Oxalic acid is an organic compound with the formula C2H2O4. It is a colorless crystalline solid that forms a colorless solution in water. Its acid strength is much greater than that of acetic acid. Oxalic acid is a reducing agent and its conjugate base, known as oxalate, is a chelating agent for metal cations.
Oxalic acid is an odorless white solid. Sinks and mixes with water. It is a strong dicarboxylic acid occurring in many plants and vegetables. It is produced in the body by metabolism of glyoxylic acid or ascorbic acid. It is not metabolized but excreted in the urine. It is used as an analytical reagent and general reducing agent.
It occurs naturally in many foods, but excessive ingestion of oxalic acid or prolonged skin contact can be dangerous. Its name comes from the fact that early investigators isolated oxalic acid from wood-sorrel (Oxalis) flowering plants.
Leafy greens and other plant foods are very popular among the health conscious. However, many of these foods also contain an antinutrient called oxalate (oxalic acid). Foods high in oxalate include beet greens, rhubarb, spinach, beets, swiss chard, endive, cocoa powder and kale. Oxalic acid is the main acid present in tomatoes. As a tomato ripens, the amount of Vitamin C decreases and the amount of oxalic acid increases.
Oxalic acid is used for extractive metallurgy. It is an important reagent in lanthanide chemistry. Hydrated lanthanide oxalates form readily in very strongly acidic solutions in a densely crystalline, easily filtered form, largely free of contamination by non-lanthanide elements. Thermal decomposition of these oxalate gives the oxides, which is the most commonly marketed form of these elements. Oxalic acid is used by some beekeepers as a miticide against the parasitic varroa mite. Oxalic acid is used to clean minerals. Oxalic acid is sometimes used in the aluminum anodizing process, with or without sulfuric acid. Compared to sulfuric acid anodizing, the coatings obtained are thinner and exhibit lower surface roughness.
Oxalic Acid Uses and Applications in the United States
For Protecting Bees From Mites
pH Adjuster And Chelating Agent For Cosmetic Products
Textile Industry Processes
For Removing Stain From Wood Decks
For Cleaning Decks
For Cleaning Wood & Rocks
For Rust Removal
Oxalic acid can be purchased from Lab Alley, but it can also be prepared in a laboratory by oxidizing sucrose using nitric acid in the presence of a small amount of vanadium pentoxide as a catalyst.
About 25% of produced oxalic acid will be used as a mordant in dyeing processes. It is used in bleaches, especially for pulpwood. It is also used in baking powder and as a third reagent in silica analysis instruments. Oxalic acid's main applications include cleaning or bleaching, especially for the removal of rust (iron complexing agent). Its utility in rust removal agents is due to it forming a stable, water-soluble salt with ferric iron, ferrioxalate ion.
Aside from bleaching, rust removing, and stain removing, oxalic acid is also used as a reducing agent in developing photographic film. You can also find it used in wastewater treatment as well since oxalic acid can effectively remove calcium from wastewater. And lastly, oxalic acid is also used as a grinding agent when polishing marble.
Oxalic acid is commonly used by some beekeepers as a miticide against varroa mite. Oxalic acid has been approved by the EPA to treat honeybee colonies in the U.S. Oxalic acid cannot penetrate capped brood, so it is best to treat a hive when it has little to no sealed brood. It is the acid of choice when fighting varroa mites because it is organic, and it is a stronger acid than acetic or formic acid.
Oxalic Acid Used in Bleaching
Oxalic acid is used as a bleaching agent for both wood and stone. When wood is exposed to the elements it can turn grey. But when oxalic acid is applied to an old and graying wood floor, for example, it brings the wood back to a natural white color. It is also used when preparing to stain old wood floors. Oxalic acid can be used to lighten heavily stained areas of wood furniture when refinishing them.
Oxalic Acid Used in Removing Stains
Oxalic acid can remove ink, food, and many other types of stains. It is a gentle stain remover that eats the stain but leaves the base surfaces intact. It can be used to remove most stains found on various surfaces like stone, brick, linoleum, wood, and vinyl.
Oxalic Acid Used in Removing Rusts
Oxalic acid removes rusts that are found on plumbing pipes and kitchen countertops. It is a major ingredient found on commercial rust removers for sinks, tubs, and metal rust stains.
Oxalic acid is used as a reducing agent for photography and ink removal. It helps to dissolve the oxalates. It is used in the toning solution and for platinum printing.
Oxalic Acid Structure
Oxalic acid is a toxic acid, it is also called ethanedioic acid. It is a strong dicarboxylic acid. The chemical formula is (COOH)2 and its molecular formula is C2H2O4. Its molar mass is 90.03 g/mol.
Anhydrous oxalic acid exists as two polymorphs; one results in a chain-like structure. In the other form the hydrogen bonding structure forms a sheet-like structure. The material is both acidic and hydrophilic.
Oxalic Acid Safety, Hazards, and Storage
Oxalic acid in its concentrated form is poisonous and can have harmful effects through contact and ingestion. The toxicity of oxalic acid is due to kidney failure caused by precipitation of solid calcium oxalate, it can also cause joint pain.
As dust or as a solution, Oxalic Acid can cause severe burns of eyes, skin, or mucous membranes. Ingestion of 5 grams has caused death with symptoms of nausea, shock, collapse, and convulsions coming on rapidly. Repeated or prolonged skin exposure can cause dermatitis and slow-healing ulcers.
When storing oxalic acid keep it in a tightly closed, airtight container to prevent the absorption of moisture. If moisture gets into the container it will cause the loose crystalline powder to solidify into a hard rock. Store oxalic acid in a cool, dry, well-ventilated area away from heat.
When handling oxalic acid, wash thoroughly when finished to minimize dust generation and accumulation.
Ace Hardware sells a wood bleaching product that contains oxalic acid. Wood bleach works well to remove black water spots and tannin stains in wood. The oxalic acid in the wood bleach effectively bleaches unfinished wood quickly and easily.
Trisodium phosphate (TSP) is available at most hardware stores, it is used to remove surface soil and sticky substances. This product will clean your deck if it is mixed with bleach and scrubbed into the wood. After this process the wood might be darkened or discolored due to weathering. In order to remove these stains oxalic acid is used. TSP is used to clean the wood and oxalic acid is used to remove stains or discoloration. They are not the same product.
Oxalic acid is commonly used as a wood bleach because it removes stains without removing the natural look of the wood. When using it first clean the wood completely then apply the acid until the stain is removed.