HSC Chemistry: Why Do We Need to Monitor the Environment?


This is part of the HSC Chemistry course under Module 8 Section 1: Analysis of Inorganic Compounds. 

HSC Chemistry Syllabus

  • analyse the need for monitoring the environment

Why Do We Need to Monitor The Environment?

This video will show why there is a need to monitor the environment, exploring the environmental implications of:

  • Carbon oxides
  • Nitrogen oxides
  • Sulfur oxides
  • Phosphorus
  • Heavy metals e.g. lead and mercury
  • Calcium and magnesium ions in hard water


Environmental Monitoring Analysis 

Why Do We Monitor for Oxides in Air?

Analysing air quality and the oxides which may be present within them is important because of the health and environmental risks which they pose. 

  • Carbon oxides
    • Carbon can either exist as carbon monoxide or carbon dioxide in the environment. 
    • The complete combustion of hydrocarbon fuels produces carbon dioxide while its incomplete combustion can lead to the production of carbon monoxide and soot. 
    • Soot which are solid carbon particulates are a carcinogen meaning that they contribute to the causation of cancer. 
    • Carbon monoxide is a health risk as it is both odourless and toxic, interfering with the body's ability to transport blood throughout the body. 
    • Carbon dioxide poses a problem to our environment because it contributes to global warming as it is a greenhouse gas, and also leads to ocean acidification - a lowering in the pH of the ocean.
      • the carbon dioxide will react with and dissolve in water to form carbonic acid

$$CO_2(g) + H_2O(l) \rightleftharpoons H_2CO_3(aq)$$ 


  • Sulfur oxides
    • The burning of fossil fuels also leads to the production of sulfur dioxide gas. 
    • SO2 acts as both a health hazard, causing irreversible respiratory problems and also an environmental hazard as it is responsible for the formation of acid rain (reduction in ocean’s pH) through forming sulfur trioxide when reacting with oxygen. 

$$2SO_2(g) + O_2(g) \rightarrow 2SO_3(g)$$

$$SO_3(g) + H_2O(l) \rightarrow H_2SO_4(aq)$$


  • Oxides of nitrogen
    • Oxides of nitrogen can also be produced from the burning of fossil fuels. Both nitrogen oxide and nitrogen dioxide poses a range of environmental hazards. 
    • Nitrogen dioxide is broken into free radicals when exposed to sunlight (UV light). These reactive radical species can react with hydrocarbons and oxygen in the air to form ozone – photochemical smog. The smog decreases visibility.
    • Nitrogen monoxide can lead to the formation of nitrogen dioxide which in turn contributes to acid rain. 

$$2NO(g) + O_2(g) \rightarrow 2NO_2(g)$$

$$2NO_2(g) + H_2O(l) \rightarrow HNO_3(aq) + HNO_2(aq)$$


  • Haloalkanes
    • Haloalkanes originate from the usage of a variety of common aerosol items. However, if not processed appropriately, can reach Earth’s atmosphere to generate free radicals. These free radicals in turn react with the ozone (O3), leading to its depletion.


Why Do We Monitor Soil Quality?

Whilst nutrients such as nitrogen and phosphorous are essential for plant growth, overuse of fertilisers causes them to become excessive. They can be carried into water ways by rainwater run off, leading to eutrophication which starves aquatic ecosystem of sunlight and oxygen.

Plants also require trace amounts of metals such as zinc, copper and iron in the soil. Overusing fertilisers also leads to these elements becoming excessive, ultimately hindering plant growth and posing risks of food shortage.


Why Do We Monitor Water Quality?

Monitoring of water quality includes measuring its hardness, heavy metal content, and pH.

  • Hardness 
    • The hardness of softness of water refers to the concentration magnesium and/or calcium ions. 
    • Water hardness is usually needed to be quality controlled for usage in daily water supply. Harder water tends to be better for drinking. However, it cannot lather with soap and instead produces a scum that clogs up pores and is harsh on the skin.
    • Softer water is better for lathering soap as it does not form scum. Though, it has lower pH which can corrode metal pipes it runs through. 


  • Heavy metals
    • Heavy metals pose a toxicity problem for humans as the ingestion of an excessive amount can lead to a variety of issues including neurological and physical effects. 
    • Lead (Pb2+) and mercury ions (Hg2+) are toxic to humans leading often to neurological damages. Both of these metals can lead to retardation of the brain with mercury having the ability to bypass the blood-brain barrier and placental membrane. 
    • Pb2+ ions can originate from lead-based pigments (e.g. paint) and fuels.
    • Hg2+ ions can originate from chemical factories and medical devices (e.g. thermometer).


  • pH
    • Monitoring H+ ions are essential for maintaining aquatic ecosystems e.g. fish, coral reef
    • This is because a large majority of aquatic lifeforms have exoskeletons which consist of the compound calcium carbonate. Carbonate compounds dissolve in acidic solutions and the decrease in pH can make the reformation of these shells more difficult. 
    • Other reasons include the sensitivity which aquatic lifeforms have to pH - Coral bleaching in the Great Barrier Reef is an example of an attribution of water acidification as the photosynthesising microorganisms which give corals their colour are expelled. 


  • Agricultural use
    • In agriculture, water is utilised to grow fresh produce. As previously discussed, soil quality is also monitored as a major factor in agricultural success.
    • Phosphate ions which are an essential nutrient also exist in natural waterways e.g. rivers, at low concentrations for the growth of aquatic plants. However excessive phosphate levels in the waterways promote algal growth ('bloom') in an event which is called eutrophication, negatively impacting the ecosystem.