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Offline Rutherford

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Mn2+
« on: June 25, 2012, 10:17:42 AM »
From the wikipedia page:
4th analytical group of cations
The fourth group of cations include Zn2+, Ni2+, Co2+, and Mn2+. This group is determined by the addition of ammonium chloride, ammonium hydroxide, and hydrogen sulfide gas to the solution of the salt. A colored precipitate indicates Mn2+...

Is is really neccessary to add hydrogen sulfide gas or I can add it as a liquid, because I don't know how to add it as a gas, or is there any better way to determine Mn2+ ions?

Offline AWK

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Re: Mn2+
« Reply #1 on: June 25, 2012, 10:32:17 AM »
Ther best method use oxidation to HMnO4 with NaBiO3 (the best reagent), Pb3O4 or PbO2 in nitric acid. Moreover this can be done using the whole mixture of cations without separation any of them.
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Offline Borek

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Re: Mn2+
« Reply #2 on: June 25, 2012, 10:43:47 AM »
From what I know at least since seventies instead of gaseous H2S everyone uses thioacetamide.
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Offline Rutherford

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Re: Mn2+
« Reply #3 on: June 25, 2012, 11:02:40 AM »
I am preparing for the next level (more ions) of qualitative inorganic analisys. I need to make a chart, but I got stuck on the IVth group: Mn2+ and Zn2+. Unfortunately, I won't be allowed to use thioacetamide and as I found out, neither H2S is allowed.

Offline AWK

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Re: Mn2+
« Reply #4 on: June 25, 2012, 11:12:44 AM »
The fourth group of cations include Zn2+, Ni2+, Co2+, and Mn2+. This group is determined by the addition of ammonium chloride, ammonium hydroxide, and hydrogen sulfide gas to the solution of the salt. A colored precipitate indicates Mn2+...[/sub]
NiS and CoS are black. How can you see white or pale pink precipitate?
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Offline Rutherford

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Re: Mn2+
« Reply #5 on: June 25, 2012, 11:54:34 AM »
From the fourth group I only need to know the determination processes for Mn2+ and Zn2+ for the test. I need to find another way for proving those catinos because I won't be able to use H2S(g), so I'm stuck now.

Offline AWK

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Re: Mn2+
« Reply #6 on: June 26, 2012, 04:59:28 AM »
I told you about Mn2+ test.
How this cations react with an excess of NaOH?
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Offline Rutherford

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Re: Mn2+
« Reply #7 on: June 26, 2012, 05:59:29 AM »
Thanks, good one, white precipitate soluble in acids not in excess of NaOH.
Now, I need only for the Zn2+ cation something good.

Edit: Found similar for Zn2+ only it will dissolve in  excess of NaOH. Ca2+ and Mg2+ make insoluble hidroxydes witn NaOH, too, but they won't dissolve in excess of NaOH, right?
« Last Edit: June 26, 2012, 06:55:11 AM by Raderford »

Offline AWK

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Offline Rutherford

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Re: Mn2+
« Reply #9 on: June 26, 2012, 03:13:12 PM »
I found a very nice way for Mn2+ with HNO3 and PbO2. Tomorrow I should finish the whole list.

Offline Rutherford

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Re: Mn2+
« Reply #10 on: June 26, 2012, 03:21:56 PM »
http://faculty.coloradomtn.edu/jeschofnig/class/class_jeschof/ch2-lb8.htm
Is that reaction characteristic only for Zn2+ and not for the alkali and earth-alkali metals, because I'm planning to test their presence right after Zn?

Offline AWK

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Re: Mn2+
« Reply #11 on: June 27, 2012, 01:49:24 AM »
Supernatant after treatment with an excess of NaOH should be used.
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Offline Rutherford

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Re: Mn2+
« Reply #12 on: June 27, 2012, 04:38:20 AM »
I will have plenty of the unkown salt so I can make a new solution. Ca, Ba, Mg, Na and K don't react with K4[Fe(CN)6]?

Offline AWK

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Re: Mn2+
« Reply #13 on: June 27, 2012, 04:55:42 AM »
https://www.msu.edu/~grahamm9/General%20Solubility%20Rules%20for%20Ionic%20Cmpds.%20in%20H20.htm
There are better methods for qualitative analysis of Ca, Ba, Mg cations than using ferrocyanides.
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Offline Rutherford

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Re: Mn2+
« Reply #14 on: June 27, 2012, 05:11:29 AM »
I didn't mean to determine them with ferrocyanides (I am planning to do it on fire), but I don't understand how to be sure if there is Zn2+ present in the solution or one of the earth alkali metals if they all make white precipitates with ferrocyanides. A mistake could happen.

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