chemistry

Peroxide value

Peroxide value is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Peroxide value rather than just read about it. In short: Detection of peroxide gives the initial evidence of rancidity in unsaturated fats and oils. Other methods are available, but peroxide value is the most widely used.

Key takeaways

Peroxide value belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Peroxide value to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Peroxide value from memory before moving on to harder problems.

Reference excerpt

Detection of peroxide gives the initial evidence of rancidity in unsaturated fats and oils. Other methods are available, but peroxide value is the most widely used. It gives a measure of the extent to which an oil sample has undergone primary oxidation; extent of secondary oxidation may be determined from p-anisidine test. The double bonds found in fats and oils play a role in autoxidation. Oils with a high degree of unsaturation are most susceptible to autoxidation. The best test for autoxidation (oxidative rancidity) is determination of the peroxide value. Peroxides are intermediates in the autoxidation reaction. Autoxidation is a free radical reaction involving oxygen that leads to deterioration of fats and oils which form off-flavours and off-odours. Peroxide value, concentration of peroxide in an oil or fat, is useful for assessing the extent to which spoilage has advanced.

Definition The peroxide value is defined as the amount of peroxide oxygen per 1 kilogram of fat or oil. Traditionally this was expressed in units of milliequivalents, although in SI units the appropriate option would be in millimoles per kilogram (N.B. 1 milliequivalents = 0.5 millimole; because 1 mEq of O2 =1 mmol/2 of O2 =0.5 mmol of O2, where 2 is valence). The unit of milliequivalent has been commonly abbreviated as mequiv or even as meq.

Method The peroxide value is determined by measuring the amount of iodine which is formed by the reaction of peroxides (formed in fat or oil) with iodide ion.

2 I− + H2O + R−OOH → R−OH + 2 HO− + I2 The base produced in this reaction is taken up by the excess of acetic acid present. To measure the iodine, a redox titration is performed using sodium thiosulfate.

2 S2O2−3 + I2 → S4O2−6 + 2 I− The acidic conditions (excess acetic acid) prevents formation of hypoiodite (analogous to hypochlorite), which would interfere with the reaction. A starch indicator solution is used, for which amylose forms a blue to black solution with iodine and is colorless when the iodine is converted to iodide titrated.

Taste Peroxide values of fresh oils are less than 10 milliequivalents/kg; when the peroxide value is between 30* and 40 milliequivalents/kg, a rancid taste is noticeable.

See also Acid value Amine value Bromine number Epoxy value Hydroxyl value Iodine value Saponification value

References

Illustrations

Worked examples

Example 1 — a first encounter with Peroxide value

Start with the simplest possible case. Write down what Peroxide value claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Peroxide value before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Peroxide value ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Peroxide value

In research: Peroxide value appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Peroxide value in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Peroxide value is common in secondary-school and first-year university syllabi. It links to neighbouring topics Edible oil chemistry, Flavors, Food analysis, so understanding it makes those chapters shorter.
In everyday life: Look for Peroxide value outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Peroxide value in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Peroxide value means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Peroxide value out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Peroxide value in simple terms?

Detection of peroxide gives the initial evidence of rancidity in unsaturated fats and oils. Other methods are available, but peroxide value is the most widely used.

Why does Peroxide value matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Peroxide value?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Peroxide value.