- The standard used by scientists to compare unites of atomic mass is the carbon-12 atom, which has been arbitrarily assigned a mass of exactly 12 atomic mass units, or 12 amu.
- One atomic mass unit, or 1 amu, is exactly 1/12 the mass of a carbon-12 atom.
- The atomic mass of any atom is determined by comparing it with the mass of the carbon-12 atom.
Average Atomic Masses of Elements
- Average Atomic Mass is weighted average of the atomic masses of the naturally occurring isotopes of an element.
Calculated Average
- The average atomic mass of an element depends on both the mass and the relative abundance of each of the element's isotopes.
Copper consists of 69.15% copper-63, which has an atomic mass for 62.929601 amu, and 30.85% copper-65, which has an atomic mass of 64.9227794 amu.
The average atomic mass of copper can be calculated by multiplying the atomic mass of each isotope by its relative (abundance expressed in decimal form) and adding the results.
You must learn how to do this because it will be a test question.
(0.6915)*(62.929601)=43.5158909
(0.3085)*(64.927794)=20.03022445
43.5158909+20.03022445=63.54611535, which is rounded to 63.55 amu
Relative Mass to the Number of Atoms
The Mole
- The mole is the SI unit for the amount of substance.
- A mole(abbr. mol)is the amount of substance that contains as many particles as there are atoms in exactly 12g of carbon-12.
Avogardo's Number
- Avogardo's Number ~ 6.0221415*10^23 ~ is the number of particles in exactly 1 mole of a pure substance.
Molar Mass
- The mass of 2 mole of a pure substance is called the molar mass of that substance.
- Molar mass is usually written in units of g/mol.
- The molar mass of an element is numerically equal to the atomic mass of the element in atomic mass units.
Gram/Mole Conversions
- Chemist use molar mass as a conversion factor in chemical calculations.
- For example, the molar mass of helium is 4.00g the 1mol He.
- To find how many grams of helium there are in 2 moles of helium, multiply by the molar mass.
2.00 mol He * 4.00gHe/1 mol He = 8.00 g He
Conversions with Avogardo's Number Avogardo's Number can be used to find the number of atoms of an element from the amount in moles or to find the amount of an element in moles from the number of atoms.
- In these calculations, Avogardo's number is expressed in units of atoms per mole.
Amount of Element in moles*Molar Mass of Element/1 mol = Mass of Element in grams
Mass of Element in grams*1 mol/Molar Mass of Element= Amount of Element in moles
Mass of Elem. in grams*1 mol/Molar Mass of Elem.* 6.022 x 10^23 atoms/1 mol=Number of Atoms of Elem.
Number of Atoms of Elem.* 1 mol/6.022 x 10^23 atoms * Molar Mass of Elem.= Mass of Elem. in grams
Number of Atoms of Elem.* 1 mol/6.022 x 10^23 atoms = Amount of Elem. in Moles
Amount of Elem. in Moles* 6.022 x 10^23 atoms / 1 mol = Number of Atoms of Elem.
Example
- What's the mass in grams of 3.50 mol of the element Copper, CU?
(3.50 mol CU * 63.55 g CU)/ 1 mol CU = 222 g CU
This comment has been removed by the author.
ReplyDeleteThis website brings lots of different comparisons to explain how big a mole is...
ReplyDeleteP.S. It talks about Fruit Loops and trips to Pluto
http://www.ed.mtu.edu/esmis/id61.htm
This is great practice for calculating average atomic mass:
ReplyDeletehttp://www.algebralab.net/practice/practice.aspx?file=Algebra_AverageAtomicMass.xml
I found this site helpfull http://misterguch.brinkster.net/molecalculations.html
ReplyDeleteThis is a biography that tells you about Amedeo Avogadro's life and career
ReplyDeletehttp://www.corrosion-doctors.org/Biographies/AvogadroBio.htm
http://www.thenakedscientists.com/forum/index.php?topic=8046.0;prev_next=prev
ReplyDeleteThis site explains in a Q and A form, how to use the mole
for anyone who does not understand the concept of the mole, it is like a dozen of eggs or a dozen of bricks. while those two sets are very different, they do have the same amount of items. a mole is just an amount of an item.
ReplyDeleteA mole doesn't necessarily have to be a pure substance, it can be an amount of any item, such as cars or popcorn
ReplyDeletehttp://en.wikipedia.org/wiki/Avogadro_constant
ReplyDeleteThis site helps with Avogadro's number
In other words, 1 mol of Au has a different mass than 1 mol of C
ReplyDeletehttp://antoine.frostburg.edu/chem/senese/101/moles/index.shtml
ReplyDeletethis website is great for learning about the mole.
P.S. Nick, great post!
http://www.mindbites.com/lesson/4705-chemistry-conversions-of-masses-moles-particles
ReplyDeleteThe end of this video explains the purpose of having moles pretty clearly. There are also some links to videos on related subjects on this same page.
molar mass is the amount of mass in 1 mole, not 2
ReplyDeleteHere's another site explaining moles.
ReplyDeletehttp://web.utk.edu/~dad/mole.html
http://misterguch.brinkster.net/molecalculations.html This website explains calculations with moles very well
ReplyDeletehttp://www.fordhamprep.org/gcurran/sho/sho/lessons/lesson92.htm
ReplyDeleteThis site has sample problems for molar mass conversions.
http://www.grossmont.net/tomolmstead/general%20chemistry/conversions_uisng_avogadro.pdf
ReplyDeleteThis site explains moles and avagadro's number,
(REQUIRES and .PDF READER)
this gives you an idea of how big a mole is
ReplyDeletehttp://answers.yahoo.com/question/index?qid=20081019201117AAXZNsZ
This site goes into relative atomic mass and how it is calculated:
ReplyDeletehttp://www.avogadro.co.uk/definitions/ar.htm