How many carbon atoms are in this sample?

Question

Consider a sample of 10.0 g of the gaseous hydrocarbon C2H6 to answer the following question: How many carbon atoms are present in this 10.0 g sample?

how many significant figures are there?

Answer 1

Recall Avogadro's number of 6.02x10²³ atoms/mole.

Let us first find the number of moles of C present in the sample.

moles of C₂H₆ = 10.0 g C₂H₆ x 1 mole C₂H₆ / 30.07 g = 0.33256 moles C₂H₆

Since there are 2 moles of C in each mole of C₂H₆, we can find the moles of C in the sample:

moles of C = 0.33256 moles C₂H₆ x 2 moles C/mol C₂H₆ = 0.66511 moles C

Using Avogadro's number, we can now find the number of C atoms in the sample:

0.66511 moles C x 6.02x10²³ atoms/mole = 4.00x10²³ C atoms (to 3 significant figures based on 10.0 g)