How do I find out how many atoms of chalk it takes to write my name?

Question

(lab)

I weighed the chalk on an electronic scale, wrote my name on the board then reweighed the chalk. It decreased from 9.27g to 9.25g. Now I have to convert it to molecules so I divided it by CaCO3's atomic mass (100.09g) and multiplied it by 6.02x10^23 and got 5.57x10^23 particles. Is this right?

Answer 1

actually no.
if you want to find how many atoms of chalk it takes to WRITE your name, then you need to USE the weight of the the chalk it took to write your name.
so 9.27g - 9.25g = .02g of chalk it took to write your name.
then do .02 / 100.09 × 6.02x10^23 = 1.2029 × 10^20 atoms of chalk.

Answer 2

The approach is correct, although there is a mathematical error somewhere. There is a problem with nomenclature -- you (correctly) did calcium carbonate's molecular (not atomic) mass. As for the mathematical details, you used 20 milligrams of chalk, which is 0.2 millimoles, which times 6E23 gives 1.2E20 molecules of calcium carbonate. Each such molecule has five atoms, so we wind up with 6E20 atoms altogether.

Answer 3

Were you using real chalk or commercial blackboard "chalk". The latter is not calcium carbonate but gypsum or calcium sulfate (CaSO4) mixed with binders.

BTW you are using the terms atoms and atomic weight where you should be using molecules and molecular weight.

Answer 4

Hi. Depends on what your name is and how small you write it. Could be just a few molecules.

Answer 5

absolutely fine