The difference between sodium dihydrogen phosphate and disodium hydrogen phosphate

 H2PO4- is ionization greater than hydrolysis, HPO42- is more hydrolyzed than ionization, so acid-base is different, ionization is greater than hydrolysis or hydrolysis is greater than ionization, depending on the ionization constant.

Phosphoric acid is a weak acid and its acid radicals hydrolyze in water.

Among them HPO42- will react as follows:
HPO42-+H2O=H3PO4+OH-, hydrolysis
HPO42-=H++PO43-, ionization
Both of these are reversible reactions, but the degree of hydrolysis is greater than the degree of ionization, resulting in OH->H+, so it is alkaline.
H2PO4-+H2O=H3PO4+OH-
H2PO4-=HPO4-+H+
The ionization is greater than hydrolysis, and H+>OH- is so acidic.
sodium dihydrogen phosphate is used in boiler water treatment, acidity buffer, detergent, baking powder, mica sheeting, dye additives, tanning, electroplating, etc. It is also a raw material for the production of sodium dihydrogen phosphate, sodium acid pyrophosphate and sodium hexametaphosphate. Used as a buffer, emulsifier, nutrient, etc. in foods and beverages.

disodium hydrogen phosphate buffer solution, preparation chemistry, use of weak alkali, phosphating solution, fire fighting equipment, etc. Used as industrial water treatment agent, printing and dyeing detergent, quality improver, antibiotic culture agent, biochemical treatment agent, etc. Used as flame retardant for fabrics, wood and paper, and weighting agent for silk. It is an auxiliary agent for producing reactive dyes. Used instead of borax in welding and brazing as a food quality improver.