Hydrogenoxalate or hydrogen oxalate is an
anion
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...
with
chemical formula
In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, ...
or , derived from
oxalic acid
Oxalic acid is an organic acid with the systematic name ethanedioic acid and formula . It is the simplest dicarboxylic acid. It is a white crystalline solid that forms a colorless solution in water. Its name comes from the fact that early inve ...
by the loss of a single
proton
A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' elementary charge. Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton–electron mass ...
; or, alternatively, from the
oxalate
Oxalate (IUPAC: ethanedioate) is an anion with the formula C2O42−. This dianion is colorless. It occurs naturally, including in some foods. It forms a variety of salts, for example sodium oxalate (Na2C2O4), and several esters such as dimethyl o ...
anion by addition of a proton. The name is also used for any
salt
Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quantitie ...
containing this anion. Especially in older literature, hydrogenoxalates may also be referred to as bioxalates, acid oxalates, or monobasic oxalates. Hydrogenoxalate is
amphoteric
In chemistry, an amphoteric compound () is a molecule or ion that can react both as an acid and as a base. What exactly this can mean depends on which definitions of acids and bases are being used.
One type of amphoteric species are amphiproti ...
, in that it can react both as an acid or a base.
Well characterized salts include
sodium hydrogenoxalate
Sodium hydrogenoxalate is salt (ionic compound) of formula , consisting of sodium cations and hydrogenoxalate anions or . The anion can be described as the result of removing one hydrogen ion from oxalic acid , or adding one to the oxalate a ...
(),
potassium hydrogenoxalate
Potassium hydrogenoxalate is a salt with formula KHC2O4 or K+·HO2C-CO2−. It is one of the most common salts of the hydrogenoxalate anion, and can be obtained by reacting potassium hydroxide with oxalic acid in 1:1 mole ratio.
The salt is ...
(), ammonium hydrogenoxalate (), rubidium hydrogenoxalate () and dimethylammonium hydrogenoxalate (()).
Structure
Most hydrogenoxalate salts are
hydrated
Drinking is the act of ingesting water or other liquids into the body through the mouth, proboscis, or elsewhere. Humans drink by swallowing, completed by peristalsis in the esophagus. The physiological processes of drinking vary widely among o ...
. For example, potassium hydrogen oxalate crystallizes as 2·. These materials exhibit extended structures resulting from extensive hydrogen bonding and anion-cation interactions. The hydrates dehydrate upon heating:
:2· → 2 +