freezing point of sulfuric acid
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Why does the lower the concentration of sulfuric acid, the lower its freezing point? Anyone who knows please give me some advice.
Let’s look back at physical chemistry to review the past and learn something new!
In fact, you can think about it this way, if the concentration of sulfuric acid is infinitely dilute, it will become water.
In that case, the lowest freezing point is 0 degrees, and the freezing point of sulfuric acid should be above 0 degrees. So when dilute sulfuric acid is heated, they don't solidify. So it should be that the higher the concentration, the lower the freezing point! ~
Because sulfuric acid can be seen as composed of 3+1 = 4 simple eutectic phase diagrams. H2O H2SO4·4H2O H2SO4·2H2O H2SO4·H2O H2SO 4H2SO4·H2O, H2SO4·2H2O and H2SO4·4H2O are three stable compounds. The temperature-composition diagram is as follows. It can be seen as composed of 3+1 = Made up of 4 simple eutectic phase diagrams. Ⅰ— solution, Ⅱ— H2O (s) + solution, Ⅲ — H2SO4·4H2O (s) + solution IV— H2SO4 ·4H2O (s) + solution, Ⅴ— H2SO4 ·2H2O (s) + solution Ⅶ— H2SO4·2H2O (s) + solution, Ⅷ— H2SO4·H2O (s) + solution Ⅸ— H2SO4 (s) + solution, Ⅻ′—H2SO4·H2O (s) + H2SO4 (s) It can be seen from the figure: ①Concentrated sulfuric acid is 98%, with a very low crystallization temperature of only 0.25°C. As a product output, it is easy to crystallize out H2SO4 solid and block the pipeline. Sulfuric acid with a concentration of 92.5% (commonly known as 93% acid) has a freezing point of about 238.2K, which is -35°C. It is safe for product transportation and will not encounter the problem of pipeline clogging. ② The freezing point of about 90% sulfuric acid changes greatly with concentration. 93% acid - -35°C, And 91% acid - 17.3℃, 89% acid - 4℃. It is easy for solids to break out in winter. Therefore, the same pipeline cannot be used to output sulfuric acid of different concentrations in winter to avoid pipeline blockage due to concentration changes. The freezing point of concentrated sulfuric acid: 10.35℃(100%), 3℃(98%), -32℃(93%), -38℃(78%), -44℃(74%), -64℃(65%). Therefore, more than 98% of enterprises that need to use concentrated sulfuric acid must pay special attention to heat preservation.
What you said is incorrect. Sulfuric acid shows a wavy curve as the concentration (mass concentration) increases. Note that the condensation point is the highest at 89.1% and the lowest at about 30%.
Please take a look at the physical chemistry. What you said is incorrect. As the concentration of sulfuric acid increases, its freezing point appears as a wavy line, which sometimes rises and sometimes falls. It is not a positive function.
I still don’t quite understand. I’m stupid. Can you explain it more simply?
The next information on sulfuric acid is very detailed and has diagrams. This section has it.
The post on the 5th floor makes it very clear. Check the information and learn to read the photos, and you will understand it yourself.