Question

How many atoms are there in a 36.5 g sample of ${SF}_6$ gas?

• A. $1.51\times {10}^{22}$
• B. $1.06\times {10}^{22}$
• C. $1.51\times {10}^{23}$
• D. $1.06\times {10}^{24}$
• E. $1.51\times {10}^{-24}$

Answer 1

Answer: (D)

$1.06\times {10}^{24}$

Molar mass of $S{F}_6=32+19\times 6=146g/mol$

Moles of $S{F}_6$ in $36.5g=\frac{36.5}{146}=0.25$

In 1 mol of $S{F}_6$, there are 7 atoms.

Hence, in 0.25 moles of $S{F}_6$ there are $0.25\times 7=1.75$ mole atoms.

1.75 moles of atoms $=1.75\times 6.022\times {10}^{23}=1.06\times {10}^{24}$ atoms.