Find Number of Neutrons in a Copper Bar given volume of bar?

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Discussion Overview

The discussion revolves around calculating the number of neutrons in a copper bar, given its dimensions and density. Participants explore the implications of copper's isotopes and how to incorporate this information into their calculations.

Discussion Character

  • Homework-related
  • Mathematical reasoning

Main Points Raised

  • One participant presents a calculation for the number of neutrons based on the volume and density of copper, expressing uncertainty about the use of isotopic information.
  • Another participant clarifies that the average atomic mass of copper (63.546 g) already incorporates the isotopic abundances, suggesting that the isotope information may not be necessary for the initial calculation.
  • A further response indicates that the isotopic contributions should be explicitly calculated to refine the average used in the calculations, proposing a weighted average based on the isotopic abundances.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether the isotopic information is necessary for the calculations, with differing views on its relevance to the problem.

Contextual Notes

There is a lack of clarity regarding the assumptions made in the calculations, particularly concerning the treatment of isotopes and the use of average atomic mass.

viper2308
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Homework Statement

A bar of copper has dimensions 0.5605 ft. x 3.545 in x 5.722 cm. The density of copper is 8.921 g / cm3. Copper contains 2 isotopes, 63Cu (69.09% abundant) and 65Cu (30.91% abundant). How many neutrons are in the bar of copper?

The attempt at a solution

I took the volume: 11.37cm^3 x 8.921g/cm^3 x 6.022E23 neutrons/63.546g Cu = 9.612E23 neutrons.

Is this right? I think I need to use the isotope information somewhere but I don't know where or how.
 
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You have already used the isotope information, 63.546g is the weighted average of the two isotopes
 
Ok I just got the from the periodic table. So the isotope information is unnecessary?
 
>63Cu (69.09% abundant) and 65Cu (30.91% abundant)
Means that a sample = 63 * 69.09/100 + 65 * 30.91/100 = 63.618
You should probably use this value in your calcs.
 

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