Question

Electromagnetic radiation of wavelength 242 nm is just sufficient to ionise the sodium atom. Calculate the ionisation of sodium kn kJ mol${}^{-1}$:

• A. 8.8266 $\times$ 10${}^{-35}$ m
• B. 8.8266 $\times$ 10${}^{35}$ m
• C. 8.8266 $\times$ 10${}^{-36}$ m
• D. 8.8266 $\times$ 10${}^{-34}$ m

Answer 1

Answer: (A)

8.8266 $\times$ 10${}^{-35}$ m

The ionization energy of sodium will be equal to the energy possessed by the radiation of wavelength 242 nm. It is

E = $\frac{hc}{\lambda }$ =$\frac{6.62\times {10}^{-34}Js\times {10}^{8}m{s}^{-1}}{150\times {10}^{-3}kg\times 50m{s}^{-1}}$= 8.8266 $\times$ 10${}^{-35}$ m