Answer to Question #114283 in General Chemistry for Daniel

Question

How many grams of carbon are there in 4.35x1025 molecules of C2H6?

Answer 1

We know that the mass of carbon $m$ can be calculated from its number of the moles $n$:

$m(C) = n·M$ ,

where $M$ is the molecular weight of carbon: 12.01 g/mol.

The number of the moles of carbon and the number of the moles of C₂H₆ relate as:

$n(C) = 2·n(C_2H_6)$ ,

because there are two atoms of carbon in each C₂H₆ molecule.

The number of the moles of C₂H₆ can be calculated from the number of the molecules, using the Avogadro constant ($N_A$ , 6.022·10²³ mol^-1):

$n(C_2H_6) = N/N_A = 4.35·10^{25}/6.022/10^{23} = 0.722·10^{2} = 72.2$ mol.

Finally, the mass of carbon:

$m(C) = 2·72.2·12.01 = 1735$ g.

Answer: There is 1735 g of carbon in 4.35·10²⁵ molecules of C₂H₆.