# Chemistry qWatch

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#1
I understand part a but not b

Part a) a sample of an Unknown substance contains 1.204*10 to the power of 23 atoms.
How many moles of atoms of the element are there in the sample?
20 miles was what I got

B) given that the atoms have a mean mass of 9.3*10 to the power of -23 grams
What is the element? It would be great if you guys could explain part b to me! Thank you
0
1 week ago
#2
(Original post by ArtmisKco)
I understand part a but not b

Part a) a sample of an Unknown substance contains 1.204*10 to the power of 23 atoms.
How many moles of atoms of the element are there in the sample?
20 miles was what I got

B) given that the atoms have a mean mass of 9.3*10 to the power of -23 grams
What is the element? It would be great if you guys could explain part b to me! Thank you
part a you used avagadros constant...

part b you use molar mass= mass/moles

and then check the periodic table and match the element...
1
#3
Thank you very much! I was just wondering though so is the 9.3*10 to the minus 23 the molar mass and then you have to multiply it by Avogadro constant to get your mass which is the Ar?
Last edited by ArtmisKco; 1 week ago
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#4
I’m not sure I understand
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1 week ago
#5
(Original post by ArtmisKco)
Thank you very much! I was just wondering though so is the 9.3*10 to the minus 23 the molar mass and then you have to multiply it by Avogadro constant to get your mass which is the Ar?
no... you multiply by the avagadro constant to get question a...

for question b you use it and do moles divides by mass to get Ar and then find the element...
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#6
But my answer book says something different.
For part a you do 1.204*10 to the power of 25 (not 23 my mistake) and divide it by a Avogadros constant to get 20 moles
But for part b you do avogadros constant times by 9.3*10 to the power of -23 to get 56 so it is iron but I don’t understand part b
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#7

See it’s question 8a and 8b
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#8
I don’t think part b has an applied formula which is getting me confused
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1 week ago
#9
(Original post by ArtmisKco)
I understand part a but not b

Part a) a sample of an Unknown substance contains 1.204*10 to the power of 23 atoms.
How many moles of atoms of the element are there in the sample?
20 miles was what I got

B) given that the atoms have a mean mass of 9.3*10 to the power of -23 grams
What is the element? It would be great if you guys could explain part b to me! Thank you
a)
1 mol contains 6.02 x 1023 atoms

So your sample contains 1.204/6.02 = 0.2 moles of atoms

b)
if the average mass of 1 atom is 9.3 x 10-23g

Then 1 mol of these atoms have a mass of 9.3 x 10-23 x 6.02 x 1023 = 56g

The element is iron.
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