Questions about crystallization ( )
Thread Content
During the experiments these past two days, there was a solution in which the sodium oxide content ranged from 100–160 g/L, and the silica content ranged from 52–110 g/L. The solution mainly contained sodium hydroxide and sodium silicate, with small amounts of sodium carbonate and sodium aluminate present as well. When exposed to air at room temperature for one night, a large amount of crystals form the next day; these crystals dissolve again when exposed to high temperatures. I would like to ask everyone: what are these crystals? Or what impurities could reduce the solubility of sodium hydroxide or sodium silicate?
Personal guesses: 1. It’s unclear whether saturation has occurred; the evaporation of water leads to a decrease in solubility, resulting in the formation of crystals. 2. It’s possible that when these substances are placed together for an extended period of time, compounds containing crystal water will form. 3. A reaction has taken place with carbon dioxide in the air; this can be determined by weighing the samples in a sealed container using an analytical balance. Check again the evaporation rate of moisture at room temperature, and check the weight. 4 Whether these substances can produce flocculation.
First: The solution is definitely not saturated. Second: It was only left there for one night, and I measured that very little water evaporated during that time – only 1.97%. Third: The only reaction that could occur is the formation of sodium carbonate, which has a high solubility at room temperature. Fourth: It’s also unlikely, because no crystallization occurs when the solution is kept away from air!
Na2O reacts with the water in the NaOH solution to produce NaOH and H2O. As a result, the amount of water decreases while the amount of NaOH increases. Since it was originally a saturated solution, the decrease in water volume inevitably leads to the precipitation of NaOH. Sodium hydroxide is highly soluble in water, and its solubility increases as the temperature rises; therefore, raising the temperature causes it to dissolve again
I checked the Lan’s Chemical Handbook; the solubility of sodium hydroxide at 10 degrees Celsius is 51 g/100 g. You can calculate what the corresponding concentration of sodium oxide is This reason was ruled out from the start! It can be preliminarily determined that the impurities on the sampling cup are the cause of the crystallization; I cleaned the sampling cup with ultrasonic waves, and no crystallization occurred the next day. Now I would like to ask everyone what kind of impurities are responsible for the crystallization of sodium hydroxide or sodium silicate