mommyto3girls wrote:I need to find the mass of the element Neodymium that is 1000. cubic centimeters. I am not sure how to do this can anyone elp? PLEASE!!!!!! I also need to figure out the # of atoms and the # of mole if anyone can help there. Thanks
As Shill pointed out, the density of Neodymiun is 6,800 Kg/mÂ³, however, to convert Kg/mÂ³ to g/cmÂ³, the process is:
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6,800 Kg x 1,000 g/Kg = 6,800,000 g
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1 mÂ³ x 1,000,000 cmÂ³/mÂ³ = 1,000,000 cmÂ³
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6,800,000 g
------------- = 6.8 g/cmÂ³
1,000,000 cmÂ³
We have 1000 cmÂ³, so 6.8 g/cmÂ³ x 1000 cmÂ³ = 68,000 g or 68 Kilograms.
The answers to the last two questions are closely tied together. They hinge on the value of the mole. the mole is one of the seven basic definitions of the SI system, and is defined as: "The mole is the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon-12."
Now, The number of atoms in 0.012 kg of carbon-12 is 6.0221367 x 10Â²Â³ - This number was named "Avogadro's number" in honor of Amedeo Avogadro, who's work lead to the definitition of this value.
Now, science mumbo-jumbo aside, this means that a mole is the quantity of a substance whose weight in grams in equal to the molecular weight of the substance. In other words, a mole of one thing has Avogadro's number of that thing in it. A mole of flowers is 6.0221367 x 10Â²Â³ flowers. Not a good unit for measuring large things, but a great unit for measuring tiny things - Like so:
The weight of your 1,000 cmÂ³ block of Neodymium is 68,000 grams.
In order to find the number of moles, we need to know the atomic weight of neodymium. We can look that up in just about any periodic chart, and get a value of 144.24 grams.
Now, since a mole is the quantity of a substance whose weight in grams in equal to the molecular weight of the substance, then we need to divide the number of grams we have, by the molecular weight, in grams, and we'll find out how many moles we have:
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68,000 g
------------- = 471.43 mol
144.24 g/mol
There. You've got 471.43 moles of Neodymium.
Next, since we know that one mole is equal to Avogrado's number of molecules:
471.43 mol x 6.022x10Â²Â³ atoms/mol = 7.829x10^26.
471.43 moles means that You've got 782,300,000,000,000,000,000,000,000 atoms. As you can see, it's much easier to say that that you've got 471.43 moles of Neodymium.
William J. Knight
Health Physicist
Los Alamos National Labs