Question 1028603
i'm not quite sure what you're asking here.


you state that 1 mole of carbon 12 has a mass of 12 grams and contains 6.022 * 10^23 atoms of carbon 12.


this means that 6.022 * 10^23 atoms of carbon 12 has a mass of 12 grams.


you can solve the the mass of one carbon 12 atom by dividing 12 by 6.022 * 10^23.


since 12 is equivalent to 12 * 10^0, you would then divide 12 * 10^0 by 6.022 * 10^23 which will result in 12/6.022 * 10^0/10^23 which will then be equal to 1.992693457 * 10^-23 grams.


that should answer your first question which was:


what is the mass of 1 carbon 12 atom.


the solution is that one carbon 12 atom has a mass of 1.992693457 * 10^-23 grams.


your second question was:


What is the mass of carbon-12 atoms in 20.0g of carbon-12?


the solution to that should be 20 grams.


you might have asked how many atoms of carbon 12 in 20 grams of carbon 12.


that would then be 20/12 * 6.022 * 10^23 = 10.03666667 * 10^23 atoms.


if you multiply that by the mass per gram of carbon 12, you should get 20.


i did and i got 20 grams, as i should have.


your last question asks how many moles are in 20 grams of carbon 12.


if 1 mole weights 12 grams, then take 20 and divide it by 12 and you will get 20/12 = 1.6666666666.... moles, which is equal to 1 and 2/3 moles.


i think this is right.
check it out and get back to me if you don't agree, or if the solutions that you're supposed to get don't agree.