Question

the atomic mass for boron is 10.811 g. how many molecules are in 320 g?

Explanation:

Step1: Find moles of boron

Moles ($n$) = $\frac{\text{mass (g)}}{\text{molar mass (g/mol)}}$. Molar mass of B is 10.811 g/mol, mass is 320 g.
$n = \frac{320\ \text{g}}{10.811\ \text{g/mol}} \approx 29.6\ \text{mol}$

Step2: Find number of molecules

Use Avogadro's number ($N_A = 6.022 \times 10^{23}\ \text{molecules/mol}$).
Number of molecules ($N$) = $n \times N_A$
$N = 29.6\ \text{mol} \times 6.022 \times 10^{23}\ \text{molecules/mol} \approx 1.78 \times 10^{25}\ \text{molecules}$

Answer:

Approximately $1.78 \times 10^{25}$ molecules