What is oxalic acid?
Oxalic acid is a dicarboxylic acid wherein both carboxy groups are directly bonded to each other. The pure water-free substance occurs as a white crystalline powder, which is sparingly soluble in water. Oxalic acid forms by crystallization in aqueous solutions with two molecules of water of crystallization is a dihydrate, which is colorless.
Averting
Oxalic acid and its derivatives occur in different plants, especially rhubarb and sorrel. Food products that contain substantial amounts of oxalic acid are cocoa, chocolate, most nuts, berries, beans and beets. It also happens in parsley and spinach.
Synthesis
Oxalic acid can be prepared by the acidification of sodium oxalate, which in turn can be prepared by heating sodium Formate at 360 ° c:
The annual amount of oxalic acid produced is 140,000 tons.
Structure and properties
The salts and esters of oxalic acid are called oxalates. The salts can be simply formed by reaction with a base. With sodium hydroxide, sodium oxalate is formed:
Esters can be prepared by esterification of an alcohol with oxalic acid.
Oxalic acid is one of the strongest carboxylic acids, with a first acid constant of 1.27. This is caused by the electron-withdrawing effect which the second carboxygroep. The first ionisatiestap is still more strongly promoted by intramolecular waterstofbrug formation. The second proton is more difficult, because there are already ceded a neighbouring negative charge is present (in the eerstgevormde carboxylaatgroep). So is the second acid constant larger (4,27).
In a potentiometric titration are the two ionisaties steps with difficulty to see separately. At a conductometric titration is the difference be fine to see, because the first step is behaving as a reasonably strong acid and weak acid the second step behaviour.
Applications
Household
Oxalic acid can also be found in household products and anti-rust agents. A solution of 1: 10 is used to remove out of wood and the weather is for sale under the name ' ontweringswater '.
Analytical chemistry
In analytical chemistry is oxalic acid (if dihydrate) as oertiterstof used for basic solutions such as sodium hydroxide and potassium hydroxide, but also solutions of oxidants such as potassium permanganate, kaliumperjodaat or potassium dichromate. Usually does one out of about 0,1 mol/L as standard concentration.
Clinical chemistry
In clinical chemistry is oxalic acid applied to the clot of blood. In blood clotting calcium-ion plays a key role. By the calcium oxalate to bind with it is no longer available for the clotting reaction and blood remains liquid.
Combating parasites on bees
Oxalic acid is a means to combat the Varroa mite (Varroa destructor). This mite is just about the biggest cause of the loss of European bees in the wild. Beekeepers these mites in their closets very well treated with a mixture of oxalic acid, water and sugar. This is either the bees or evaporates sprinkled down in the hive. The following day can be found on the control board lots of dead mites under the cabinet. Working with oxalic acid can only in certain periods. Winter is an ideal time since there is no brood and mites on the bees alive. If the mites once the brood has oxalic acid effects.
Toxicology and safety
When oxalic acid is ingested irritates the throat from the inside. Oxalic acid binds in the body with metal ions, such as calcium, which constitutes the oxalates that can irritate the throat and kidneys. Some kidney stones consist largely of oxalates.
Prolonged or repeated exposure to oxalic acid can damage the kidneys. On the eyes, a small amount of dust irritation (characterized by red and watery eyes) cause prolonged contact may cause corneal damage or even blindness. Repeated exposure to the skin gives tissue damage, inflammation or blisters, depending on the duration of exposure.
Inhalation of oxalic can have different degrees of lung damage, and cause irritation to the respiratory tract, characterized by burning sensation in the throat, coughing and cough. Large amounts may cause asphyxiation, unconsciousness and even death.