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Chemistry Forums for Students => Inorganic Chemistry Forum => Topic started by: CrazyGoat on January 05, 2021, 12:28:04 AM

Title: drying zncl2
Post by: CrazyGoat on January 05, 2021, 12:28:04 AM

 This friend of mine says that if you try to dry ZnCl2 in a flask, with a heat gun, and under a vacuum, it's going to yield Zn(OH)Cl, not ZnCl2, and therefore we must carry it from the bottle to the flask into a vacuum chamber that we don't have at this moment. 
 Instead, I say to him, that the moisture that the powder is going to gain in "its move" (carrying), from the bottle to the flask, is not going to be enough for a significant loss, I say that the OH and CL are going to be sucked by the pump leaving pure and dry ZnCl2 without major inconveniences.
Whom do you think is right?

Thank you.

Title: Re: drying zncl2
Post by: AWK on January 05, 2021, 01:28:05 AM
Anhydrous ZnCl2 is hygroscopic. If it is strongly heated, it will obviously partially hydrolyze. Basic zinc chloride is practically obtained from the monohydrate.
There are many methods for the preparation of anhydrous ZnCl2. In the laboratory, the simplest method is to decompose the water contained in ZnCl2 or Zn(OH)Cl by reaction with SOCl2.
Title: Re: drying zncl2
Post by: CrazyGoat on January 05, 2021, 02:02:38 AM

"it will obviously partially hydrolyze"

 That is what I mean, don't care to lose up to 50% heating it, if this will completely dry it into the flask.

 The bottle we have is anhydrous and I will transfer it quickly from bottle to flask.
 Then heat it generously under a vacuum to remove the resulting gases along with the flask moisture.

 THANK YOU for your kind answerer :-*
Title: Re: drying zncl2
Post by: CrazyGoat on January 05, 2021, 05:06:54 PM
 Sorry, but this above stills been a question.

It wasn't my intention to do a conclusion or statment (excuse me if it sounded like that)

I am still doubtful about if this way of drying ZnCl2 could have more downsides other than the material loss.

 Thank you.
Title: Re: drying zncl2
Post by: AWK on January 06, 2021, 12:02:34 AM
Drying is the removal of water from the dried substance. Most often it is related to the weight loss of the dried sample based on the hydrate stoichiometry.
Drying the zinc chloride monohydrate should result in a weight loss of about 12%, and in fact, the weight loss is close to 24% due to the chemical reaction taking place. However, the dried sample still contains the same amount of zinc.
In the case of moist anhydrous zinc chloride, the weight loss will depend on the moisture content.
Many reactions require perfectly anhydrous zinc chloride and must then be dehydrated by a suitably effective method.
Title: Re: drying zncl2
Post by: CrazyGoat on January 06, 2021, 02:24:31 PM
 I am sorry but I still don't get why the discussed method is not an effective method. The reaction I am seeking is, as you wrote, one that requires perfectly anhydrous zinc chloride. Drying the slightly moist zncl2 under a vacuum is my easier option at this moment.
Title: Re: drying zncl2
Post by: wildfyr on January 06, 2021, 06:32:35 PM
ZnCl2 heated in the presence of water will not just boil off some of the water, it will also cause some of the ZnCl2 to react and make zinc hydroxide which will contaminate your sample, and can't be removed. Further heating that probably would give zinc oxide.

So basically, its easier to simply make fresh ZnCl2 than it is to try to somehow sort it from water.
Title: Re: drying zncl2
Post by: AWK on January 07, 2021, 03:51:45 AM
All this discussion is unnecessary. You do not specify the type of reaction, reaction conditions, solvent. You are asking about a way to effectively dehydrate zinc chloride. In the end, it turns out experimentally in your laboratory that strong heating under a vacuum is sufficient for your reaction. This means that the zinc oxide contamination does not interfere with your reaction.
In this drying method, you should try to answer two questions: 1. To what extent does zinc chloride hydrolysis occur? 2. Which reaction of thermal decomposition of basic zinc chloride (there are two possible) actually takes place?
Answers to both questions can be found in the literature (hint - thermogravimetric research).