HELP! I have a variety of materials and I have to measure the mass, and calculate the number of mole, the number of individual units (molecules/compounds), and the number of atoms for a variety of samples.

Question

anonymous · Answer

I already have the mass of four materials:

Chalk (CaCO3): 2.04 g, 
Water (H2O): 32.0 g,
Iron (fe): 15.87 g
Copper (Cu): 0.59 g

I know how to find the molar mass (calculate the number of moles?) but I don't know how to calculate the number of individual units (molecules/compounds), and the number of atoms for a variety of samples.. Please help!!

jfraser · Answer

1 mole of anything is 6.022x10^23 humber of those things. 1 mole of calcium carbonate will have that many molecules of that substance. This means you can use the equality as a conversion factor:
$$2.04g CaCO{_3} * (\frac{1mol CaCO{_3}}{100g CaCO{_3}})*(\frac{6.02x10{^2}{^3}molecules CaCO{_3}}{1mol CaCO{_3}}) $$

anonymous · Answer

Is number of entities (basically what you showed me where n=NA) the "number of individual units"?

How do I find the number of atoms for a variety of samples? A teacher told me that I should just count how many atoms there are in a compound.. like say Al3O2, which means there are 3 Aluminum, and 2 oxygen or 5 in total.

jfraser · Answer

A single molecular unit of something like Al2O3 has 5 atoms total, correct. 1 MOLE of Al2O3 will have 6.022x10^23 molecules, and also 2 moles of Al atoms and 3 moles of O atoms, for 5 MOLES  of atoms total. A mole is a term of grouping, just like a dozen. If you had 1 dozen eggs, you'd have just as many THINGS as if you had 1 dozen elephants. The MASSES of those things would be very different, but the number of items would be the same.