Sulfuric Acid Train Derailed

A locomotive and all 26 carriages containing sulfuric acid derailed in north Queensland on Sunday 27^th December 2015.
The 800,000 L of sulfuric acid was bought by Incitec Pivot Limited (IPL) to be used in the production of ammonium phosphate fertiliser at its plant at Phosphate Hill (south of Mount Isa).

Glencore Plc has an agreement with Incitec Pivot Ltd to provide sulfur dioxide from the copper smelter to the Mount Isa acid plant. Sulfuric acid is produced by collecting and cleaning sulfur dioxide before converting it, first to sulfur trioxide, and then to sulfuric acid. The acid plant has the capacity to take up to 80% of the sulfur dioxide emissions from the copper smelter, significantly reducing the emissions of sulfur dioxide into the atmosphere. The sulfuric acid is then taken by train to Phosphate Hill, more than 100 km away.

Phosphate Hill combines a large open-cut phosphate mine with a plant for the production of fertiliser. The proved reserve is 29 Mt at 24.6% P₂O₅. The phosphate ore is first crushed and washed before being dissolved in sulfuric acid to produce phosphoric acid. Gypsum, CaSO₄.2H₂O, a by-product of the process, is stockpiled. The phosphoric acid is converted into ammonium phosphate fertiliser using ammonia gas:
 NH₃ + H₃PO₄ → NH₄H₂PO₄ (known as MAP)
2NH₃ + H₃PO₄ → (NH₄)₂HPO₄ (known as DAP)
The ammonium phosphate is then sent by train to the port at Townsville about 900 km away for shipment.

Wet weather hampered access to the disaster site for several days, but testing of the waters 8 km downstream in Horse Creek revealed changes in acidity. Locally sourced limestone is being used to treat the water.

References:
http://statements.qld.gov.au/Statement/2015/12/31/environmental-testing-continues-around-train-derailment-near-julia-creek
 http://www.abc.net.au/news/2015-12-30/fear-sulphuric-acid-leaked-train-derailed-waterway-julia-creek/7060070

Further Reading
 Copper Smelting
 Electrorefining
 Sulfuric Acid Production
Density Calculations
Percentage Composition 
 Intermolecular Forces
pH Scale 
pH Calculations for Acids  
Neutralisation

Suggested Study Questions:

1. Convert 800 000 L of sulfuric to a volume in:
   • megalitires (ML)
   • kilolitres (KL)
   • millilitres (mL)
2.  Assume the density of this sulfuric acid is 1.84 g mL^-1. What is the mass of 800,000 L of sulfuric acid?
3. Assuming all the sulfuric acid was distributed equally between the 26 carriages, what volume of sulfuric acid was contained in each carriage?
4. Write the chemical formula for each of the following:
• sulfur dioxide
• sulfur trioxide
• sulfuric acid
• sulfurous acid
5.  Convert 29 Mt of phosphate ore to a mass in
   • tonnes (t)
   • kilotonnes (kt)
   • kilograms (kg)
   • grams (g)
6.   A phosphate ore contains 24.6% P₂O₅
   • What mass of P₂O₅ is present in 1 tonne of the ore?
   • What mass of the element phosphorus is present?
   • What mass of the element oxygen is present?
7.  Give the systematic IUPAC name for each of the following:
   • NH₄H₂PO₄
   • (NH₄)₂HPO₄
8. Calculate the percentage by mass of nitrogen in
   • NH₄H₂PO₄
   • (NH₄)₂HPO₄
9. In situations in which too much nitrogen in the fertiliser can adversely affect germination, which phosphate, MAP or DAP, should be used? Explain your answer. 
10. Hygroscopy is the ability of a substance to  attract and hold water molcules from the surrounding environment. Which phosphate, MAP or DAP, would you expect to be more hygroscopic? Explain your answer.
11. Sulfuric acid from the derailed carriages is believed to be leaking into the water of Horse Creek. Do you expect the pH of the creek to be rising or falling? Explain your answer.
12. If the pH of the creek water was 3.0, calculate the concentration of hydrogen ions in the creek water.
13. Explain what the term neutralisation means.
14. Assuming limestone is composed of calcium carbonate only, write a balanced chemical equation for the reaction between sulfuric acid and limestone.
15. Would you describe the chemical reaction described by the equation in question 14 as a neutralisation reaction? Explain your answer.
16. In the laboratory you could use sodium hydroxide to neutralise sulfuric acid. Why isn't sodium hydroxide used to neutralise the sulfuric acid at the train derailment site?