Frémy's salt

Frémy's salt
Names
	IUPAC name Potassium nitrosodisulfonate
Identifiers
CAS Number	14293-70-0 ;
3D model (JSmol)	Interactive image;
ChemSpider	2297553;
ECHA InfoCard	100.034.729
EC Number	238-219-0;
PubChem CID	3032624;
UNII	1989UAX6B9 ;
	InChI InChI=1S/2K.H2NO7S2/c;;2-1(9(3,4)5)10(6,7)8/h;;(H,3,4,5)(H,6,7,8)/q2*+1;/p-2 Key: IHSLHAZEJBXKMN-UHFFFAOYSA-L;
	SMILES N([O])(S(=O)(=O)[O-])S(=O)(=O)[O-].[K+].[K+];
Properties
Chemical formula	K2NO(SO3)2
Molar mass	268.33 g/mol (potassium salt)
Appearance	Yellowish-brown solid
Hazards
	GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H260, H302, H312, H332
Precautionary statements	P223, P231+P232, P280, P301+P312, P302+P352+P312, P304+P340+P312
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Frémy's salt is a chemical compound with the formula (K₄[ON(SO₃)₂]₂), sometimes written as (K₂[NO(SO₃)₂]). It is a bright yellowish-brown solid, but its aqueous solutions are bright violet. The related sodium salt, disodium nitrosodisulfonate (NDS, Na₂ON(SO₃)₂, CAS 29554-37-8) is also referred to as Frémy's salt.

Regardless of the cations, the salts are distinctive because aqueous solutions contain the radical [ON(SO₃)₂]²⁻.