Identify the metal which undergoes these reactions

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Discussion Overview

The discussion revolves around identifying a specific metal based on a series of chemical reactions and their properties, including precipitation and solubility. Participants explore the characteristics of various metals and their compounds, particularly focusing on zinc, aluminum, magnesium, and tin, in the context of homework-related chemistry problems.

Discussion Character

  • Homework-related
  • Debate/contested
  • Exploratory

Main Points Raised

  • One participant notes that with excess NaOH, a white precipitate dissolves, suggesting it could be zinc hydroxide or aluminum hydroxide, but is uncertain about how to differentiate between them.
  • Another participant points out that lead sulfide is black, which eliminates lead as a possibility.
  • A participant eliminates magnesium based on its inability to form a precipitate as a hydroxide, but later questions their understanding of solubility rules regarding Group II hydroxides.
  • There is confusion about the role of H2S in the reactions, with a participant questioning whether it acts as a catalyst.
  • One participant asserts that aluminum sulfide cannot be precipitated from water solutions due to its decomposition upon contact with water.
  • Another participant concludes that zinc is the likely answer based on the properties discussed, but this conclusion is not universally accepted as definitive.

Areas of Agreement / Disagreement

Participants express differing views on the identification of the metal, with some supporting zinc as the answer while others raise concerns about the properties of aluminum and magnesium. The discussion remains unresolved regarding the definitive identification of the metal.

Contextual Notes

There are limitations in the understanding of solubility rules and the behavior of metal sulfides and hydroxides, which may affect the conclusions drawn by participants.

TT0
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Homework Statement


Screen Shot 2016-07-02 at 11.23.24 AM.png


Homework Equations

The Attempt at a Solution


The only thing that helped me was that with excess NaOH, the white precipitate dissolves. The only compounds I know that do this are zinc hydroxide and aluminium hydroxide. However, I don't know how the other reactions will help me decide between the two. Could someone explain this?

Cheers!
 
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Check properties of the metals involved. For example - last step is clearly precipitation of the sulfide. What color is a lead sulfide?
 
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Lead sulfide is black according to google images. So I guess it is eliminated. Magnesium definitely wouldn't be it because it won't form a precipitate as a hydroxide.

This leaves us with zinc, aluminium and tin. Googling each of the sulfides, I can eliminate tin sulfide as it is not white. I don't really know where to go from here, I tried to look at the properties of the metals but I still don't know. In the last reaction, why is H2S on the top and NaOH on the bottom. Is the H2S a catalyst? I think knowing this might help.

Cheers!
 
TT0 said:
Magnesium definitely wouldn't be it because it won't form a precipitate as a hydroxide.

Check that.
 
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I see, my solubility rules was wrong. Group II hydroxides are only slightly soluble. I got confused because they are also strong bases, yet they are only slightly soluble?

Magnesium sulfide is soluble and forms hydrogen sulfide and magnesium hydroxide. But as there are already hydrogen sulfide and magnesium hydroxide, I guess ti will precipitate. So magnesium is the answer?

Thanks!
 
No, as magnesium sulfide is soluble.
 
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In the first 3 reactions, the amphoteric reactions are happening right? This leaves zinc and aluminium as they are the ones that display these properties. When I googled zinc and aluminium sulfide, it seems both are white compounds. How do you differentiate between them?

Thanks!
 
I don't think you can precipitate aluminum sulfide from water solutions - it decomposes on contact with water.
 
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I see, so the answer is zinc. Thanks for all the help!
 

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