Respuesta :
Step 1 - Understanding molar mass
As we have previously seen, one mole corresponds to 6*10^23 particles.
When we weight one mole of something, we obtain what is called the molar mass: the mass of one mole of particles.
Each element has his own molar mass, which can be found in the periodic table. We can use them to calculate the molar mass of a molecule.
Let's see an example. Water is H2O. Looking at a periodic table, we find the molar masses 1 g/mol for H and 16 g/mol for O. Therefore, the molar mass of water will be:
[tex]M_{H2O}\rightarrow2H+1O=2\times1+1\times16=18\text{ g/mol}[/tex]Which means that 1 mole of water weights 18g.
Step 2 - Solving the exercise
Let's start by calculating the molar mass of C3H8. The molar mass for C is 12 g/molj, so:
[tex]M_{C3H8}=3C+8H=3\times12+8\times1=44\text{ g/mol}[/tex]44g corresponds thus to one mol of C3H8. Since one mole is 6.10^23 particles, we can set the following proportion:
[tex]\begin{gathered} 6.10^{23^\text{ }}particles\text{ of C3H8 ------ 44g} \\ 2.7\times10^{24}\text{ particles of C3H8 ----- x} \\ \\ x=\frac{2.7\times10^{24}\times44}{6.10^{23}}=\frac{1188}{6}=198g \\ \end{gathered}[/tex]Answer: 198g of C3H8 are present.
