Ammonium persulfate ((NH4)2S2O8) is a white powder. It dissolves in water and releases oxygen. It can bleach, etch, or initiate polymerization.
| IUPAC name | Ammonium peroxydisulfate |
| Molecular formula | (NH4)2S2O8 |
| CAS number | 7727-54-0 |
| Synonyms | Ammonium persulfate, Ammonium peroxodisulfate, Diammonium persulfate, Diammonium peroxydisulfate |
| InChI | InChI=1S/2H3N.H2O8S2/c;;1-9(2,3)7-8-10(4,5)6/h2*1H3;(H,1,2,3)(H,4,5,6) |
Ammonium Persulfate Properties
Ammonium Persulfate Formula
The formula of ammonium persulfate is (NH4)2S2O8. It consists of two ammonium cations (NH4+) and one persulfate anion (S2O82-). The persulfate anion has two sulfate groups (SO42-) connected by a peroxide bond (O-O).
Ammonium Persulfate Molar Mass
The molar mass of (NH4)2S2O8 is 228.18 g/mol. This is calculated by adding the atomic masses of all the atoms in the formula: 2 x 14.01 (N) + 8 x 1.01 (H) + 2 x 32.06 (S) + 8 x 16.00 (O).
Ammonium Persulfate Boiling Point
(NH4)2S2O8 does not have a boiling point because it decomposes before reaching that temperature. It decomposes at about 120 °C (248 °F) into ammonia, nitrogen, oxygen, and water. The decomposition reaction is:
(NH4)2S2O8 -> 2 NH3 + N2 + O2 + 2 H2O
Ammonium Persulfate Melting Point
(NH4)2S2O8 does not have a melting point because it decomposes before reaching that temperature. It decomposes at about 120 °C (248 °F) into ammonia, nitrogen, oxygen, and water. The decomposition reaction is:
(NH4)2S2O8 -> 2 NH3 + N2 + O2 + 2 H2O
Ammonium Persulfate Density g/mL
The density of (NH4)2S2O8 is 1.98 g/mL at 25 °C. This means that one milliliter of (NH4)2S2O8 weighs 1.98 grams.
Ammonium Persulfate Molecular Weight
The molecular weight of (NH4)2S2O8 is the same as its molar mass, which is 228.18 g/mol. This means that one mole of (NH4)2S2O8 weighs 228.18 grams.
Ammonium Persulfate Structure
The structure of (NH4)2S2O8 can be represented by the following Lewis structure:
O O
|| ||
O=S||-O-O-S||=O
|| ||
O O
/ \
H-N N-H
\ /
H
/ \
H-N N-H
\ /
H
In this structure, each sulfur atom is bonded to four oxygen atoms in a tetrahedral geometry, and each oxygen atom has two lone pairs of electrons. The peroxide bond between the two sulfate groups is a single bond with one electron pair. The ammonium cations are formed by nitrogen atoms sharing three electrons with three hydrogen atoms each, and having a positive charge.
Ammonium Persulfate Solubility
(NH4)2S2O8 is highly soluble in water, much more so than the related potassium salt1. It dissolves in water to form ammonium ions and persulfate ions, which can dissociate further into sulfate radicals:
(NH4)2S2O8 -> 2 NH4+ + S2O82-
S2O82- -> 2 SO4•-
The solubility of (NH4)2S2O8 in water increases with increasing temperature. At 25 °C, it can dissolve up to 80 g/100 mL of water. It is also moderately soluble in methanol.
| Appearance | White to yellowish crystals |
| Specific gravity | 1.98 |
| Color | White to yellowish |
| Odor | Mild and unpleasant |
| Molar mass | 228.18 g/mol |
| Density | 1.98 g/mL at 25 °C |
| Melting point | 120 °C (decomposes) |
| Boiling point | N/A (decomposes) |
| Flash point | N/A |
| Water solubility | 80 g/100 mL at 25 °C |
| Solubility | Moderately soluble in MeOH |
| Vapour pressure | N/A |
| Vapour density | N/A |
| pKa | N/A |
| pH | N/A |
Ammonium Persulfate Safety and Hazards
(NH4)2S2O8 is a strong oxidizing agent that can intensify fire and react explosively with combustible materials. It can also cause various health effects if swallowed, inhaled, or contacted with skin or eyes. It can irritate the skin, eyes, nose, throat, and lungs. It can also cause allergic reactions such as skin rash, asthma, or breathing difficulties. It is harmful to aquatic life. Therefore, it should be handled with care and proper protective equipment. It should be stored away from heat, sparks, flames, and other incompatible substances.
| Hazard symbols | O (Oxidizing), Xn (Harmful), Xi (Irritant) |
| Safety description | S17 (Keep away from combustible material), S26 (In case of contact with eyes, rinse immediately with plenty of water and seek medical advice), S36/37/39 (Wear suitable protective clothing, gloves and eye/face protection), S45 (In case of accident or if you feel unwell, seek medical advice immediately) |
| UN IDs | UN 1444 |
| HS code | 28334000 |
| Hazard class | 5.1 (Oxidizing substances) |
| Packing group | III |
| Toxicity | LD50 oral rat: 689 mg/kg, LC50 inhalation rat: 2.95 mg/L/4h, LD50 dermal rat: 2000 mg/kg |
Ammonium Persulfate Synthesis Methods
Various methods can be used to prepare (NH4)2S2O8, which is an inorganic salt.
One of the most common methods involves electrolyzing a cold, concentrated solution of ammonium sulfate ((NH4)2SO4) and sulfuric acid (H2SO4).
This method was first described by Hugh Marshall. The electrolysis involves passing an electric current through the solution using a platinum anode and a porous silver cathode.
At the anode, the electrolysis of sulfuric acid produces hydrogen sulfate ions HSO4-, which combine with water to create persulfate ions S2O82- and hydrogen gas H2. At the cathode, oxygen gas O2 undergoes reduction to yield hydrogen peroxide H2O2, which reacts with ammonium ions NH4+ to form (NH4)2S2O8 (NH4)2S2O8 and water H2O.
The overall reaction is:
(NH4)2SO4 + 2 H2SO4 -> (NH4)2S2O8 + 2 H2O + H2 + O2
By cooling and filtering, one can crystallize (NH4)2S2O8 from the electrolytic solution.
Another method for preparing (NH4)2S2O8 is the oxidation of ammonium bisulfate NH4HSO4 with ozone O3 or hydrogen peroxide H2O2. This method produces a higher yield and purity of (NH4)2S2O8 than the electrolysis method. The reaction is:
NH4HSO4 + O3 -> (NH4)2S2O8 + H2O
or
NH4HSO4 + H2O2 -> (NH4)2S2O8 + 2 H2O
Ammonium Persulfate Uses
(NH4)2S2O8 is a versatile chemical that has many uses in various industries and applications. Some of the most common uses are:
- It serves as a bleaching agent and a chemical precursor in the synthesis of other industrially important compounds.
- It initiates the polymerization process and manufacturers predominantly use it in the production of polystyrene.
- PCB manufacturers use it as an etchant to eliminate copper and other metals from the surface.
- The semiconductor sector also uses (NH4)2S2O8 as an etchant to clean and polish silicon wafers.
- Laboratories use it as a cleaning and disinfecting agent for equipment, glassware, and water systems.
- It prevents the browning of fruits and vegetables, making it an additive used to preserve food.
- Various chemical reactions use it as an oxidizing agent for the synthesis of organic peroxides, sulfones, and sulfonamides.
- Batteries use it as a depolarizer to increase their performance and lifespan.
- Hair bleaches use it as a common ingredient to lighten the hair color by oxidizing the melanin pigment.
Questions:
Q: How long does ammonium persulfate last?
A: (NH4)2S2O8 is a stable compound that can be stored indefinitely in solid state without decomposition. However, it can lose its potency over time when dissolved in water. The shelf life of a 10% (NH4)2S2O8 solution is about 2-4 weeks at room temperature and 2-3 months at 4 °C12. The solution should be protected from light and heat, and checked periodically for the presence of bubbles or precipitates, which indicate decomposition.
Q: What does ammonium persulfate do?
A: (NH4)2S2O8 is a strong oxidizing agent that can release oxygen radicals in aqueous solution. These radicals can initiate or accelerate various chemical reactions, such as polymerization, bleaching, etching, cleaning, and disinfecting. (NH4)2S2O8 can also act as a source of sulfate ions for the synthesis of other compounds.
Q: What to mix ammonium persulfate in?
A: (NH4)2S2O8 is highly soluble in water, and can be mixed with water to prepare solutions of different concentrations. The solubility of (NH4)2S2O8 in water increases with increasing temperature. At 25 °C, it can dissolve up to 80 g/100 mL of water. It is also moderately soluble in methanol. (NH4)2S2O8 should not be mixed with incompatible substances, such as combustible materials, reducing agents, metals, acids, or bases, as it can react violently or explosively with them.
Q: Is ammonium peroxidisulphate the same as ammonium persulfate?
A: Yes, ammonium peroxidisulphate is another name for (NH4)2S2O8. They are both synonyms for the same compound with the formula (NH4)2S2O8.
Q: What is ammonium persulfate used for in SDS-PAGE?
A: SDS-PAGE (sodium dodecyl sulfate-polyacrylamide gel electrophoresis) is a technique for separating proteins based on their size and charge. (NH4)2S2O8 is used as a catalyst for the polymerization of acrylamide and bisacrylamide monomers to form a polyacrylamide gel matrix. (NH4)2S2O8 generates free radicals that initiate the cross-linking reaction between the monomers.
Q: How to make 10% ammonium persulfate?
A: To make a 10% (NH4)2S2O8 solution, weigh 10 g of solid (NH4)2S2O8 and dissolve it in 90 mL of distilled water. Stir until completely dissolved and transfer to a 100 mL volumetric flask. Fill up to the mark with distilled water and mix well. Store the solution in a dark bottle at 4 °C or room temperature.
Q: How to repair an arc strike ammonium persulfate?
A: An arc strike is a defect caused by an electric arc that damages the surface of a metal. It can reduce the strength and corrosion resistance of the metal and lead to cracking or failure. To repair an arc strike, one method is to use (NH4)2S2O8 as an etchant to remove the affected area. The procedure is as follows:
- Clean the surface of the metal with acetone or alcohol to remove any dirt or grease.
- Apply a thin layer of ammonium persulfate solution (10-20%) to the arc strike area using a brush or cotton swab.
- Wait for 5-10 minutes until bubbles appear on the surface, indicating that the oxidation reaction is taking place.
- Rinse the surface with water and dry with a clean cloth.
- Repeat the process until the arc strike is completely removed.
- Inspect the surface for any cracks or pits and fill them with an appropriate filler material if needed.
- Apply a protective coating or paint to prevent further corrosion.
Q: Is ammonium persulfate a surfactant?
A: No, (NH4)2S2O8 is not a surfactant. A surfactant is a substance that reduces the surface tension of a liquid or between two liquids, and can form micelles or emulsions. (NH4)2S2O8 does not have these properties. It is an oxidizing agent that can release oxygen radicals in aqueous solution.
Q: What aspects of your experiment are controlled by TEMED and ammonium persulfate?
A: TEMED and (NH4)2S2O8 are used to control the polymerization of acrylamide and bisacrylamide monomers to form a polyacrylamide gel matrix for electrophoresis. TEMED and (NH4)2S2O8 act as catalysts that generate free radicals that initiate and accelerate the cross-linking reaction between the monomers. The concentration and ratio of TEMED and (NH4)2S2O8 affect the speed and completeness of the polymerization, as well as the pore size and mechanical strength of the gel.
Q: Does ammonium persulfate react with air?
A: Yes, (NH4)2S2O8 can react with air, especially in humid conditions. (NH4)2S2O8 can absorb moisture from the air and undergo hydrolysis, forming ammonium sulfate and hydrogen peroxide. Hydrogen peroxide can further decompose into water and oxygen gas, releasing heat and pressure. This can cause the container of (NH4)2S2O8 to rupture or explode if not properly vented. (NH4)2S2O8 can also react with oxygen in the air and form ozone, which is a toxic gas. Therefore, (NH4)2S2O8 should be stored in a cool, dry, and well-ventilated place, away from heat, sparks, flames, and other incompatible substances.