Sunday, November 18, 2012


On Monday 12th November 2012, a Queensland farmer was out spraying paraquat, one of the most widely used herbicides (weedkillers) in the world. The pressure pump unit released and sprayed paraquat into the farmer's mouth. Tragically, 24 hours later the farmer died.

Because paraquat is a highly toxic chemical, it is available in Australia and the United States only to trained users and is not supplied for home or garden use. Even though it is so toxic to humans, it is still widely used because it kills a wide range of grasses and weeds very quickly and becomes biologically inactive on contact with the soil.

Paraquat is the trade-name for 1,1'-dimethyl-4,4'-bipyridinium dichloride. The structural formula is shown on the right.
1,1'-Dimethyl-4,4'-bipyridinium dichloride is a yellow solid at room temperature and pressure and smells faintly like ammonia.

 Commercially, paraquat is available as a solution at a concentration of 250 g/L. This is further diluted by the farmer before applying it to the fields.


Further Reading 
Empirical and Molecular Formula 
Relative Molecular Mass
Concentration of Solutions (molarity)
Structural Isomers

Suggested Study Questions:
  1. Give the molecular formula for paraquat.
  2. Give the empirical formula for paraquat.
  3. Calculate the molecular mass of paraquat.
  4. Calculate the moles of paraquat present in 8 L of commercially available paraquat solution.
  5. Draw the structural formula for 2 possible structural isomers of paraquat.
  6. Paraquat is often sold as the chloride salt as shown in the structural formula in the article above. It can also be sold as the sulfate salt. Draw a possible structural formula for the sulfate salt form.
  7. In the instructions for use, the manufacturer of paraquat stresses that only clean water, water free of clay or silt, should be used to dilute the paraquat solution. Why is it so important to use clean water?
  8. Suggest some safety precautions that farmers should take when preparing and using paraquat.

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