Question

How many molecules of benzene $\left( C _{6} H _{6}\right)$ are there in $1\, L$ of benzene? Specific gravity of benzene is $0.88 .$ Express your answer in terms of $10^{24}$ molecules to the nearest possible integer.

Answer 1

$M_{w}$ of benzene $\left(C_{6} H_{6}\right)=12 \times 6+1 \times 6=78\, g$

1 litre of benzene $=1000 \,mL$

Mass of $1000 \,mL$ of benzene $=$ volume $\times$ density

$=1000 \times 0.88=880 \,g$

$\therefore 78 \,g$ of benzene $=6.023 \times 10^{23}$ molecules

$880\,g$ of benzene$ =\frac{6.023 \times 10^{23} \times 880}{78}$

$=6.795 \times 10^{24}$ molecules. $\Rightarrow 7$