Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: jennielynn_1980 on May 17, 2006, 10:02:16 PM
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I am trying to find the number of atoms in the following
a) 52.5 g calcium metal
b) 1.5 mol carbon
c) 1.5 mol carbon dioxide
So I have to find the molar mass for each before proceding right? In which case the molar mass for
a) is 40.078 g/mol
b) 12.0107 g/mol
c) How do I find the molar mass for this? Is it the molar mass for carbon plus the molar mass for oxygen multiplied by 2?
Thanks :)
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Yes
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then use avagodro's (hope i spelled that right) number to convert moles to atoms
in other words, multiply number of moles by 6.02x1023
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avagodro's (hope i spelled that right)
Nope ;)
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avagodro's (hope i spelled that right)
Nope ;)
Avogadro's... that's a little better
and if you want to be more precise, Avogadro's number = 6.0221415 × 1023
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So for
a) the answer would be 0.7394
b) 1.9999
c) 1.4999
Is this right? Or am I missing a step?
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aren't the units atoms/mol??
if that's correct then your answers would be wrong
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for the first i got 7.89E23
second and third it should be 9.033E23
because you take moles*avogadro's number to get atoms and the second and third are already in moles so they need no change.
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for the first i got 7.89E23
second and third it should be 9.033E23
because you take moles*avogadro's number to get atoms and the second and third are already in moles so they need no change.
b and c wouldn't be the same because one molecule contains a different number of atoms. b is probably double your answer because pure carbon typically bonds with itself to form C2. C is probably triple your answer because there are 3 atoms (1 carbon and 2 oxygen) in one molecule of carbon dioxide. I say probably on these because i didn't actually calculate, i'm just assuming you took 1.5*6.02*10^23.
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A i got, 4.7E23
40g/mol / 52.5g x 6.2E23atoms/mol leaves 4.7E23atoms
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tennis freak is right for A & B and syko sykes got C right.
A is: (52.5 / 40.078) x (6.0221415 × 1023) which is 7.889 x 1023 atoms.
For B and C you don't need to worry about Mr of carbon etc. because it already tells you the moles. For B it fair to assume that they mean carbon atoms because there are so many allotropes of carbon (graphite (and diamond to some extent) being the most common), you don't know which one they are talking about. It is also possible to make carbon atoms but it is extremely difficult and dangerous.
Hence,
B is: 1.5 x (6.0221415 × 1023) which is 9.033 x 1023 atoms.
For C you multiply this by 3 because there are 3 atoms in a CO2 molecule.
C is: 3 x 1.5 x (6.0221415 × 1023) which is 2.71 x 1024 atoms.
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Thank you all! I was confused with the wording of it all. I have never taken chemistry before and I am enrolled in advanced 12th grade chem :-\ so my head is spinning a bit as it is also a home study course.
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believe me this website would have helped me so much more if i had found it sooner, so just keep asking questions on here and you should be fine :)
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I already love this site! Everyone here is very helpful and friendly :)
One last question about this:
if one mole = 6.02 x 1023 of any substance, then why do I multiply 1.5 moles of CO2 by three? Should the answer not be the same as the second seeing as the moles are the same? I can see that there are two oxygens and one carbon but if it is still 1.5 moles then shouldn't the number of particles be the same?
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if one mole = 6.02 x 1023 of any substance, then why do I multiply 1.5 moles of CO2 by three? Should the answer not be the same as the second seeing as the moles are the same? I can see that there are two oxygens and one carbon but if it is still 1.5 moles then shouldn't the number of particles be the same?
You understand the chemistry perfectly- there are the same number of particles in B as C, but the question is asking about the number of atoms (I think!), and there are 3 atoms in one CO2 particle, so you multiply it by three. If the question asked for the number of particles then B would be the same as C.
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okay so if the question had been the number of atoms in Cl2 then I would have muliplied 1.5 by two right?
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okay so if the question had been the number of atoms in Cl2 then I would have multiplied 1.5 by two right?
Absolutely correct! ;)
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I used to think of mole as similar to the term dozen.
For example:
If you had a bowl with two apples in it apple2 and you had 1 dozen bowls you would have 24 apples, right?
1 dozen (12) apple2 = 24 apples
1 mole (6.02 x 1023) Cl2 = 12.04 x 1023 Cl atoms
hmmm, now that I write this I am not sure if anyone will understand, let me know if this is a good analogy or not ;)
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That's a good analogy! Thanks for sharing :)