Gallic Acid monohydrate, the chemical name is 3,4,5-Trihydroxybenzoic acid, and the molecular formula is C7H6O5. It is a polyphenolic organic compound, white to light yellow needle-like crystals, odorless, and slightly acidic. It turns brown when exposed to light. Heating to 100～120℃ will lose crystal water. 1G is soluble in 87ml water, 3ml boiling water, 6ml ethanol, 100ml ether, 10ml glycerol, 5ml acetone, and is almost insoluble in benzene, chloroform and petroleum ether. The relative density is 1.694. Melting point: 235～240℃ (decomposition).
Application：
1. It is used as depolarizer in electrochemical analysis; for reducing phosphomolybdory acid; for testing antimony, barium, bismuth, calcium, and copper, etc .; used to determine phosphorus, nitrite, silver, and titanium, etc. ;
2. It can also form blue black precipitation with ferric ions, which is the raw material of blue black ink.