessary to maintain connective tissue and bone.(PubChem, 2011) Vitamin C helps to repair and regenerate tissues, protect against heart disease, aid in the absorption of iron, prevent scurvy, and decrease total and LDL (“bad”) cholesterol and triglycerides. (Vitamin C Benefits, 2016) (Picture from PubChem)
The thermal stability of vitamin C (including l-ascorbic acid [l-AA] and dehydroascorbic acid [DHAA]) in crushed broccoli was evaluated in the temperature range of 30 to 90 degrees C Figure 1: Structure of Vitamin C whereas that of ascorbic acid oxidase (AAO) was evaluated in the temperature range of 20 to 95 degrees C. (NCBI, 2010)
Oranges have the highest amount of vitamin C among citrus fruits. A medium whole orange contains around 70 milligrams of vitamin C. Orange juice is a concentrated source of vitamin C because it removes the rind and most of the pulp, which are not as high in the vitamin. An 8-ounce glass of 100 percent orange juice provides up to 125 milligrams of vitamin C (Livestrong.com, 2013)
Factors that influence concentration of vitamin C
The oxidation of ascorbic acid can be slowed down / prevented if there is no oxidiser present. In other words, a molecule has to be presented that will receive the electrons
2. Metal ions
Metal ions are also good in participating in oxidation and its opposite, reduction reactions. In the case of ascorbic acid, metal ions can catalyse the reaction
3. pH of the orange juice
For a lot of reactions, the pH influences the reaction speed. For reactions that involve an acidic or alkaline component, that is especially important
Temperature determines the movement of molecules in food. The higher the temperature, the more atoms and molecules to meet one another and thus react. Therefore, a higher temperature often results in a higher reaction rate (Food Chemistry, 2016)
Oxidation is a reaction in which electrons are lost to another species. It is when oxygen molecules react with all different substances that they contact, can be from metal to living tissue. With the discovery of electrons, oxidation was defined as the loss of at least one electron when two or more substances react.
Reduction is essentially the opposite of oxidation it is any reaction always occur when an oxidation reaction does. Reduction is a chemical reaction that involves the gaining of electrons by one of the atoms involved in the reaction
In this experimental investigation, the technique of Redox Titration is used to determine the concentration of Ascorbic acid in orange juice. Together, reduction and oxidation form redox reactions (reduction-oxidation = redox). A redox titration is a type of titration based on a redox reaction between the analyte and titrant. Redox titration may involve the use of a redox indicator and/or a potentiometer. A common example of a redox titration is treating a solution of iodine with a reducing agent to produce iodide using a starch indicator to help detect the endpoint. (Wikipedia, 2016) Also, at higher temperatures, since the molecules are moving faster, they collide with greater energy. That means more molecules will collide with an energy that is greater than the activation energy so that more of the collisions will result in a reaction. (Organic Chemistry, 2016) Redox Titration is different from the Acid- Base Titration. In an acid- base titration, the species involved are acids and bases while redox titrations are titrations that take place among redox species. (PEDIAA, 2015) The redox reaction is better than an acid-base titration since there are additional acids in a juice, but few of them interfere with the oxidation of ascorbic acid by iodine. (ThoughtCo., 2017)
Collision Theory provides a qualitative explanation of chemical reactions and the rates at which they occur. A basic principal of collision theory is that, in order to react, molecules must collide. This fundamental rule guides any analysis of an ordinary reaction mechanism. (Boundless, 2016) Increasing the temperature increases the rate of a reaction because, as the temperature increases, the reactant molecules move faster and are more likely to collide with each other. More collisions mean that the rate of reaction will increase.
Oxidation is gain of electrons. Reduction is loss of electrons. They usually happen simultaneously. When the Vitamin C is oxidated, two hydrogen atoms are reduced and form Dehydroascorbic acid. As oxidation and reduction will occur at the same time, the first equation will be the first half, then the second equation will be the reduction.
Iodine => Iodide
Equation 2 shows the second half of the reaction which is the reduction.
In the experiment, starch indicator solution is added to the orange juice to observe the effect of titration. When the ascorbic acid in the juice finishes reacting or oxidating (equation 1), the reduction of Iodine begins and transforms into iodide (equation 2). This then indicate the end and complete of the Redox titration.
Iodate ion+ iodide ion+ acid => Iodine
Equation 3 shows that all the chemicals and solutions are involved in the experiment before titration. Potassium Iodate is , Potassium Iodide is KI and Hydrochloric acid is HCl. The ratio of Iodate ion and ascorbic acid is also shown in this equation which it is 1 to 3. This ratio will be beneficial for the calculation of moles of ascorbic acid in analysis part
This equation is the combination and ultimate version of equation 3 and 4. It is also a picture shows the whole experiment, which when ascorbic acid has used up the iodine then it will turn into with iodide. This is called the endpoint of the titration.
– Independent variable: Temperature of orange juice (25, 35, 45, 55, 65 Degree Celsius)
25 Degree Celsius is selected for the least temperature for the investigation because it is the room temperature and produces obvious result which is easy to record and reach this temperature. 65 Degree Celsius is selected to be the highest temperature because a too high temperature will decompose the Vitamin C and evaporate some of the orange juice. 10 Degree Celsius is also selected to be the regular interval, in order to have a notable change of effect on concentration (Too less-produces merely little differences.)
– Dependent variable: Amount of potassium iodate in titration with orange juice (vitamin C)
In the experiment, the initial and final volume in titration will be recorded. With the mathematical subtraction, the amount of volume used of Potassium Iodate will be obtained.
– Controlled variables:
i) Brand of Orange Juice
Golden Circle is chosen to be the brand of orange juice in this experiment and it contains 40mg of Vitamin C. This factor is important since different brands and kinds of orange juice contain different amount of vitamin C which is the thing that are testing in this experiment. Therefore, the orange juice used should be the same bottle throughout the investigation
ii) Volume of orange juice for titration
The volume of orange juice involved in the experiment is to be 20ML as set. The ascorbic acid is varied by the volume of orange juice. Therefore, the exact volume of 20ML should be ensured in the experiment to make the result even.
iii) Amount of Starch indicator solution, Potassium Iodide solution and Dilute hydrochloric acid
Both Potassium Iodide solution and Dilute hydrochloric acid must be 5ml each and starch indicator with 3 drops. All of them are to be same in the investigation so the result obtaining will not be varied and create great errors.
iv) Room temperature
The room temperature should always stay at about 25 to 26 Degree Celsius so that loss of heat of orange juice will not be varied. Air conditioner should be turned in order to maintain the temperature. The first one will be the temperature affect most if this factor isn’t stable.
v) Heating the orange juice in a certain time
The orange juice is planned to heat up with 15 minutes so it can be stable. The heating time should all be the same so the temperature will not be varied because of the residual heat after heating.
vi) Concentration of Potassium Iodate
The concentration of Potassium Iodate is confirmed to be 0.002M. The concentration of this solution should be constant for every trial so the results can be fair and accurate.
As the temperature increases, the concentration of vitamin C will decrease. As a result, smaller amount of potassium iodate will be involved.
Temperature increases the rate of oxidation because the molecules are moving around faster and having more collisions, so there are more opportunities for the reaction to occur.
Collision theory states that the rate of a chemical reaction is proportional to the number of collisions between reactant molecules. The more often reactant molecules collide, the more often they react with one another, and the faster the reaction rate. (Kinetic and Collision theory)
For a reaction to happen, reactant particles must collide with enough energy for the collision to be successful. The rate of reaction increases if there is an increase in temperature, concentration of reactants in solution or pressure of gaseous reactants. These changes can be explained in terms of the rate of successful collisions. (GCSE)
The chemical instability of vitamin C acid is due to the fact that it is a strong reducing agent and can be deactivated by a wide range of oxidizing agents. a negative impact over the preservation of vitamin C content alongside raw materials conversion into the final products. (SCIENTIFIC STUDY & RESEARCH, 2008)
With higher temperature and reaction rate, the volume of Potassium Iodate needed is lesser to reach to the endpoint of titration.
Table 1: Dangers and way to prevent in the experiment
Materials and Apparatus
- 4 x 250mL beakers
- 1 x Hot plate
- 1 x Funnel
- 1 x burette
- 1 x stand
- 1 x 250mL conical flask
- 1 x 10mL/ 20mL pipette
- 1 x 2L bottle of orange juice
- 1 x cling wrap
- 1 x thermometer
- 1 x 150mL conical flask
- 1 x pipette
- Starch indicator solution (3 drops for each trial)
- Potassium Iodide solution (0.6M)
- Dilute hydrochloric acid (1M)
- Potassium Iodate solution (0.02M)
Modification of procedure
- Cling wrap was not involved in the experiment
- Due to the safety reason of avoiding it to get melt by high temperature
- The orange juice didn’t heat up for 15 minutes instead, 20minutes
- Hot plate was not hot enough
- Heat was lost to the surrounding
Table 2: Result of heating orange juice at 25 ℃
Table 3: Result of heating orange juice at 35 ℃
Table 4: Result of heating orange juice at 45 ℃
Table 5: Result of heating orange juice at 55 ℃
Table 6: Resulting of heating orange juice at 65 Degree Celsius
- The first trial (pilot) in every temperature has generally higher volume used than the other three other actual trials because it was a testing to see the colour.
- The colour of orange juice is orange before Redox titration, but after that, the colour of result should be dark green
- Amount of starch solution involved has a great impact on the result. It has to be 3 drops or a standard amount
- Over- titration will lead to the result colour be dark blue colour
- Vitamin C and some of the orange juice on the surface at the top will evaporate due to a high temperature
- Some trials of 25 Degree Celsius have redone due to the mishandling of solution, which 5ml of starch solution are poured into the flask instead of 3 drops which greatly affect the result and errors are made.
In the experiment, 4 trials are gone through and 3 trials are the actual ones. In order to get a fair and precise result, an average number of volume used is calculated for each temperature.
Table 7: Average volumed used in all temperature
Table 8: Residue Error for different temperature in titration
Concentration of ascorbic acid can be calculated with the values obtained from the volume used in titration.
25°C Begin with calculating the average volume for the particular temperature
Convert millilitres to litres so the moles of potassium iodate can be calculated
Since the concentration of potassium iodate is known as 0.002, therefore
A mole ratio can be obtained from a balanced equation, and the mole ratio between IO3– and ascorbic acid is 1: 3.
In the experiment, 20mL of orange juice is tested for each trial. Therefore, the volume of ascorbic acid is 20mL = 0.02L.
Concentration of ascorbic acid
Table 9: Concentration of Ascorbic acid in average volume of potassium iodate
Sample calculation: To get the concentration of largest error
Table 10: Residual Errors in concentration of Ascorbic Acid
Graph 1: Concentration of Vitamin C calculated by volume used of potassium iodate in different temperature
For Concentration for 25 Degree Celsius and 35 Degree Celsius:
For Concentration for 45 and 55 Degree Celsius:
The aim of this experimental investigation is to investigate and explore the effect of different temperatures on concentration of vitamin C in orange juice. It is hypothesised that as the temperature increases, the amount of potassium iodate involved will be smaller, and as a result, the concentration of vitamin C will decrease with the increasing temperature. The result has shown that the hypothesis is supported which the volume of Potassium Iodate needs is less.
The result is shown to be supported in the data in Table 9 and Graph 1. In table 9, the concentrations calculated from 25°C to 65°C have a trend of reducing molarity when increasing the temperature involved in the Vitamin C. 25°C has the value of 3.81 x 10-4 whereas 65°C has 8.1 x 10-5. In Graph 1, a falling trend line and pattern is formed and with a collinear equation that can only be barely seen the difference. It also portraits the inverse relationship between the temperature and concentration of ascorbic acid to indicate the existence of Collision theory in this investigation. The Collision theory is the principle behind this experiment. It states that reaction rate is affected by the particles and high temperature results in high reaction rate. In the Redox titration, when the ascorbic acid is heated up, the rate of reaction of the solution will be higher. Therefore, the volume of potassium Iodate needed is lesser. the molecules go around in their structure a lot more when the temperature is higher due to have more energy. It will also be more likely to collide and means they are also more likely to combine. (Chem4Kid)
Slopes for 4 of the value (2 lines) are calculated to show whether they are fitted into the actual overall slope. The equation obtained from Excels is y = -0.069x + 5.169, it indicates the concentration shows reliability by having the close number. Both the slope has a falling rate of change and support the trend line by staying in correct positions in the line.
Errors were made throughout the experiment but consistency is also shown. Table 2 to 6 are raw data of Redox Titration experiment and provide the original information to further analyse. As a result, the raw data is the one of the key to determine accuracy. The most consistent set of result is data from Table 3, the result of heating orange juice at 35°C whereas the least consistent set of result is data from Table 4 for 45°C. Inconsistency was due to the heat lost to the surrounding before experiment began, and they are led by the temperature difference to room temperature. Improper handlings of the solution and cling wrap were also other reasons to lack of overall accuracy. However, the errors only have a little impact on the result since they are not that large.
Limitations were made throughout the experiment and they can be shown in the tables at the front. Firstly, determining the colour of the endpoint of titration is subjective and they can look different every time. This was the problem of misjudging colour. This results in errors of the volume used in KIO3 and eventually lead to the error of calculating concentration of Ascorbic Acid. Secondly, in Table 7, the greatest residual error made is ±0.2mL. This can be possibly due to the accuracy of measurement equipment. It also affects the result recording at the end of the experiment. Moreover, the ascorbic acid in the orange juice has oxidated which makes the experiment produced some errors. Human Error and apparatus are the main factor of not having a perfect result.
Improvements can be made in this investigation. In the experiment, instructions are well followed and only little errors are produced. However, they should also be avoided by making some changes in procedure. The biggest problem in this work was the reading of volume on the burette. Since it is a group work, we should let everyone in the group to read it and make an agreement so the result will not be subjective. Also, to avoid the parallax errors, a good position for reading should be chosen properly. In addition, the accuracy of pipette and measuring cylinders should be ensure which the measuring interval shown on them should be more and have a smaller scale to obtain a better result. Lastly, in the experiment, trials after trials, the flasks were washed up. After the rinsing, no water should be left in it. This is because the contaminated beaker will make that the volume used of KIO3 lesser and affect the calculation of concentration of Ascorbic Acid.
The experiment is hypothesised that higher temperature of ascorbic acid results in lesser Potassium Iodate to titrate it. The results support the hypothesis and also indicate that high reaction rate will lower the concentration of ascorbic acid. Results are represented in tables and graphs to determine the accuracy for them. A trend line is drawn for the concentration of Vitamin C in graph 1 and shows that the R2 has the number of 0.9296 (where R2 represents perfect) and a collinear equation. This investigation shows successful and reliable result to the Collision theory behind and the hypothesis. Nevertheless, errors are made due to human errors and apparatus but only a small effect results are made. Improvements like avoiding the parallax error and precision of equipment will obtain a better result.
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