Baking soda is the common name of sodium thiosulfate, also called Hypo (transliteration of hypo), with five crystal waters (Na2S2O3·5H2O), so it is also called sodium thiosulfate pentahydrate.

Sodium bicarbonate is a colorless and transparent crystal, easily soluble in water, and its aqueous solution is weakly alkaline. It is weathered in dry air above 33℃ and loses crystal water. It is stable in neutral and alkaline solutions and will decompose rapidly in acidic solutions.

Na2S2O3+2HCl====2NaCl+H2O+S↓+SO2↑?

Soda has a strong complexing ability and can form a complex with silver bromide. The reaction formula: agbr+2na2s2o3 = = = nabr+na3 [ag (s2o3) 2]. According to this property, it can be used as a fixing agent. During phase washing, excessive baking soda reacts with the silver bromide of the unexposed part of the negative film, and is converted into soluble Na2 [Ag (S2O3) 2], and the AgBr is removed, so that the developed part is fixed.

Soda also has strong reducibility, which can reduce chlorine and other substances.

Na2S2O3+4cl2+5h2o = = = H2SO4+2nac+6hcl, so it can be used as a dechlorination agent for cotton fabric after bleaching. Similarly, iodine stains on fabrics can also be removed with it.

In addition, baking soda is also used for tanning leather, electroplating and extracting silver from ores.