Peroxydisulfuric Acid - H₂S₂O₈

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What is Peroxydisulfuric Acid?

Peroxydisulfuric Acid is described as a colourless solid and also one of the most powerful peroxy acid oxidants that are available currently. This Acid is an inorganic compound having the chemical formula H2S2O8. It can be generated either from ammonium persulfate or potassium in an acidic solution. It is given as an anhydride of peroxydisulfuric and sulphuric acid and can be prepared by the oxidation of oleum either with ozone or hydrogen peroxide. This is also known as Marshall's acid; peroxydisulfuric acid is produced by electrolyzing an aqueous solution that contains sulfate ions in an electrolysis reactor should be produced by process of electrolyzing.

Peroxydisulfuric Acid Structure H2S2O8

Let us look at the peroxydisulfuric acid structure H2S2O8, which can be illustrated as follows:

(Image to be added soon)

Let us look at some important properties of Peroxydisulfuric Acid below

Properties of Peroxydisulfuric Acid


Peroxydisulfuric Acid

Molecular Weight or Molar Mass

194.14 g/mol



Melting Point

65 °C

Conjugate base‎


Chemical Formula


Physical Properties of Peroxydisulfuric Acid H2S2O8


Colourless solid



Heavy Atom Count


Covalently-Bonded Unit



Soluble in water

Hydrogen Bond Acceptor


Chemical Properties of Peroxydisulfuric Acid H2S2O8

  • Peroxydisulfuric Acid dissolves in the water and forms sulphuric acid and hydrogen peroxide. The chemical equation for this can be given as follows:

H2S2O8 + 2H2O → H2O2 + 2H2SO4

  • Also, the Peroxydisulfuric Acid reacts with silver nitrate in the aqueous medium and produces silver oxide, nitric acid, and sulphuric acid. The chemical equation for this can be given as follows:

H2S2O8 + 2AgNO3 + 2H2O → Ag2O2 + 2H2SO4+ 2HNO3

Preparation of Peroxydisulfuric Acid

Peroxydisulfuric Acid can be prepared by adding the concentrated sulfuric acid to the sodium persulfate compound. Also, this acid can be prepared using chlorosulfuric acid, including a hydrogen peroxide reaction. The chemical equation for the same can be given as follows:

2CISO3H + H2O2 → H2S2O8 + 2HCl

The solid form is much difficult to obtain and is more often encountered as a solution.

Uses of Peroxydisulfuric Acid – H2S2O8

Let us look at the important uses of Peroxydisulfuric Acid, which are listed as follows:

  • The peroxydisulfuric acid usage and its salts as a hydrogen peroxide source opened the way for the production of large-scale sulphuric acid.

  • In photography, it can be used as a hypo eliminator.

  • It can also be used as a strong oxidant, whereas the oxidizing agent quantity usage can be varied based on the desired reaction rate.

Identification of Good Oxidizing Agents

As we all know, the oxidizing agent is that which oxidizes the other element in a chemical reaction, but itself gets reduced. For showing good oxidizing properties, it should contain a great tendency to gain electrons as we probably know the loss of electrons is defined as oxidation, and gain of electrons is defined as reduction as itself gets reduced. Therefore, it must gain electrons, where the oxidizing tendency of the oxidant depends upon its electronegativity, and the Ionisation potential and electron affinity should be high.

For suppose, potassium permanganate is considered as a good oxidizing agent, and in this reaction, we can prove using a chemical reaction, as given below:

MnO4-  + 8H+ + 5e → Mn+2 + 4H2O

Where oxidation of Mn in its reactant side is +7, whereas, on the product side, it is given as +2, it means Mn gains 5e, and also the oxidizing power of a system can be compared with their standard reduction potential. And, the greater the value of reduction potential, the stronger is oxidizing property. For suppose, acidified KMnO4 (at E°= 1.52 volt) is given as a stronger oxidizing agent compared to acidified K2Cr2O7 solution (at E°= 1.30 volt) containing lower reduction potential.

Some Good Oxidizing Agents

In the simplest form, an oxidizing agent is defined as something that adds oxygen to a compound and was the most accepted definition until recently.

However, understanding the concept of stoichiometry and the redox reaction, the oxidizing agent meaning has taken a new form.

The most precise definition of an oxidizing agent can be a chemical compound that either may or may not add an oxygen atom to the compound and change the formulae and chemical structure, but for sure, it increases the oxidation state of the other reagent present while reducing the state of oxidation of itself.

Acidified Potassium Dichromate (K2Cr2O7) is one of the most common examples of an oxidizing agent, which looks orange in colour. When H2S or SO2 gas is passed through it, Cr, which is present in the oxidation state of +6, reduces to an oxidation state of +3, which is green in colour and oxidizes from SO2 to SO4- ( + 4 to +6 ) or with S (-2 to 0 ) respectively. Considering the latter test, the turbidity presence indicates the formation of Sulphur (S), which is present in the colloid form.

FAQ (Frequently Asked Questions)

1. What is Peroxydisulfuric acid?

Peroxydisulfuric acid is defined as an inorganic compound having a chemical formula H2S2O8. It is also known as Marshall's acid, and after its inventor, Professor Hugh Marshall, it became a sulfur oxoacid. It can be written as HO3SOOSO3H in structural terms. It also contains sulfur in its +6 oxidation state, including a peroxide group. Its salts are commonly known as persulfates and are industrially essential as powerful oxidizing agents.

2. Explain what determines the strength of the reducing agents and oxidizing agents?

The strength of the oxidizing agents can be defined by their oxidation state, as in Cl+7, which cannot be further oxidized because of its valency. And Cl is in its maximum oxidation state. Hence, it can only be reduced; that is why it now behaves as a strong oxidizing agent. Whereas, Cl+5 behaves as a reducing agent and as an oxidizing agent as well.

3. Differentiate between Oxidizing Agents and Reducing Agents?

An oxidizing agent is defined as a substance that looks to remove electrons from the substance it is reacting with (it means oxidize it or increase its oxidation state). In contrast, a reducing agent looks to add the electrons to its reactant (it means, reduce it or reduce its oxidation state). In every case, the opposite takes place to the agent itself (an oxidizing agent can be reduced and gains either one or more electrons, where a reducing agent is oxidized and lose either one or more electrons).

4. Explain if the water is either an oxidizing agent or a reducing agent?

Since water is neither a strong oxidant agent nor a strong reducing agent, it can be either one among them depending on the substance that it is going to react with.