Aluminum potassium sulfate preparation and crystal growth
One, the purpose of the experiment
1 understand the principle and process of producing aluminum sulfate;
2 further understanding of the Al and Al (OH) 3 sexes;
3 education principles and methods of crystals from solution.
Two, the experimental principle
The sulfate aluminum with alkali metal (K2SO4) forming aluminum potassium sulfate salt.
Aluminum potassium sulfate (K2SO4 · Al2 (SO4) 3 · 24H2O) commonly known as alum, it is a kind of colorless crystals, Yi Rong in the water, and the hydrolysis of Al (OH) 3 casse. It has a strong absorption performance, aluminum salt industry is important, as water purifying agent, filling agent in papermaking etc..
This experiment using aluminum dissolved in sodium hydroxide solution, four hydroxy aluminum acid sodium production of soluble metal aluminum, otherimpurities are insoluble, filter to remove impurities. Then using H2SO4 to regulate the pH value of the solution for 8-9, namely Al (OH) 3 precipitate,separation, adding H2SO4 in the precipitation, the Al (OH) 3 into Al2 (SO4) 3,and then made into Al2 (SO4) 3 crystals, Al2 (SO4) 3 crystal and K2SO4 crystalrespectively into saturated solution, mixing with alum generated. The reaction is as follows:
2Al + 2NaOH + 6H2O = 2Na[Al (OH) 4] + 3H2
[Al (OH) 4]+ H+ = Al (OH) 3 + H2O
2Al (OH) 3 + 3H2SO4 = Al2 (SO4) 3 + 6H2O
Al2 (SO4) 3 + K2SO4 + 24H2O = K2SO4 · Al2 (SO4) 3 · 24H2O
Cultivation of alum crystal: when there is K2SO4 · Al2 (SO4) 3 · 24H2O crystal precipitation, filtering to obtain crystal, choose structured as a seed, put in the filtrate, the upper dish, let the solution of natural evaporation, crystallization will gradually grow up, become a large single crystal, crystal has eight surface morphology. In order to make the seeds grow large single crystal, it is important not to solution temperature change is too big, make water slow evaporation. In addition to grow large crystals, crystal system can also be generated with the nylon rope, suspended in solution. Such crystals in the growth rate is not affected, the crystals formed more rules.
Three, experimental equipment
Apparatus and materials: beaker, electronic scales, funnel, the evaporating dish,alcohol lamp, three tripod, asbestos, matches, glass funnel, cylinder, filter paper,pH paper, nylon line.
Reagents: Al chip (C.P), NaOH (C.P), K2SO4 (C.P), H2SO4 (3mol · L - 1, 1:1),BaCl2 (0.1 mol · L - 1).
Four, the experimental steps
1.Al (OH) 3 generation
Take 2.3 grams of NaOH solid, into a 200mL beaker, add 30mL distilled water solution. Take 1 grams of aluminum scrap, in batches into the solution (reaction,prevent spills, should be carried out in a fume hood), to no longer have bubbles,indicating the reaction is completed, and then adding distilled water, the volume is about 40mL, filtration. The filtrate into a 200mL beaker, heated to boiling, withcontinuous stirring, add 3mol · L - 1H2SO4, the solution of pH 8 - 9, continue to stir boiled a few minutes, and then filtration, washing and precipitation with boiling water, until the washing liquid pH value reduced to about 7, dry.
2.Al2 (SO4) 3 preparation
The prepared Al (OH) 3 into the beaker, under continuous stirring, adding 1:1,H2SO4, and water bath heating. When the solution became clear, stop adding sulfuric acid, Al2 (SO4) 3 solution. The concentrated solution for the 1/2 of the original volume, removed, water cooling to room temperature, the crystallization,filtration, the crystal blot with the filter paper, weighing.
Culture and crystal 3 alum system
The weighing of the aluminum sulfate crystal is arranged on the small beaker,with saturated solution at room temperature. The other weigh K2SO4 solid, alsowith the same volume of saturated solution, and then an equal volume of twosaturated solution phase mixing, stirring evenly. After placement, there will bealum crystal precipitation. Select the filter, structured as a seed, put in thefiltrate, the upper dish, let the solution of natural evaporation, crystallization will gradually grow up, become a large single crystal, crystal has eight surfacemorphology.
In order to make the seed generation of large single crystal, it is important not tosolution temperature change is too big, make water slow evaporation. To generate a large crystal, crystal system can also be generated with the nylon rope, suspended in solution. Such crystals in the growth rate is not affected.
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