What Is the Formula of a Mixed Copper Salt Formed with OH- and Br- Ions?

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Discussion Overview

The discussion revolves around determining the formula of a mixed copper salt formed from Cu2+, OH-, and Br- ions. Participants explore the calculation of moles of Cu2+ and OH- in the context of a chemistry homework problem, addressing the stoichiometry involved in the reaction and the implications of hydration in the compound.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant calculates the moles of OH- based on the volume and molarity of NaOH, arriving at 0.00567 moles.
  • Another participant questions the inclusion of 2H2O in the calculation of moles of CuBr2, seeking clarification on its relevance.
  • There is a discussion about the analogy of counting bicycles and tires to explain the relationship between moles of CuBr2 and moles of Cu, with some participants expressing confusion over the analogy.
  • One participant asserts that CuBr2 is hydrated, while another challenges this assertion based on the molar mass provided, suggesting that the problem does not indicate hydration.
  • Clarification is sought regarding the stoichiometry of CuBr2 and the number of Cu atoms present in relation to the number of CuBr2 molecules.

Areas of Agreement / Disagreement

Participants express differing views on whether CuBr2 is hydrated, leading to a lack of consensus on this point. Additionally, there is uncertainty regarding the correct interpretation of the stoichiometric relationships in the problem.

Contextual Notes

The discussion includes assumptions about the hydration state of CuBr2 and the implications of using molar mass in calculations, which remain unresolved. The analogy used to explain mole relationships may not effectively convey the intended concept.

wcbryant87
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Homework Statement



Cu2+OH-, and Br- form a mixed salt formula Cux(OH)yBrz. In an experiment to determine the values of x, y, and z in the formula of this compound, .760 g CuBr2 (223.4 g/mol) was dissolved in water and reacted with 10.22 ml 0.555M NaOH. Assume that in this reaction, all of the Cu2+ from the CuBr2 and all of the OH- from the NaOH were incorporated into the product but that not all of the Br- was used.

Calculate the number of moles of Cu2+ and OH- in the product.



Homework Equations





The Attempt at a Solution


10.22mL * 1/1000L * .555M NaOH = .00567 mols OH-
I think that is right...but it's finding the moles of Cu that is stumping me.

.760g CuBr2 * 2H2O * 1/259.4 = .00293 mol CuBr2

Now I don't know how to get from that to mols of just Cu. I don't have a volume or anything.
 
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.760g CuBr2 * 2H2O * 1/259.4 = .00293 mol CuBr2

2H2O? Two water molecules? Where did they come from?

I don't know how to get from that to mols of just Cu.

If you have a dozen bicycles, how many tires do you have? Two dozen, right?
If you have a dozen molecules of CuBr2, how many atoms of Cu do you have? Two dozen.

A mol is just a quantity. Like dozens.

So if you have a mol of CuBr2 molecules, how many moles of Cu do you have?
 
alxm said:
2H2O? Two water molecules? Where did they come from?



If you have a dozen bicycles, how many tires do you have? Two dozen, right?
If you have a dozen molecules of CuBr2, how many atoms of Cu do you have? Two dozen.

A mol is just a quantity. Like dozens.

So if you have a mol of CuBr2 molecules, how many moles of Cu do you have?

The 2H2O is because it's a hydrate.

You kind of lost me on the dozen analogy though. If you have a dozen CuBr2 molecules wouldn't that just be a dozen Cu atoms?
 
wcbryant87 said:
If you have a dozen CuBr2 molecules wouldn't that just be a dozen Cu atoms?

Yes, that's probably what alxm meant.

Why do you think CuBr2 is hydrated? Judging from the molar mass given it is not.
 
wcbryant87 said:
The 2H2O is because it's a hydrate.

Do you know that? Typically these problems would include that information if it was needed, e.g. by writing CuBr2*2H2O.

You kind of lost me on the dozen analogy though. If you have a dozen CuBr2ical molecules wouldn't that just be a dozen Cu atoms?

Whoops, my mind must've slipped. Yes, a dozen Cu and two dozen Br.
(Typical.. screwing up a perfectly simple analogy)
 

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