Discussion Examples for Iodine Value of Fats and Oils | Degree of Unsaturation and Susceptibility to Oxidation

What Is the Iodine Value of Fats and Oils?

The iodine value is a value representing the number of grams of iodine that add to 100 g of fat or oil.
Unsaturated fatty acids in fats and oils contain carbon-carbon double bonds, and iodine and other halogens add to these double bonds.
Therefore, the higher the iodine value, the more unsaturated bonds are considered to be present in the fat or oil.

The iodine value is an indicator used to evaluate the degree of unsaturation of fats and oils.
It tends to be high in vegetable oils and fish oils containing large amounts of unsaturated fatty acids and low in fats and oils containing large amounts of saturated fatty acids.
It is an important value when considering the properties, oxidative stability, and drying characteristics of fats and oils.

Main Items to Include in the Results

In the results of iodine-value measurement, organize the type of fat or oil sample, sample amount, type and amount of reaction reagent added, reaction time, reaction conditions in the dark, addition of potassium iodide, concentration of the sodium thiosulfate standard solution, blank titration volume, sample titration volume, iodine value, and other information.
Because the amount of iodine added to the fat or oil is determined from the difference from the blank test, the blank-test value is important.

Main Items to Include in the Results

• Type of fat or oil sample
• Mass of the fat or oil sample
• Type of reaction reagent
• Amount of reaction reagent added
• Reaction time
• Whether the reaction was carried out in the dark
• Amount of potassium iodide added
• Concentration of the sodium thiosulfate standard solution
• Blank titration volume
• Sample titration volume
• Difference from the blank test
• Timing of addition of the starch indicator
• Color change at the endpoint
• Iodine value
• Average value from multiple measurements
• Comparison with literature values and other fats and oils
• Causes of error and points for improvement

Reference Experimental Values and Calculation Examples for Iodine-Value Measurement

Here, for iodine value, an indicator of the degree of unsaturation of fats and oils, titration volumes, differences from the blank, calculation of iodine value, differences among types of oils, and the relationship with susceptibility to oxidation are organized using reference experimental values.

The iodine value is a value expressing in grams the amount of iodine that adds to 100 g of fat or oil.
The more double bonds a fat or oil contains, the more iodine adds, resulting in a larger iodine value.
Therefore, iodine value can be used as an indicator for comparing the degree of unsaturation of fats and oils.

Reference Experimental Conditions

Concept of Iodine-Value Measurement

When a reagent containing iodine is added to fats and oils, iodine adds to the carbon-carbon double bonds in the fats and oils.
The iodine remaining after the reaction is titrated with sodium thiosulfate, and the amount of iodine that added to the fat or oil is determined from the difference from the blank.

Titration Results for Different Types of Oil

Reference examples are shown for iodine-value measurements of different types of fats and oils under the same conditions.
The blank titration volume is assumed to be 25.60 mL, and the sample mass is 0.200 g in all cases.

Example Calculation of the Difference From the Blank

The amount of iodine that added to the fat or oil corresponds to the difference between the blank titration volume and the sample titration volume.

Difference from blank = Blank titration volume − Sample titration volume

For soybean oil, the blank titration volume is 25.60 mL and the sample titration volume is 5.65 mL.

Difference from blank = 25.60 − 5.65 = 19.95 mL

The larger this difference, the more iodine the fat or oil consumed, indicating that more double bonds are considered to be present.

Example Calculation of Iodine Value

The iodine value can be determined using the following equation.

Iodine value = (Blank titration volume − Sample titration volume) × Sodium thiosulfate concentration × 12.69 ÷ Sample mass

Here, the titration volume is expressed in mL, the concentration in mol/L, and the sample mass in g.
For soybean oil, the difference from the blank is 19.95 mL, the sodium thiosulfate concentration is 0.100 mol/L, and the sample mass is 0.200 g.

Iodine value = 19.95 × 0.100 × 12.69 ÷ 0.200

Iodine value = 126.7

Therefore, in this reference example, the iodine value of soybean oil is determined to be 126.7.

Comparison of Iodine Value and Degree of Unsaturation

Oils with higher iodine values are considered to contain more double bonds.
Therefore, iodine value can be used as a guide for comparing the degree of unsaturation of fats and oils.

In this reference example, coconut oil had the lowest iodine value and fish oil had the highest iodine value.
Fish oil contains large amounts of highly unsaturated fatty acids with many double bonds, which is considered to be why its iodine value was high.

Changes in Iodine Value During Storage

When fats and oils are oxidized, double bonds may react with oxygen and decrease.
Therefore, iodine value may decrease in oils in which oxidation has progressed.

The iodine value decreased more under harsher storage conditions.
This was considered to result from double bonds in the fats and oils being consumed in oxidation reactions, thereby decreasing the degree of unsaturation.

Relationship With Peroxide Value

Iodine value is an indicator of the degree of unsaturation, while peroxide value is an indicator of the amount of early oxidation products.
Comparing both makes it easier to separately consider whether a fat or oil has a structure that is susceptible to oxidation and whether oxidation has actually progressed.

Oils with higher iodine values tended to show higher peroxide values after storage.
This is considered to result from oils containing more double bonds being more susceptible to oxidation reactions.

Example Calculation of the Percentage Decrease in Iodine Value Due to Oxidation

Comparing iodine values before and after storage makes it possible to evaluate how much the degree of unsaturation changed because of oxidation.

Percentage decrease in iodine value (%) = (Iodine value before storage − Iodine value after storage) ÷ Iodine value before storage × 100

When soybean oil was opened and left standing, the iodine value before storage was 126.7 and the iodine value after storage was 112.6.

Percentage decrease = (126.7 − 112.6) ÷ 126.7 × 100 = 11.1%

From this result, part of the double bonds was considered to have been oxidized by leaving the oil open, causing the iodine value to decrease by approximately 11.1%.

Example When the Measured Values Vary

In iodine-value measurement, the measured values may vary depending on reaction time, light protection, titration endpoint, and sample weighing.
The following shows an example in which the same soybean oil was measured three times.

The three measured values ranged from 126.2 to 127.0 and agreed relatively well.
Reducing errors in endpoint determination and sample mass makes it easier to obtain reproducible values.

Example of How to Write the Results

When the iodine values of various fats and oils were measured, the values were 10.5 for coconut oil, 80.3 for olive oil, 111.1 for canola oil, 126.7 for soybean oil, and 157.5 for fish oil.
From these results, coconut oil was considered to have a low degree of unsaturation, while fish oil was considered to have a very high degree of unsaturation.

For soybean oil, the sample titration volume was 5.65 mL compared with a blank titration volume of 25.60 mL, giving a difference of 19.95 mL.
Using a 0.100 mol/L sodium thiosulfate standard solution and a sample mass of 0.200 g, the iodine value was calculated to be 126.7.

In addition, when soybean oil was stored for 14 days, the iodine value was 123.8 under room-temperature dark storage, 118.5 under light exposure, 114.2 after storage at 40°C, and 112.6 when opened and left standing.
The iodine value decreased more under harsher storage conditions, suggesting that double bonds in the fats and oils may have decreased because of oxidation.

Points for Connecting the Results to the Discussion

In a discussion of iodine value, it is useful to relate the magnitude of the value to the degree of unsaturation of the fat or oil and further explain susceptibility to oxidation and changes caused by storage conditions.

• Has the difference between the blank titration volume and sample titration volume been correctly determined?
• Can it be explained that oils with higher iodine values contain more double bonds?
• Can the reason iodine values differ among types of fats and oils be explained in relation to fatty-acid composition?
• Can it be explained that oils with higher iodine values tend to be more susceptible to oxidation?
• Can the reason the iodine value decreased after storage be explained in relation to oxidation of double bonds?
• Can the degree of unsaturation and oxidative deterioration be discussed separately by comparison with peroxide value?
• Can reaction time, light protection, titration endpoint, and errors in sample mass be discussed as factors affecting the measured values?

Example Discussion

In this experiment, iodine values were measured for several types of fats and oils and their degrees of unsaturation were compared.
The iodine value of coconut oil was low at 10.5, while that of fish oil was high at 157.5.
Because iodine value indicates the amount of iodine that adds to 100 g of fat or oil, a higher value indicates that more double bonds are present.
Therefore, fish oil was judged to have the highest degree of unsaturation among the fats and oils measured in this experiment.

The iodine value of soybean oil was 126.7, which was higher than the value of 80.3 for olive oil.
This was considered to result from soybean oil containing relatively large amounts of polyunsaturated fatty acids, whereas olive oil mainly contains monounsaturated fatty acids.
Because fats and oils with more double bonds add more iodine, the higher iodine value can be explained.

In soybean oil stored under different conditions, the iodine value decreased greatly when the oil was opened and left standing or stored at 40°C.
This was considered to result from the double bonds in the fats and oils being oxidized under the influence of oxygen in the air and heat, reducing the number of double bonds capable of adding iodine.
In particular, the oil left open was more readily exposed to oxygen and was therefore considered to have undergone oxidation more readily.

In addition, oils with higher iodine values tended to show higher peroxide values after storage.
This is because oils with higher degrees of unsaturation are more susceptible to oxidation reactions and more readily generate peroxides.
However, iodine value is an indicator of the degree of unsaturation, whereas peroxide value is an indicator of early oxidation products, so the two must be distinguished when evaluating deterioration of fats and oils.

Possible measurement errors include insufficient reaction time for iodine addition, decomposition of iodine caused by light, deviations in titration endpoint determination, and errors in weighing the sample mass.
Particularly in reactions involving iodine, light protection and control of reaction time are important, and if the conditions are inconsistent, the iodine value may be underestimated.

Summary

Iodine value is an indicator representing the amount of double bonds contained in fats and oils.
The amount of iodine added to the fat or oil is determined from the difference between the blank titration volume and the sample titration volume and calculated as a value per 100 g of fat or oil.

In this reference example, iodine values were large in oils with high degrees of unsaturation, such as fish oil, soybean oil, and canola oil, and small in coconut oil.
In a report, it is useful to discuss iodine value, degree of unsaturation, decreases during storage, susceptibility to oxidation, and the relationship with peroxide value in relation to one another.

Relationship Between Unsaturated Bonds and Iodine Addition

Unsaturated fatty acids in fats and oils contain carbon-carbon double bonds.
These double bonds undergo addition reactions with halogens such as iodine and bromine.
Iodine-value measurement uses the amount of halogen that adds to these double bonds to evaluate the amount of unsaturated bonds.

The more double bonds a fat or oil contains, the more iodine can add.
Therefore, fats and oils with high iodine values are considered to contain larger amounts of unsaturated fatty acids, while fats and oils with low iodine values are considered to contain higher proportions of saturated fatty acids.
However, because fats and oils are mixtures containing multiple fatty acids, iodine value represents an average degree of unsaturation.

R-CH=CH-R’ + I2 → R-CHI-CHI-R’

Discussion of Fats and Oils With High Iodine Values

Fats and oils with high iodine values contain large amounts of unsaturated bonds.
In fats and oils containing large amounts of unsaturated fatty acids such as linoleic acid, linolenic acid, and oleic acid, many halogen molecules add to the double bonds, resulting in high iodine values.
Some vegetable oils and fish oils may have relatively high iodine values.

Fats and oils with high iodine values tend to be more susceptible to oxidation.
Double bonds readily react with oxygen, and oxidation may produce peroxides, aldehydes, and other compounds.
Therefore, although fats and oils with high iodine values have nutritional characteristics, attention must be paid to oxidative deterioration during storage.

Discussion of Fats and Oils With Low Iodine Values

Fats and oils with low iodine values are considered to contain fewer unsaturated bonds and relatively larger amounts of saturated fatty acids.
Saturated fatty acids do not contain carbon-carbon double bonds and therefore hardly undergo iodine-addition reactions.
As a result, the amount of halogen consumed is small and the iodine value is also low.

Fats and oils with low iodine values are generally less susceptible to oxidation and tend to have higher storage stability.
However, resistance to oxidation is affected not only by degree of unsaturation but also by antioxidant components, degree of refining, storage temperature, light, and contact with oxygen.
Iodine value provides a clue for considering oxidative stability but cannot be used alone to make a complete judgment.

Degree of Unsaturation and Susceptibility to Oxidation

The susceptibility of fats and oils to oxidation is related to the number of unsaturated bonds.
The double bonds of unsaturated fatty acids are susceptible to oxidation, and oxidation proceeds particularly readily in polyunsaturated fatty acids containing multiple double bonds.
As oxidation progresses, peroxides, aldehydes, ketones, and other compounds are generated, leading to deterioration of odor and taste.

Fats and oils with high iodine values have high degrees of unsaturation and tend to be more susceptible to oxidation.
However, oxidation may be suppressed when antioxidants are present in the fat or oil or when the fat or oil is stored under light-blocking, low-temperature, and sealed conditions.
Susceptibility to oxidation should be discussed not only in relation to iodine value but also in relation to storage conditions.

Relationship With Drying Oils, Semi-Drying Oils, and Non-Drying Oils

Fats and oils may be classified as drying oils, semi-drying oils, and non-drying oils according to how readily they dry in air.
Drying oils contain many unsaturated bonds and readily react with oxygen in the air to polymerize and harden.
In general, fats and oils with higher iodine values tend to show stronger drying properties.

Semi-drying oils contain a certain amount of unsaturated bonds but not as many as drying oils.
Non-drying oils have relatively low iodine values and do not readily harden in air.
However, the boundaries of these classifications are not strictly fixed and may vary depending on the composition of the fat or oil and measurement conditions.

Difference Between Iodine Value and Saponification Value

Iodine value is an indicator of the amount of unsaturated bonds in fats and oils.
In contrast, saponification value represents the amount of KOH required to saponify 1 g of fat or oil and is mainly related to fatty-acid chain length and the average molecular weight of the fat or oil.
In other words, iodine value and saponification value are both values describing properties of fats and oils, but they represent different things.

A fat or oil with a high iodine value is considered to have a high degree of unsaturation, but this does not necessarily mean that its fatty-acid chains are short.
Conversely, a fat or oil with a high saponification value may have a small average molecular weight, but this does not necessarily mean that it contains many unsaturated bonds.
In a report, the meanings of the two values must be distinguished and not confused.

Relationship With Acid Value and Peroxide Value

In fat and oil analysis, acid value and peroxide value are also commonly used in addition to iodine value.
Acid value indicates the amount of free fatty acids and serves as an indicator of hydrolytic deterioration of fats and oils.
Peroxide value is a value indicating the amount of peroxides produced during the early stages of oxidation of fats and oils.
Iodine value indicates the degree of unsaturation and does not directly represent deterioration itself.

However, fats and oils with high iodine values contain many unsaturated bonds and therefore tend to be more susceptible to oxidation.
Consequently, when considering oxidative deterioration, evaluating iodine value together with peroxide value makes the results easier to understand.
Iodine value can be regarded as an indicator of the structural background of susceptibility to oxidation, while peroxide value indicates the actual progress of oxidation.

Concept of the Wijs Method and Hanus Method

Methods for measuring iodine value include the Wijs method and Hanus method.
In these methods, a halogen is added to the unsaturated bonds in fats and oils, and the amount of unreacted halogen is determined by titration.
The amount of halogen consumed by the fat or oil is calculated from the difference from the blank test and expressed as the iodine value.

Although the reagents used differ depending on the experimental method, the basic concept is to determine the amount of halogen added to the unsaturated bonds.
If the reaction time, dark conditions, or amount of reagent is inappropriate, the addition reaction may be incomplete or side reactions may occur, resulting in errors in the iodine value.

Importance of the Blank Test

In iodine-value measurement, a blank test in which the same reagent procedures are performed without adding the fat or oil sample is necessary.
The blank test determines how much of the initially added halogen reagent is titrated.
In the sample test, halogen is consumed by addition to the unsaturated bonds in the fat or oil, so the amount of remaining halogen is smaller than in the blank test.

The difference between the blank-test and sample-test titration volumes corresponds to the amount of halogen that added to the fat or oil.
Without a blank test, the amount of halogen actually consumed by the fat or oil cannot be accurately determined.
The blank test also serves to correct for changes in reagent concentration and changes occurring during the procedure.

Concept of Sodium Thiosulfate Titration

In iodine-value measurement, unreacted iodine may be titrated with a sodium thiosulfate standard solution.
Iodine, I2, is reduced to iodide ions, I-, by thiosulfate ions, S2O32-.
This reaction is used to determine the amount of iodine remaining.

Near the endpoint of the titration, adding starch indicator causes a blue-violet color to appear because of the iodine-starch reaction.
When sodium thiosulfate is added and the iodine disappears, the blue-violet color disappears, and this point is taken as the endpoint.
Deviations in endpoint determination directly affect the iodine value.

I2 + 2S2O32- → 2I- + S4O62-

Starch Indicator and Endpoint Determination

Starch indicator reacts with iodine to produce a blue-violet color.
In sodium thiosulfate titration, the starch indicator is added after the amount of iodine has become small, and the point at which the blue-violet color disappears is taken as the endpoint.
If starch is added from the beginning, iodine may be strongly retained and the endpoint may become difficult to determine.

If too much sodium thiosulfate is added beyond the endpoint, the amount of remaining iodine cannot be correctly determined.
Near the endpoint, the titrant is added one drop at a time, the solution is thoroughly mixed, and the point at which the blue-violet color completely disappears is confirmed.
Turbidity caused by fats, oils, or solvents may make disappearance of the color difficult to judge.

Effect of Reaction Time

A certain reaction time is required for halogen addition to the unsaturated bonds in fats and oils.
If the reaction time is too short, addition to the unsaturated bonds may not proceed completely and the amount of iodine consumed by the fat or oil may be underestimated.
As a result, the iodine value is determined as too low.

On the other hand, if the reaction time is too long or the reaction is affected by light, side reactions or decomposition of the reagent may occur.
Therefore, it is important to follow the reaction time and dark conditions specified in the laboratory manual.
When comparing multiple samples, the reaction times must be kept consistent.

Effect of Light and Dark Conditions

Iodine and halogenating reagents may decompose or undergo side reactions when exposed to light.
In addition, oxidation of unsaturated fatty acids may also be promoted by light.
Therefore, iodine-value measurement may specify that the reaction be carried out in the dark.

If dark conditions are not maintained, changes other than the amount of halogen that actually reacted with the fat or oil may affect the titration value.
If the amount of light exposure differs among samples during the reaction, the reliability of comparisons also decreases.
It is important to shield the reaction containers from light and react all samples under the same conditions.

Effect of Sample Amount

Because iodine value is expressed as the amount of iodine added per 100 g of fat or oil, errors in weighing the sample affect the result.
If the sample mass is recorded as smaller than the actual value, the calculated iodine value becomes higher.
Conversely, if the sample mass is recorded as larger, the calculated iodine value becomes lower.

In addition, if too much fat or oil is used, the reaction reagent may become insufficient or the addition reaction may not proceed completely.
If too little is used, the difference in titration volume becomes small and the effect of reading errors becomes larger.
It is important to accurately weigh the sample amount specified in the laboratory manual.

Causes of Error in Iodine-Value Measurement

Causes of error in iodine-value measurement include errors in weighing the sample, insufficient reaction time, inadequate dark conditions, decomposition of the halogenating reagent, insufficient amount of reaction reagent, errors in endpoint determination, concentration errors in the sodium thiosulfate standard solution, variation in blank-test values, and insufficient dissolution of the fat or oil.
Because the iodine value is determined from the difference from the blank test, even small deviations in titration values have an effect.

Causes that make the value lower include incomplete addition reactions, short reaction times, and insufficient dissolution of the sample.
Causes that make the value higher include side reactions, deviations in endpoint determination, and underestimation of the sample mass.
Organizing the causes of error into overestimation and underestimation makes the discussion easier.

When the Results Can Be Considered Good

Iodine-value measurements can be considered to have produced good results when the blank-test and sample-test titration values are stable, variation among multiple iodine-value measurements is small, and the results do not contradict the trends expected from the types of fats and oils.
For example, obtaining high iodine values for fats and oils containing large amounts of unsaturated fatty acids and low iodine values for fats and oils containing large amounts of saturated fatty acids can be considered a reasonable trend.

In addition, if the reaction time and dark conditions are followed and the endpoint color can be clearly determined, the reliability of the results increases.
When comparing with literature values, differences caused by variety, place of origin, degree of refining, and storage condition of the fats and oils must also be considered.

Example Discussion When the Experiment Did Not Go Well

When iodine-value measurement does not go well, possible causes are considered from results such as variation in titration values, iodine values far from literature values, an excessively small difference from the blank test, difficulty determining the endpoint color, or a nonuniform reaction solution.
Organizing the causes according to sample amount, reaction time, dark conditions, reagent concentration, endpoint determination, and blank testing makes the discussion easier.

How to Write Points for Improvement

In a discussion of iodine-value measurement, writing not only the causes of error but also points for improvement makes the report easier to organize.
Points for improvement can be organized according to sample weighing, reaction operation, titration operation, standard solution, and calculation and analysis.

Improvements to Sample and Reaction Operations

• Accurately weigh the fat or oil sample
• Completely dissolve the fat or oil in the reaction solvent
• Add the reaction reagent accurately
• Follow the specified reaction time
• Maintain dark conditions during the reaction
• Keep the reaction conditions consistent for all samples
• Use the specified sample amount so that the reagent does not become insufficient

Improvements to Titration Operations

• Confirm the concentration of the sodium thiosulfate standard solution
• Perform the blank test under the same conditions
• Remove air bubbles from the burette
• Read the scale at eye level
• Add the starch indicator at the appropriate time
• Add the titrant one drop at a time near the endpoint
• Carefully confirm disappearance of the blue-violet color

Improvements to Calculation and Analysis

• Correctly use the difference between the blank-test and sample-test titration volumes
• Accurately reflect the sample mass
• Confirm the units of the iodine value
• Correctly convert the value to an amount per 100 g
• Perform multiple measurements and calculate the average value
• Compare with literature values and other fats and oils
• Distinguish the meanings of iodine value, saponification value, acid value, and peroxide value

Difference Between a Superficial Discussion and a Good Discussion

In a discussion of iodine-value measurement of fats and oils, simply writing that “the iodine value was high” or “the degree of unsaturation was high” results in a superficial discussion.
A good discussion relates the addition reaction to unsaturated bonds, susceptibility to oxidation, drying properties, blank testing, endpoint determination, and causes of error.

Examples of Expressions That Can Be Used in Reports

The following expressions can be used when writing the results and discussion of iodine-value measurements of fats and oils.
Adjust the necessary parts according to your own experimental results.

• The iodine value is the number of grams of iodine that add to 100 g of fat or oil.
• The iodine value is an indicator of the amount of unsaturated bonds in fats and oils.
• Halogens add to the double bonds of unsaturated fatty acids.
• Fats and oils with higher iodine values are considered to contain larger amounts of unsaturated fatty acids.
• Fats and oils with lower iodine values may contain higher proportions of saturated fatty acids.
• Fats and oils containing many unsaturated bonds are susceptible to oxidation and tend to deteriorate during storage.
• Fats and oils with high iodine values tend to show the properties of drying oils.
• Iodine value indicates the degree of unsaturation and has a different meaning from saponification value and acid value.
• The amount of iodine added to the fat or oil is determined from the difference between the blank-test and sample-test titration volumes.
• Insufficient reaction time and inadequate dark conditions are causes of error in iodine-value measurement.

Points to Check When Discussing the Iodine Value of Fats and Oils

Checking the following points before writing the report makes the discussion easier to write.

• Is the definition of iodine value explained?
• Is iodine addition to unsaturated bonds explained?
• Is the relationship between iodine value and degree of unsaturation described?
• Are the characteristics of fats and oils with high and low iodine values explained?
• Is the relationship with susceptibility to oxidation considered?
• Is the relationship with drying oils, semi-drying oils, and non-drying oils considered?
• Are the differences from saponification value, acid value, and peroxide value distinguished?
• Is the meaning of the blank test explained?
• Is the sodium thiosulfate titration reaction understood?
• Are the starch indicator and endpoint determination explained?
• Are the effects of reaction time and dark conditions considered?
• Do the points for improvement correspond to the causes of error?

Summary

The iodine value of fats and oils is the number of grams of iodine that add to 100 g of fat or oil and is an indicator of the amount of unsaturated bonds contained in fats and oils.
Because iodine and other halogens add to the carbon-carbon double bonds of unsaturated fatty acids, fats and oils containing more double bonds have higher iodine values.
Conversely, fats and oils containing large amounts of saturated fatty acids have lower iodine values.

Fats and oils with high iodine values have high degrees of unsaturation and tend to be susceptible to oxidation.
Unsaturated bonds readily react with oxygen, and during storage they may produce peroxides and decomposition products, leading to deterioration of odor and taste.
Iodine value also provides a clue for considering the properties of drying oils, semi-drying oils, and non-drying oils.

In a report, rather than simply writing that “the iodine value was high or low,” organize and discuss the addition reaction to unsaturated bonds, susceptibility to oxidation, drying properties, blank testing, sodium thiosulfate titration, starch indicator, reaction time, dark conditions, causes of error, and points for improvement.
Iodine value is an important analytical value for understanding the relationship between the structure and properties of fats and oils.