Question

A mole of atoms is 6.02 x 10^23 atoms. To the nearest order of magnitude, how many moles of atoms are in a 8 kg domestic cat? The masses of a hydrogen atom, an oxygen atom, and a carbon atom are 1.0 u, 16 u, and 12 u, respectively. (Hint: Cats are sometimes known to kill a mole.)

Answer 1

The major problem with this question is that it doesn't tell you some important facts... Like 1 mole of carbon weights exactly 12g (this is the definition of a mole) and that, accordingly, 1 mole of hydrogen weights 1g.

Let's say a cat weights 5kg. (Just a guess.)

And now let's consider that a cat is about 60% water. The rest is mostly carbon and hydrogen.

So, 3kg of a cat is H20. Atomic mass of H20 is 18 (2 + 16).

So, 3000g of H20 contains x moles of H20. x = 3000/18 = 167 moles (approx). However, this is 167 moles of H20, which contains 3 atoms. So, 3000g of H20 actually contains 500 moles of atoms!

As another approximation, I'm gonna estimate that the remaining 2kg is made up of carbon and hydrogen in the ratio 2:1. Adding the atomic masses, C+H+H = 18. 2000/18 = 111 (approx). Since this calculation was once again empircal, I need to multiply by three to work out the number of atoms... 333 moles of atoms.

So, 500 + 333 = 833 moles of atoms. Or 1000 moles approx.

So, to the nearest order of magnitude, I would say a cat contains 1000 moles of atoms.