principle of chemistry: intro

7/29/2019 Principle of chemistry: Intro

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PRINCIPLE OF CHEMISTRYENV 110

Chapter 1


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Environmental Link to Chemistry

Water

-Drinking water-Recreational water-Waste water

Food-Food spoilage

Built Environment-Disinfection, antiseptic, bleaching


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Effect of air pollution Acid rain


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Several processes can result in the formation of aciddeposition.

Nitrogen oxides (NOx) and sulfur dioxide (SO2) released

into the atmosphere from a variety of sources call fall to theEarths surface simply as dry deposition.

This dry deposition can then be converted into acids when.

Most wet acid deposition occurs when nitrogen oxides(NOx) and sulfur dioxide (SO2) are converted to nitric acid(HNO3) and sulfuric acid (H2SO4) through oxidation anddissolution in the atmosphere. Wet deposition can alsoform when ammonia gas (NH3) from natural andagricultural sources is converted into ammonium (NH4).


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Food spoilage

Chemical reactions such as oxidation also

contribute to food spoiling. Oxidation occursnaturally in all foods and causes a loss of nutritional value and chemical changes of thefoods ro erties.

Molecular oxygen combines with nutrients in thefood, creating rancidity. Oxidative rancidity occursin a three-step process:


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Disinfection

The process of killing pathogenic organisms or

rendering them inert.

Disinfectant: An agent, such as heat, radiation, or, ,

neutralizing, or inhibiting the growth of disease-carrying microorganisms.

- Chlorines, chloramines, chlorine dioxide,ozone.


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Chlorine is generally applied to the process wateras an aqueous chlorine solution: chlorine gas ishydrolyzed to form hypochlorous acid, HOCl, andhypochlorite ion (OCl-) in ammonia free water.

Hydrolysis: Cl2 + H2O HOCl + H+ + Cl-

Ionization: HOCl H+ + OCl-

Chlorine reacts with ammonia to formchlroamines which less effective disinfectants thanchlorine.

NH3 + HOCl NH2Cl (monochloramine) + H2ONH2Cl + HOCl NHCl2 (dichloramine) + H2O

NHCl2 + HOCl

NCl3 (nitrogen trichloride) + H2O


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Generation of chlorine dioxide involves reactingsodium chlorite (NaClO2) with chlorine to producegaseous chlorine dioxide as follows:

2NaClO2 + Cl2 2ClO2 + 2NaCl

Among commonly available disinfectants, ozone is

e mos power u ox an an s n ec an .

Produce ozone:

O2(high voltage) O + OO + O2 O3


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Ozone disinfection:

O3 + H2O HO3+ + OH-

HO3+

+ OH-

2HO2O3 + HO2 HO + HO + HO2 H2O + O2

,2

oxidizing powers.


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Bleaching

Bleaching Agents

Bleaching agents are compounds which are usedto remove color from substances such as textiles.

such as sodium hypochlorite (NaOCl) or hydrogenperoxide (H2O2) which are quite effective in"decolorizing" substances via oxidation.


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The hypochlorite ion (OCl-

), found in manycommercial preparations, is reduced to chlorideions and hydroxide ions forming a basic solution asit accepts electrons from the colored material as

shown below.

OCl- + 2e- + HOH --------> Cl- + 2 OH-

In acidic solutions, H2O2 is one of the mostpowerful oxidizers.

2Fe2+

(aq) + H2O2 + 2H+

(aq) 2Fe3+

(aq) + 2H2O(l)

principle of chemistry: intro

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