硫代硫酸鈉是硫代硫酸（H2S2O3）的鈉鹽，硫代硫酸的結構簡式可寫作HO—SSO—OH，可看作硫酸（HO—SO2—OH）中的一個氧原子被硫原子取代后得到的化合物，自由的硫代硫酸是不穩定的，易分解為S、SO2和H2O，但硫代硫酸的鹽可以是穩定的。
Sodium thiosulfate is the sodium salt of thiosulfuric acid (h2s2o3). The structural formula of thiosulfuric acid can be written as ho-sso-oh, which can be regarded as a compound obtained after an oxygen atom in sulfuric acid (ho-so2-oh) is replaced by a sulfur atom. Free thiosulfuric acid is unstable and easy to decompose into s, SO2 and H2O, but the salt of thiosulfuric acid can be stable.
含有5個結晶水的硫代硫酸鈉，即Na2S2O3·5H2O，也就是俗稱的“大蘇打”或者“海波”，是一種常見的工業品或者化學試劑。硫代硫酸根離子有較強的配位能力，能與一價銀離子Ag+生成穩定的絡離子[Ag(S2O3)2]3-，其穩定常數Kf比常見的銀氨絡離子[Ag(NH3)2]+高好幾個數量級，因此過去常作為照相底片或者相紙的定影劑，以溶解底片或者相紙上未感光的鹵化銀（以溴化銀為主）：→
Sodium thiosulfate containing five crystal waters, namely Na2S2O3 · 5H2O, commonly known as "baking soda" or "Haibo", is a common industrial product or chemical reagent. Thiosulfate ion has strong coordination ability and can form a stable complex ion [Ag (s2o3) 2] 3 - with monovalent silver ion Ag +, and its stability constant KF is several orders of magnitude higher than the common silver ammonia complex ion [Ag (NH3) 2] +. Therefore, it used to be used as a fixing agent for photographic negatives or paper to dissolve the non photosensitive silver halide on negatives or paper (mainly silver bromide): →
硫代硫酸鈉有較強的還原性，可以與鹵素單質反應，其中與碘的反應是定量的：
Sodium thiosulfate has strong reducibility and can react with halogen, in which the reaction with iodine is quantitative:
是連四硫酸鈉，即連四硫酸（H2S4O6）的鈉鹽，連四硫酸的結構簡式是HO—SO2—S—S—SO2—OH，分子中存在S—S—S—S硫鏈。該反應在分析化學中用于測定碘的含量，滴定時可用淀粉作為指示劑。用5％的硫代硫酸鈉溶液浸漬口罩，可防護低濃度的氯氣，對皮膚的刺激性要比NaOH等強堿小得多。
Sodium tetrasulfate, Tetrasulfuric acid The structural formula of (h2s4o6) sodium salt and tetrasulfuric acid is ho-so2-s-s-so2-oh, and there is s-s-s sulfur chain in the molecule. This reaction is used to determine the content of iodine in analytical chemistry, and starch can be used as an indicator in titration. Dipping the mask with 5% sodium thiosulfate solution can protect the low concentration of chlorine, and the irritation to the skin is much less than that of strong bases such as NaOH.
硫代硫酸鈉還可以作為氰化物中毒的劑，在體內可以將劇毒的氰離子CN-轉化為毒性很低的硫氰酸根離子SCN-，以解除CN-的毒性。
Sodium thiosulfate can also be used as an antidote to cyanide poisoning. In vivo, it can convert highly toxic cyanide ion CN - into very low toxic thiocyanate ion SCN - to relieve the toxicity of CN -.
·5H2O加熱到約48℃時，Na2S2O3溶解在自身的結晶水中，成為溶液，繼續加熱則逐漸失去結晶水得到無水物，如果再繼續高溫加熱，Na2S2O3開始分解，分解產物中有少量單質硫成為硫蒸氣放出，遇空氣可能燃燒發出藍色火焰，分解產物中還含有SO2等氣體，有強烈的刺激性氣味，因此工業品硫代硫酸鈉也要注意防火。
·When 5H2O is heated to about 48 ℃, Na2S2O3 will dissolve in its own crystal water and become a solution. If it continues to heat, it will gradually lose the crystal water to obtain anhydrous matter. If it continues to heat at high temperature, Na2S2O3 will begin to decompose, and a small amount of elemental sulfur in the decomposition product will be released as sulfur vapor. In case of air, it may burn and emit blue flame, and the decomposition product also contains SO2 and other gases, There is a strong pungent smell, so the industrial sodium thiosulfate should also pay attention to fire prevention.
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