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Environmental Chemistry — Chemistry STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceChemistryEnvironmental Chemistry3 Marks
Question
Explain the following terms:
  1. Photochemical smog.
  2. Acid rain.
  3. Eutrophication.
✓

Answer

  1. Photochemical Smog: It is due to the formation of free radicals. They are formed when sunlight is absorbed by $\text{SO}_2$ oxides of nitrogen and hydrocarbons. They are oxidising agents.
  2. Acid Rain: Acid rain is caused by the presence of oxides of sulphur and nitrogen and $\text{CO}_2$, in the atmosphere. When pH of the rain drops below 5.6, it becomes acidic.
$\text{H}_2\text{O(l)}+\text{CO(g)}\xrightarrow{\ \ \ \ \ \ }2\text{H}^+(\text{aq})+\text{CO}_3^{2-}\text{(aq)}$
$2\text{SO}_2(\text{g})+\text{O}_2\text{(g)}+2\text{H}_2\text{O(l)}\xrightarrow{\ \ \ \ \ \ \ }2\text{H}_2\text{SO}_4(\text{aq})$
$4\text{NO}_2(\text{g})+\text{O}_2(\text{g})+2\text{H}_2\text{O(l)}\xrightarrow{\ \ \ \ \ \ \ \ }4\text{HNO}_3(\text{aq})$
The source of $\text{CO}_2$, and $\text{SO}_2$, is burning of fossil fuels, ore smelting, petroleum refining and sulphurbased industries.
Nitrogen oxides are emitted into the atmosphere mainly from automobile exhausts and fossil fuel combustion.
  1. Eutrophication: Water bodies receives large quantities of nutrients like nitrates and phosphates which helps in production of algae population. This leads to eutrophication.

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