Question

Radical hydroxyl OH is present only in a trace amount in the troposphere, although it plays a central role in photochemistry because it is a strong oxidizing agent. The reaction that yields the hydroxyl radical is i) O₃ → O* + O₂(the ozone is absorbing a minimum energy < 320 nm). ii) O* → O + hv, iii) O + H₂O  → 2 OH.

a)- In which wave range does the 320. nm belong to? Radio? Micro? Infra Red? Visible? UV? X-rays? Gamma?

b)- Calculate the minimum energy corresponding to 320 nm. (E = hc/λ), h = 6.63 x 10^-34 Js; c = 3.00 x 10⁸ m/s; 1 nm = 10^-9 m

c)- Why the concentration of OH is so small even though O₃ and H₂O are found in large quantity in the troposphere?

d)- The reaction between OH and SO₂ contributes to the formation of neutral HSO₃. Its next reaction is with O₂, forming sulfur trioxide and hydroxyperoxyl radical, followed by a fast reaction with H₂O, the rain.  Write out balanced equations (with all physical states), of this series of cascade reactions.

e) What is the approximate pH of a regular rain and of an acid rain?

Answer 1

e) Normal rainwater has a pH of 5.6 (slightly acidic). This is because it is exposed to the carbon dioxide in the atmosphere. Normal, clean rain has a pH value of between 5.0 and 5.5

which is slightly acidic

when rain combines with sulfur dioxide or nitrogen oxides—produced from power plants and automobiles the rain becomes much more acidic.

acid rain has a pH valueof 4.0.

a) UVB is generally defined as the wavelength range from 290-320nm

U.V -A=315-400nm (tanning rays)

UV.B(280-320) (BURNING RAYS)

b) E=hc/  

h = 6.63 x 10-34 Js; c = 3.00 x 108 m/s; 1 nm = 10-9 m

6.63x10^-34x3x108m/s/320x10^-9