Cultivation and preparation of potassium aluminum sulfate crystals

First, the purpose of the experiment

1 . Learn from the principle of the preparation of aluminum and aluminum potassium sulfate process ;

2 . Further understanding of Al and Al (OH) 3 sexes ;

3 . Principles and methods of learning in the crystals from the solution.

Second, the experimental principle

Aluminum sulfate with an alkali metal sulfate (K2SO4) and potassium aluminum sulfate and generated salts.

Aluminum potassium sulfate (K2SO4 · Al2 (SO4) 3.24 H2O) , commonly known as alum, which is a colorless crystals , soluble in water and hydrolysis of Al (OH) 3 gel precipitation. It has strong adsorption properties is an important aluminum industry, can be used as purifying agent , paper filling agent for many purposes .

The experiment was dissolved in sodium hydroxide solution using the aluminum metal , aluminum hydroxy generated four soluble sodium aluminum impurities in the remaining insoluble impurities removed by filtration . H2SO4 followed by adjusting the pH of the solution was 8-9 , i.e. with Al (OH) 3 precipitate , after separation , the precipitate was added H2SO4 , that the conversion of 3 Al2 (SO4) 3 Al (OH), then formed Al2 (SO4) 3 crystals, Al2 (SO4) 3 K2SO4 crystals and crystals were saturated solution , after mixing, have generated alum . About 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) 3.24 H2O

Alum monocrystalline culture : When there K2SO4 · Al2 (SO4) 3.24 H2O after precipitation of crystals , the crystal was filtered , structured as a selected seed crystals in the filtrate, and covered with a watch glass , allowing the natural evaporation of the solution , crystallization will gradually grow to become a large single crystal , single crystals with octahedral crystal form . The seed crystal to be grown as a single crystal , it is important not to change the temperature of the solution is so large that the water solution was slowly evaporated. Also to be grown crystals can also be generated on the crystal system of nylon rope , suspended in solution. Such crystal growth rate is not affected in all respects , to generate a more regular crystals .

Third, experimental supplies

Instruments and Materials : beakers, electronic scales, Buchner funnel , evaporating dish , alcohol lamp , tripod, asbestos network , matches, glass funnel , graduated cylinder , filter paper , pH test strips, nylon cord.

Reagents : Al crumbs (CP), NaOH (CP), K2SO4 (CP), H2SO4 (3mol · L-1, 1:1), BaCl2 (0.1 mol · L-1).

Fourth, the experimental procedure

1 . Al (OH) 3 is generated

Weigh 2.3 g of solid NaOH , placed in 200mL beaker, add 30mL distilled water . Weigh 1 g of aluminum shavings in batches into the solution ( violent reaction against spills , should be carried out in a fume hood ) , to no more bubbles , and the reaction is completed, then add distilled water to bring the volume to approximately 40mL , filtration . The filtrate was transferred to 200mL beaker and heated to boiling , under continuous stirring , a solution of 3mol · L-1H2SO4, the pH of the solution is 8-9 , and stirring was continued for several minutes to boil , then suction filtered and the precipitate washed with boiling water until the pH value of the washing liquid is reduced to about 7 dry.

2 . Preparation of Al2 (SO4) 3 in

The resulting Al (OH) 3 into a beaker with constant stirring , was added 1:1 H2SO4, and water bath . When the solution becomes clear, stop the addition of sulfuric acid to give Al2 (SO4) 3 solution . The solution was concentrated to one half of the original volume , removed, cooled to room temperature and washed with water until crystallization was complete, filtered, the crystals were blotted dry with filter paper and weighed .

3 . Preparation and training of large crystals of alum

Aluminum sulfate crystals weighed into a small beaker, dubbed a saturated solution at room temperature. Another Weigh K2SO4 solid , also dubbed the same volume of a saturated solution , and then an equal volume of a saturated solution of the two -phase mixture, stirring well. After standing , alum crystals will be precipitated. Filtration , elected structured as a seed , on the filtrate , cover the surface of the pan, allow the solution to natural evaporation, crystallization will gradually grow to become a large single crystal , single crystals with octahedral crystal form .

In order to generate a large single crystal seed , it is important not to change the temperature of the solution is so large that the water solution was slowly evaporated. To generate large crystal , the crystal can also be generated on the system nylon rope suspended in the solution. Thus in all aspects of the crystal growth rate is not affected .