Disodium hydrogen phosphite is the name for inorganic compounds with the formula Na₂HPO₃ₓ. The commonly encountered salt is the pentahydrate. A derivative of phosphorous acid, it contains the anion HPO₃²⁻. Its common name suggests that it contains an acidic hydrogen atom, as in sodium hydrogen carbonate.

What is Na3PO3?

Trisodium phosphite | Na3PO3 - PubChem.

What is sodium phosphite used for?

Sodium phosphate is used in adults 18 years of age or older to empty the colon (large intestine, bowel) before a colonoscopy (examination of the inside of the colon to check for colon cancer and other abnormalities) so that the doctor will have a clear view of the walls of the colon.