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?

 

Sulfuric Acid and Sugar

November 28, 2014, The Canberra Times reported that, "Students were looking on as a teacher conducted an experiment involving sugar and sulfuric acid inside a cabinet when the glass container holding the acid exploded."
The experiment referred to is probably similar to the one shown in the YouTube video below in which concentrated sulfuric acid from a container is poured over sugar in a beaker.

Safety Notes

Sulfuric acid will cause permanent damage if it comes into contact with the eyes or skin. Concentrated solutions of sulfuric acid are extremely corrosive. When sulfuric acid is dissolved in water enough heat is released to make water boil! Carbon monoxide and carbon dioxide are both toxic gases. Sulfur dioxide gas is toxic in high concentration and is a severe respiratory irritant at lower concentration.Some people, especially those prone to asthma, may be especially sensitive to sulfur dioxide. In the presence of moisture, sulfur dioxide forms an acidic, corrosive solution, which in contact with the skin or eyes may lead to burns.

You will notice that the reaction seems to proceed slowly at first. The reaction mixture turns yellow as the reaction begins. This reaction releases heat, it is said to be an exothermic reaction. The heat produced by the reaction then speeds up the rate of further reactions, and, in the video, this is also accelerated by stirring the mixture.

Table sugar is made up sucrose, molecular formula C₁₂H₂₂O₁₁ and structural formula as shown below:

The reaction between sucrose and sulfuric acid in which solid carbon, water vapour and heat are produced is known as a dehydration reaction  :
C₁₂H₂₂O₁₁(s) → 12C(s) + 11H₂O(g)     ΔH = -918.9 kJ mol^-1 Since the enthalpy change for this reaction is negative, the reaction is exothermic, the reaction gives off heat.
Sulfuric acid molecules have a great affinity for water, that is, sulfuric acid will readily and spontaneously dissolve in water. The water produced by the dehydration of sucrose will then be used to dilute the sulfuric acid that is present. This reaction is also exothermic.
H₂SO₄(l) → H₂SO₄(aq)     ΔH = - kJ mol^-1 The heat produced by this reaction also speeds up the rate of the dehydration reaction and subsequent dilution reactions.
Solid carbon is black, so the "black snake" is just carbon.
But what causes the carbon to "rise up" out of the beaker? This must be the result of evolving gases forcing their way through the mixture as the reaction proceeds. The gases that have been identified as products of this reaction  are:

• carbon monoxide (CO) 66% of the dry gas volume (ie, water has been condensed out)
• carbon dioxide (CO₂) 17% of the dry gas volume
• sulfur dioxide (SO₂) 17% of the dry gas volume

Since sulfuric acid does not oxidize carbon, it is most unlikely that the carbon monoxide and carbon dioxide gases are the result of a reaction between the black snake carbon and sulfuric acid. It is much more reasonable to assume that some of the sucrose undergoes dehydration by the sulfuric acid while some this sucrose (and/or some of the resulting intermediate organic products) is oxidized by the sulfuric acid to produce carbon monoxide gas and carbon dioxide gas. During this process, the sulfuric acid will itself be reduced, resulting in the formation of sulfur dioxide gas.

Reference:
http://www.canberratimes.com.au/act-news/students-treated-after-spill-in-burgmann-anglican-school-sciencbe-laboratory-20141128-11vzad.html

Further Reading:
http://ausetute.com.au/safety.html
http://www.ausetute.com.au/mmcalcul.html  
http://www.ausetute.com.au/moledefs.html
http://www.ausetute.com.au/massmole.html
http://www.ausetute.com.au/concsols.html 
http://www.ausetute.com.au/molarvol.html
http://www.ausetute.com.au/molreact.html

Suggested Study Questions:

1.  Describe two hazards in the YouTube Video.
2.  Describe the safety precautions you would take to minimize the risk of the hazards identified in question 1 above.  
3.  Why do you think the concentrated sulfuric acid is added to the sugar rather than adding the sugar to the container of sulfuric acid?
4.  In a typical experiment, 25 mL of 18 mol L^-1 sulfuric acid is added to 50 g of granulated sugar (sucrose). Calculate the amount in moles of :
   • sucrose used
   • sulfuric acid used
5. Calculate the mass of carbon that could be produced in the typical experiment given in question 4.
6. What assumptions have you made in order to calculate the mass of carbon in question 5?
7. Assume that all 50 g of the sucrose is now oxidized at 25^oC to produce carbon dioxide gas and liquid water. What is the maximum volume of carbon dioxide gas, in litres, that could be produced?
8.  Predict what you think might happen if a 50 g of granulated sugar were quickly added to 25 mL of concentrated sulfuric acid in a 100 mL conical flask that was being swirled continuously.
9. Sucrose is a disaccharide, made up of the monosaccharide glucose and the monosaccharide fructose. Starch and cellulose are both polysaccharides, that is, they are made of repeating glucose monomer units. Predict what would happen if you spilled concentrated sulfuric acid on:
   • a paper cup (cellulose)
   • a piece of raw potato (starch)
   • a cotton shirt (cellulose)
10. Design an experiment that could safely be performed in the laboratory to test your predictions in question 9.
11. Do you think that concentrated sulfuric acid will react with the monosaccharide glucose? Explain your answer using a chemical equation.
12.  Design an experiment that could safely be performed in the laboratory to test your prediction in question 11.

Sulfuric Acid - Sodium Hydroxide Titrations

Why does a titration of sulfuric acid using sodium hydroxide have only one equivalence point?
Why isn't the pH 7 at the equivalence point?

These are both excellent questions.

So, we've written a set of resources to help you understand!

AUS-e-TUTE Members should log-in and go to the new tutorial at:
http://www.ausetute.com.au/members/titrh2so4.html
and you can follow the links to the game and test from this page.

Not an AUS-e-TUTE member?
Part of this tutorial is currently available free to non-members for evaluation purposes at
http://ausetute.com.au/titrh2so4.html

Calculating the pH of Sulfuric Acid

How do you calculate the pH of a strong diprotic acid, that is, how do you calculate the pH of sulfuric acid?
I'm glad you asked!
AUS-e-TUTE has just added a new set of resources designed to help you answer this question.

AUS-e-TUTE Members should log-in and go to the links for the Polyprotic Strong Acids tutorial, game and test, on the Test Centre homepage, or, alternatively, go to your AUS-e-TUTE syllabus study guide and follow the links from that.

Not a member?
There is a "free-to-view" tutorial currently available for evaluation purposes at
http://www.ausetute.com.au/polyproticsacid.html

pH of the Manning River

"A POISONOUS plume of acid 'comparable to car batteries' is forming in the Manning River, near Taree in northern NSW, researchers from the University of NSW say." reports Ben Cubby in his article "Acid plume poisons river after floods"  in the Sydney Morning Herald, Thursday 28^th February 2013.
Let's take a look at the chemistry behind the story.
Firstly, Taree, a town located about 3 hours north of Sydney, is surrounded by farm land, land reclaimed from the wetlands. The sulfate ion, SO₄^2-, is commonly found in fertilizers used in commercial farming. Recent rain, and flooding, has concentrated these acidic sulfates in the river.

A little later in the story we find that "Tests carried out by the university's water research laboratory show alarming amounts of acid, with a pH level of two - compared with a normal level of seven - meaning the Manning River water is roughly as acidic as lemon juice."
Chemistry students would realize that there are many factors that can effect the pH of river water, for example, if the river runs through limestone rocks the pH of the water will increase, but if the river runs through areas of peat the pH of the water will decrease.
The pH of river water typically lies within the range of about 6.5 to 8.5.  Water with a low pH is said to be acidic, water with a high pH is said to be basic or alkaline. Most organisms, with the exception of some bacteria, can not live in water with a pH less than 6.5. Similarly, a pH greater than 8.5 also presents problems for the survival of most organisms in rivers.
The juice of a lemon often has a pH of about 2, and the vinegar you buy from the shop will also have a pH around 2. Both lemon juice and vinegar are acidic substances.
On the other hand, oven cleaner has a pH of about 13 and soapy water has a pH of about 12. Both oven cleaner and soapy water are basic solutions (or alkaline solutions).

Is river water with a pH of 2 "comparable to car batteries" as claimed in the story?
Lead-acid batteries, such as those found in cars, contain sulfuric acid, H₂SO₄. Sulfuric acid is a strong acid that undergoes dissociation in water so that an aqueous solution of sulfuric acid contains both hydrogen ions, H⁺, and sulfate ions, SO₄^2-. The acidic river water will contain both hydrogen ions, H⁺, and sulfate ions, SO₄^2-, if sulfate fertilizers have been used on the land where the river runs, so the acid in the car's lead-acid battery and the river water are comparable in that they contain the same ions.
The concentration of sulfuric acid in the lead-battery will usually be between 4 and 5 mol L^-1 (let's just assume its 4.5 mol L^-1 ).
If we assume the complete dissociation of sulfuric acid:
H₂SO₄ → 2H⁺ + SO₄^2-
Then the concentration of hydrogen ions, H⁺, in solution is 2 times the concentration of the sulfuric acid:
[H⁺] = 2[H₂SO₄ ] = 2 x 4.5 = 9.0 mol L^-1
We can calculate the pH of the battery acid, since pH = -log₁₀[H⁺] = -log₁₀[9.0] = -0.95
Battery acid is very, very acidic!
While you might be very happy to put vinegar on your chips (pH~2) and eat them, you  should most definitely NEVER put battery acid on your chips and eat them!

Reference:

 http://www.smh.com.au/environment/conservation/acid-plume-poisons-river-after-floods-20130227-2f6bh.html#ixzz2MA2XQ5AJ

Further Reading:
Calculating pH

Suggested Study Questions:

1. Draw up a table with two headings; acid and base. Place each of the following substances in  the correct column in the table : orange juice (pH =3), baking soda (pH = 9), milk (pH =6), tomato juice (pH =4),  drain cleaner (pH =14), black coffee (pH=5).
2. Calculate the concentration of hydrogen ions in each of the substances in the table, in mol/L
3. Assume a drinking glass has a total value of 250 mL, and that a "full glass" of a drink is actually only 225 mL. Calculate the moles of hydrogen ions found in a "full glass" of
   • orange juice
   • milk
   • black coffee
4. Consider 225 mL of the river water with a pH =2. Calculate the moles of hydrogen ions present.
5. Imagine you took 25 mL of orange juice (pH=3) and diluted it with water to a volume of 500 mL. 
   • Calculate the concentration of hydrogen ions in the diluted solution.
   • Calculate the pH of the diluted solution.
6.  Sometimes cooks heat ingredients to "release their flavour". Acids, like vinegar, tend to have a sour taste. A cook has 200 mL of vinegar (pH=2.2)  in a pan.
   • Calculate the concentration of hydrogen ions present in the solution.
   • On very gentle heating, the volume of the vinegar solution is reduced until it is only 50 mL. Calculate the pH of this concentrated solution.
7. We could prepare a solution of sulfuric acid with a pH of 2 using the acid out of the car's lead-acid battery.
   • Calculate the concentration of hydrogen ions present in 4.5 mol L^-1 sulfuric acid.
   • Calculate the concentration of hydrogen ions present in sulfuric acid with a pH of 2.
   • If you had 10 mL of battery acid, what volume of water would you have to add in order to prepare a sulfuric acid solution with a pH of 2?
8. Imagine the a dam with a volume of 250,000ML and a pH=2. How much water would have to be added to the dam in order for the dam to have a pH=7 ?