# Chemistry

Copper is composed of two naturally occurring isotopes: Cu−63 (69.170%) and Cu−65. The ratio of the masses of the two isotopes is 1.0318.

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1. What is the mass of Cu−63?

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posted by Vanessa
2. I believe you also need to know the mass of the mixture occurring in nature.

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posted by DrBob222
3. I just asks me to figure out the mass of Cu-63? the mass of nature is 69.170% for Cu-63 and for Cu_65 it is 30.83%

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posted by Vanessa
4. I don't think you understand what I need. The ABUNDANCE of 63 is 69.170% and the ABUNDANCE of 65 is 30.83%. But you don't have the mass of anything; i.e., you don't have the mass of 63 or the mass of 65 or the mass of the isotope as it occurs in nature (the mixture). Here is as far as I can go.
Let x = mass Cu63
and y = mass Cu65
and z = mass of naturally occurring isotope.
--------------------
x(0.69170)+(y)(0.3083) = z
Three unknowns and you can't solve the equation. You can relate x and y with the ratio data. You don't say which ratio is which but I presume that is mass Cu65/mass Cu63 = 1.0318 and that lets us write
y/x = 1.0318 or y = 1.0318x and that can be substituted into the above for
x(0.69170) + (1.0318x)(0.3083)= z.
I believe you need another piece of information, namely z, to solve the equation.

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posted by DrBob222
5. would is be the atomic number for the element Cu?

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posted by Vanessa
6. That is all the information they gave me that is why I ask

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posted by Vanessa
7. No it isn't the atomic number; however, I looked up the atomic mass on the periodic table and it is 63.5463 as it occurs in nature. Plug that in for z and solve.

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posted by DrBob222
8. I got 16.99?

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posted by Vanessa
9. never mind its not that

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posted by Vanessa
10. I have this same problem and have trying to figure it out forever, I have no idea how to solve this.

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posted by Griffin
11. The response written by DrBob is correct. Using a substitution method with the y=1.0318x, substitute the y in the original formula for 1.0318x, and solve. Keep in mind that you must set z=63.5463 (or just 63.55), otherwise you cannot hope to solve for the abundance of Cu-63.

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posted by Cristian
12. what

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posted by ll
13. x*0.69170+x*1.0318*(1-0.69170)=63.546

If you don't understand
joonchun1000@gmail.com

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