Stoichiometry: Identify the metal and formula of it

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Discussion Overview

The discussion revolves around identifying a lanthanide metal based on its reaction with hydrochloric acid (HCl) and the resulting product. Participants explore the stoichiometry involved in the reaction and the implications of the mass changes observed during the experiment.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant presents a reaction equation involving a lanthanide metal (M) and HCl, questioning the necessity of including hydrogen gas (H2) in the equation.
  • Another participant suggests ignoring H2 and focusing on the metal chloride (MCln) to simplify the problem-solving process.
  • Some participants propose that samarium (Sm) is the unknown metal based on their calculations, but they express uncertainty about the correctness of this identification.
  • There is a discussion about the fate of hydrogen during the reaction, with participants noting that it escapes and is not represented in the final equation.
  • One participant emphasizes that the stoichiometric relationship between the metal and its chloride product is the critical aspect of the equation, while other components are deemed unnecessary for solving the problem.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the necessity of including hydrogen in the reaction equation, and there are differing opinions on the identification of the metal, with some suggesting samarium while others remain uncertain.

Contextual Notes

Participants acknowledge that the amount of HCl used is not critical as long as it is in excess, and they highlight that the focus should remain on the stoichiometric relationships rather than extraneous details.

Sho Kano
Messages
372
Reaction score
3

Homework Statement


All of the lanthanide metals (La through Lu) react with HCL to form compounds having eithe the formula MCl2, MCl3, MCl4, (where M represents the metallic element). Each metal forms a single compound. A chemist has a 0.250g sample of a lanthanide metal, and she wishes to identify the metal. She reacts the metal with excess HCl and obtains 0.427g of the product. Based on this information, identify the metal and write the chemical formula of the product.

Homework Equations

The Attempt at a Solution


I'm not sure the below equation is correct. I originally wrote the equation without the H2, but it did not seem to be right with conservation of mass.
M + HCL —> MCl2 (or MCl3, MCl4) + H2
Basically, if the H2 does belong there, then I'd just have to guess MCl2, 3, or 4, then balance the equation, then randomly guess an element right? Seems like a lot of work.
 
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Sho Kano said:
and obtains 0.427g of the product.
Sho Kano said:
2, 3, or 4, then balance
 
I can't see anything on your post
 
MCln is all you need; ignore the H2, and just start cutting and trying.
 
Bystander said:
MCln is all you need; ignore the H2, and just start cutting and trying.
I'm getting Sm as the unknown metal; is that right?
 
Samarium? Mental arithmetic checks out.
 
Bystander said:
Samarium? Mental arithmetic checks out.
Awesome. What happens to the hydrogen though?
 
Sho Kano said:
What happens to the hydrogen though?
It "fizzes" away up the chimney/hood/exhaust system.
 
Bystander said:
It "fizzes" away up the chimney/hood/exhaust system.
I mean why is it not represented in the chemical equation
 
  • #10
"M" + nHCl = (n/2)H2 + "M"Cln; it is.
 
  • #11
Hydrogen is present in the reaction equation and we can even easily calculate its amount. We just ignore it as it is not necessary for solving the problem (just like the amount of HCl doesn't matter, as long as there is enough of it).

The only part of the equation that matters is

Sm → SmCl3

It preserves the only important information here - stoichiometric ratio between Sm and SmCl3. When solving this particular problem everything else is just a noise.
 

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