The preparation of precipitated elemental sulfur by reaction of sodium thiosulfate with acid is a common method for preparing a small amount of elemental sulfur. The purity of sulfur obtained by this method is higher, and it is easy to produce crystalline sulfur (S8) powder. Unlike sublimed sulfur, which is often mixed with amorphous sulfur polymers, the reaction performance is better. It can be used as a raw material for some synthesis or to remove mercury leaks (such as accidentally breaking mercury thermometers, thermometers, etc.).
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The principle of this method is very simple, sodium thiosulfate reacts with acid to produce thiosulfuric acid (H2S2O3), and thiosulfuric acid is unstable and decomposed:
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H2S2O3 → H2SO3 S↓
H2SO3 → H2O SO2↑
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In fact, the decomposition reaction of thiosulfuric acid is very complex, the above reaction is only a rough description of the reaction principle, the total reaction in the middle school chemistry stage can be written as:
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H2S2O3 = H2O S ↓ SO2 ↑
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The sodium thiosulfate solution is applied to the skin surface or clothing, and then applied with about 2% of the medicinal diluent hydrochloric acid, can slowly release sulfur and sulfur dioxide, which is used to kill scabies and treat scabies (this method must be used under the guidance of a doctor).
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When preparing, sodium thiosulfate is generally easy to buy sodium thiosulfate pentahydrate crystal, which is commonly known as \"baking soda\" or \"sea wave\
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1, this reaction generates SO2, has a strong irritation, so it is best not to react in an open container, should react in a flask, distillation flask or conical flask, and the generated SO2 is exported with a catheter, and then absorbed with Na2CO3 solution (do not use NaOH solution absorption, SO2 absorption with NaOH solution is easy to cause suction). This can not only avoid polluting the air, but also recover Na2SO3 or NaHSO3.
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(2) Do not inject concentrated acid or diluted uncooled acid directly into solid sodium thiosulfate or sodium thiosulfate concentrated solution, which may cause a quite violent reaction, a large amount of escape SO2 or even punch.
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3. The amount of sodium thiosulfate and acid should be calculated in advance. If the raw material is sodium thiosulfate pentahydrate crystal, it may be further converted into quality, and the amount of acid should be slightly excessive. If the use of phosphoric acid and other medium strong acids, the calculation can only be calculated according to the ionization of the first hydrogen ion, because the Ka2, Ka3 and so on of these medium strong acids are very small, the actual contribution of the second more than ionized hydrogen ions to the reaction is very small, basically negligible, for example, the reaction of phosphoric acid and sodium thiosulfate can be written as:
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Na2S2O3 2H3PO4 → 2NaH2PO4 S↓ SO2↑ H2O
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4. Sodium thiosulfate should be dissolved with an appropriate amount of water first, prepared into a concentrated solution of sodium thiosulfate, and then slowly add the acid that has been diluted and cooled, hydrochloric acid can be diluted to 1:1, sulfuric acid can be diluted to 1:5, phosphoric acid can be diluted to 1:2, sodium bisulfate solution can be prepared into 3mol\/ L-4mol \/L, and it is best to slowly add it with a liquid separation funnel if conditions are available. The concentration of sodium thiosulfate solution and acid should not be too high, otherwise the sodium salt such as sodium chloride and sodium sulfate generated is easy to crystallize out, and it is difficult to separate from sulfur.
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5, after adding dilute acid, if the sodium thiosulfate solution and dilute acid have been fully cooled, it may be delayed for a period of time (a few seconds) to see that the liquid begins to become cloudy, which is normal, because the decomposition of thiosulfuric acid takes a certain time, but the liquid begins to become cloudy far from indicating that the reaction has been fully carried out, at this time it should be slightly hot liquid, with the escape of SO2, The reaction will proceed more and more fully, and the increase in temperature will also facilitate the aging of sulfur precipitation to obtain crystalline sulfur.
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6, heating reactants, do not need to heat to the liquid boiling, only need to see the SO2 bubbles gradually emerge, SO2 bubbles basically no longer escape after you can stop heating, too high heating temperature will make the precipitated sulfur (usually ruse sulfur microcrystals) into a needle monoclinic sulfur crystal, but does not affect the use of.
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7, SO2 escape after the basic completion, stop heating, to be sulfur settlement, the settlement of sulfur should be gathered at the bottom of the container, the upper liquid is basically transparent, if the liquid is still obviously turbidity, indicating that sulfur precipitation aging is not sufficient, and even sulfur sol generation, can be reheated for a period of time and fully static cooling for a period of time.
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8, with the pouring method or filtration method to separate the precipitation of sulfur, and then wash with water 2-3 times, each washing should try to wait for the full settlement of sulfur, in order to reduce the loss, you can also use warm water washing, and finally can get quite pure sulfur. This sulfur is highly reactive for many reactions, such as the preparation of polysulfides.
It is mainly prepared by heating salt and concentrated sulfuric acid, starting with heating, and then stopping heating, because the reaction is exothermic.
NaCl+H2SO4(concentrated)→HCl↑ NaHSO4
This reaction is also used in the laboratory to produce hydrogen chloride and strong acids to produce weak acids.
(In fact, such items belong to the basic items of inorganic substances, generally if the experiment is directly purchased, the cost of production and use is too high, and the yield is not ideal)
It is mainly prepared by heating salt and concentrated sulfuric acid, starting with heating, and then stopping heating, because the reaction is exothermic. NaCl+H2SO4(concentrated)→HCl↑ NaHSO4 This reaction is also used in the laboratory to produce hydrogen chloride and strong acids to produce weak acids. (In fact, such items belong to the basic items of inorganic substances, generally if the experiment is directly purchased, the cost of production and use is too high, and the yield is not ideal)