Chemistry Assignment

Question

How many atoms of carbon are present in
12.9 g of a compound that is 36.7% carbon, by
weight?
Answer in units of atoms.

Multiplying the latter by the Avogadro's number, obtain 0.394 * 6.022 * 10^23 = 2.37 times 10^23 atoms of C.

 

How do I get the number of atoms?

 

Answer 1

First you want to find the mass of just the Carbon in the compound

12.9 g x 0.367 = 4.73 grams

Then convert that over to moles by dividing by the molar mass of Carbon

4.73 grams / 12.01 = 0.394 mol

Finally then you can multiply by Avogadro's number to convert that over into atoms

0.394 mol x (6.022 x 10^23 atoms/mol) = 2.37 x 10^23 atoms

meaning that the number of carbon atoms present in the compound is approximately 2.37 x 10^23 atoms

Answer 2

So, to begin, determine how much of your compound is carbon.

We know that it is 36.7% carbon by mass and the overall mass of the compound is 12.9g.

 

(12.9 g) * (.367) = 4.73 g of C in sample.

 

Now convert this mass to a number of moles of C.

 

(4.73 g C) * (1 mol C / 12.011 g C) = 0.394 mol C

 

Now to the number of atoms, using Avogadro's Number:

 

(0.394 mol C) * (6.022x10²³ atoms / mol) = 2.37x10²³ atoms of C

 

Your calculation gave you the number of atoms of carbon in the sample