Tutton's salts are a family of
salts
In chemistry, a salt or ionic compound is a chemical compound consisting of an assembly of positively charged ions ( cations) and negatively charged ions (anions), which results in a compound with no net electric charge (electrically neutral). ...
with the
formula
In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwe ...
M
2M'(SO
4)
2(H
2O)
6 (sulfates) or M
2M'(SeO
4)
2(H
2O)
6 (selenates). These materials are
double salts
A double salt is a salt that contains two or more different cations or anions. Examples of double salts include alums (with the general formula ) and Tutton's salts (with the general formula ). Other examples include potassium sodium tartrate, a ...
, which means that they contain two different cations, M
+ and M'
2+ crystallized in the same regular ionic lattice.
The univalent cation can be
potassium
Potassium is a chemical element; it has Symbol (chemistry), symbol K (from Neo-Latin ) and atomic number19. It is a silvery white metal that is soft enough to easily cut with a knife. Potassium metal reacts rapidly with atmospheric oxygen to ...
,
rubidium
Rubidium is a chemical element; it has Symbol (chemistry), symbol Rb and atomic number 37. It is a very soft, whitish-grey solid in the alkali metal group, similar to potassium and caesium. Rubidium is the first alkali metal in the group to have ...
,
caesium
Caesium (IUPAC spelling; also spelled cesium in American English) is a chemical element; it has Symbol (chemistry), symbol Cs and atomic number 55. It is a soft, silvery-golden alkali metal with a melting point of , which makes it one of only f ...
,
ammonium
Ammonium is a modified form of ammonia that has an extra hydrogen atom. It is a positively charged (cationic) polyatomic ion, molecular ion with the chemical formula or . It is formed by the protonation, addition of a proton (a hydrogen nucleu ...
(NH
4), deuterated ammonium (ND
4) or
thallium
Thallium is a chemical element; it has Symbol (chemistry), symbol Tl and atomic number 81. It is a silvery-white post-transition metal that is not found free in nature. When isolated, thallium resembles tin, but discolors when exposed to air. Che ...
.
Sodium
Sodium is a chemical element; it has Symbol (chemistry), symbol Na (from Neo-Latin ) and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 element, group 1 of the peri ...
or
lithium
Lithium (from , , ) is a chemical element; it has chemical symbol, symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard temperature and pressure, standard conditions, it is the least dense metal and the ...
ions are too small. The divalent cation can be
magnesium
Magnesium is a chemical element; it has Symbol (chemistry), symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 ...
,
vanadium
Vanadium is a chemical element; it has Symbol (chemistry), symbol V and atomic number 23. It is a hard, silvery-grey, malleable transition metal. The elemental metal is rarely found in nature, but once isolated artificially, the formation of an ...
,
chromium
Chromium is a chemical element; it has Symbol (chemistry), symbol Cr and atomic number 24. It is the first element in Group 6 element, group 6. It is a steely-grey, Luster (mineralogy), lustrous, hard, and brittle transition metal.
Chromium ...
,
manganese
Manganese is a chemical element; it has Symbol (chemistry), symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese was first isolated in the 1770s. It is a transition m ...
,
iron
Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...
,
cobalt
Cobalt is a chemical element; it has Symbol (chemistry), symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. ...
,
nickel
Nickel is a chemical element; it has symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive, but large pieces are slo ...
,
copper
Copper is a chemical element; it has symbol Cu (from Latin ) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orang ...
,
zinc
Zinc is a chemical element; it has symbol Zn and atomic number 30. It is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodic tabl ...
or
cadmium
Cadmium is a chemical element; it has chemical symbol, symbol Cd and atomic number 48. This soft, silvery-white metal is chemically similar to the two other stable metals in group 12 element, group 12, zinc and mercury (element), mercury. Like z ...
. In addition to sulfate and selenate, the divalent anion can be
chromate Chromate or chromat, and their derived terms, may refer to:
Chemistry
* Chromate and dichromate, ions
* Monochromate, an ion
* Trichromate, an ion
* Tetrachromate, an ion
* Chromate conversion coating, a method for passivating metals
Biolog ...
(CrO
42−),
tetrafluoroberyllate
Tetrafluoroberyllate or orthofluoroberyllate is an anion with the chemical formula . It contains beryllium and fluorine. This fluoroanion has a tetrahedral shape, with the four fluorine atoms surrounding a central beryllium atom. It has the same ...
(BeF
42−),
hydrogenphosphate
Phosphates are the naturally occurring form of the element phosphorus.
In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphor ...
(HPO
42−) or
monofluorophosphate
Monofluorophosphate is an anion with the formula , which is a phosphate group with one oxygen atom substituted with a fluoride atom. The charge of the ion is −2. The ion resembles sulfate in size, shape and charge, and can thus form compounds wi ...
(PO
3F
2−). Tutton's salts crystallize in the
monoclinic
In crystallography, the monoclinic crystal system is one of the seven crystal systems. A crystal system is described by three Vector (geometric), vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in t ...
space group
In mathematics, physics and chemistry, a space group is the symmetry group of a repeating pattern in space, usually in three dimensions. The elements of a space group (its symmetry operations) are the rigid transformations of the pattern that ...
''P''2
1/''a''. The robustness is the result of the complementary hydrogen-bonding between the tetrahedral anions and cations as well their interactions with the metal aquo complex
(H2O)6sup>2+.
Examples and related compounds
Perhaps the best-known is
Mohr's salt, ferrous ammonium sulfate (NH
4)
2Fe(SO
4)
2.(H
2O)
6). Other examples include the vanadous Tutton salt (NH
4)
2V(SO
4)
2(H
2O)
6 and the chromous Tutton salt (NH
4)
2Cr(SO
4)
2(H
2O)
6. In solids and solutions, the M'
2+ ion exists as a
metal aquo complex
In chemistry, metal aquo complexes are coordination compounds containing metal ions with only water as a ligand. These complexes are the predominant species in aqueous solutions of many metal salts, such as metal nitrates, sulfates, and perchlo ...
'(H2O)6sup>2+.
Related to the Tutton's salts are the
alum
An alum () is a type of chemical compound, usually a hydrated double salt, double sulfate salt (chemistry), salt of aluminium with the general chemical formula, formula , such that is a valence (chemistry), monovalent cation such as potassium ...
s, which are also double salts but with the formula MM'(SO
4)
2(H
2O)
12. The Tutton's salts were once termed "false alums".
File:MohriteD.jpg, Unit cell of ferrous ammonium sulfate (N is violet, O is red, S is orange, Fe is large red).
File:Mohrite-DwH-bonds.jpg, The same structure with hydrogen bond
In chemistry, a hydrogen bond (H-bond) is a specific type of molecular interaction that exhibits partial covalent character and cannot be described as a purely electrostatic force. It occurs when a hydrogen (H) atom, Covalent bond, covalently b ...
ing network highlighted.
History
Tutton salts are sometimes called Schönites after the naturally occurring mineral called
Schönite (K
2Mg(SO
4)
2(H
2O)
6). They are named for
Alfred Edwin Howard Tutton, who identified and characterised a large range of these salts around 1900.
Such salts were of historical importance because they were obtainable in high purity and served as reliable reagents and spectroscopic standards.
Table of salts
Organic salts
Some organic bases can also form salts that crystallise like Tutton's salts.
References
{{Reflist, 30em
*
Sulfates