When gold crystallizes, it forms face-centred cubic cell. The unit cell edge length is 408 pm. Calculate the density of gold. [ Molar mass of gold = 197 g. mole–1 ] Which flower is an example of self cleaning? Write the monomer used for preparation o…

Answer: Density of gold ≈ 19.27 g cm⁻³; lotus; vinyl chloride

For fcc, \(n = 4\) atoms per unit cell; \(a = 408\) pm \(= 408\times10^{-10}\) cm \(= 4.08\times10^{-8}\) cm.

\(a^3 = (4.08\times10^{-8})^3 = 67.92\times10^{-24}\) cm³ \(= 6.792\times10^{-23}\) cm³

\(\rho = \dfrac{nM}{a^3 N_A} = \dfrac{4\times197}{6.792\times10^{-23}\times6.022\times10^{23}} = \dfrac{788}{40.90} = 19.27\) g cm⁻³

Self-cleaning flower: the lotus (its leaves and petals are superhydrophobic because of nanostructures on the surface, so water droplets roll off carrying dirt; the ‘lotus effect’).

Monomer of PVC: vinyl chloride (chloroethene), CH₂=CHCl.