How Do You Calculate Molar Mass from BCC Packing?

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Discussion Overview

The discussion revolves around calculating the molar mass of an element with body-centered cubic (bcc) packing, given its density and unit cell volume. The focus is on the application of relevant equations and unit conversions in the context of a homework problem.

Discussion Character

  • Homework-related

Main Points Raised

  • One participant states the known values: density (862 kg/m³) and unit cell volume (1.51 x 10⁻²⁸ m³), and seeks to calculate the molar mass.
  • The same participant attempts a calculation but expresses uncertainty about arriving at the correct answer, mentioning a result of 26.6504 and referencing a packing density of 0.68.
  • Another participant questions the relevance of the packing density to the problem.
  • A subsequent reply acknowledges that the packing density was not required for the calculation.
  • Another participant asks if the first poster understands their approach and reasoning.
  • The first poster responds affirmatively, indicating they converted units correctly but struggled with achieving the correct units for the final answer.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the necessity of the packing density in the calculation, and there is uncertainty regarding the correctness of the initial calculation approach.

Contextual Notes

Participants express uncertainty about the relevance of packing density and the proper handling of units in the calculation process. There are unresolved aspects regarding the calculation steps leading to the molar mass.

vipertongn
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Homework Statement



An element has bcc packing with a body-centered cubic unit cell. Its density is 862 kg/m^3 and the unit cell volume is 1.51 x 10-28 m^3. Calculate the molar mass (g/mol) of the element to three significant figures.

Homework Equations



Known: D= 862 kg/m^3, V=1.51 x 10-28 m^3 , MM=??

The Attempt at a Solution



Ok the correct answer is 39.2, but I don't know how to arrive to that answer.

(862kg/m^3)(1.51e-28m^3)(1000g/1kg)(6.022e23atoms/1mol)(1/2 atoms)
(0.68) but instead I get 26.6504.

The 0.68 is the density packing.
 
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vipertongn said:
The 0.68 is the density packing.

Are you sure it is relevant to the question?
 
ah, htat wasn't required, thanks
 
The real question is: do you understand what you did and why?
 
Yes, I pretty much converted to the proper units I needed, the only problem was getting the right units.
 

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