Food Fraud in Australia?

Congratulations to Dr Michael Smith, Associate Professor Mahmud Ashraf, Professor Chris Austin
and Associate Professor Rebecca Lester of  Deakin University on the publication of "Product fraud: Impacts on Australian agriculture, fisheries and forestry industries" (November 2021). This report gives a good, concise, overview of known recent agricultural product fraud from all over the world. While it can make for scary reading, it is a reminder to stay vigilant when buying food. Here is a little taste of what you will find in the report,

"Turmeric is considered highly vulnerable to food fraud, with
frequent incidents of contamination with lead chromate (a
yellow colourant) reported. A study found that seven of nine
turmeric-growing areas in Bangladesh showed evidence
of turmeric adulteration with lead chromate. Levels of lead
exceeded national limits by up to 500 times (24-9-19)."

You can download a copy of the report at the AgriFutures Australia website: https://www.agrifutures.com.au/product/product-fraud-impacts-on-australian-agriculture-fisheries-and-forestry-industry/

Examples of food fraud can be used when teaching chemistry. Students can calculate the concentration of milk or fruit juice after it has been fraudulently diluted, and then compare that to what is stated on the nutrition panel product label. You can learn a lot about the properties of chemical compounds and mixtures by making a fake egg or fake milk. You could used the adulteration of "manuka honey" to teach spectroscopy, or the melamine (1,3,5-triazine-2,4,6-triamine) in milk scandal to teach percentage composition or volumetric analysis. The pedagogical possibilities are limited only by the resourcefulness of the food fraudsters.

If you are looking for some more inspiration, try "Sorting the Beef from the Bull: The Science of food fraud forensics" (Evershed, R., and Temple, N, 2017). And yes, I may have bought it because it has such a great title ... you all know me too well 😉

 

Precipitation Titrations

Have you ever tried to determine the chloride concentration in a water sample using gravimetric analysis? It's pretty tricky! There must be a better way .....
There is .... precipitation titrations (also known as argentimetric titrations or argentometric titrations).
AUS-e-TUTE has just added a new tutorial, game, test, exam and practical activity on this topic for members.
If you are not a member, you can access a "free-to-view" tutorial at
 https://www.ausetute.com.au/pptitration.html

Precipitation Conductometric Titrations

If you have an aqueous salt solution it conducts electricity because of all the ions in the solution. If you add a different aqueous salt solution to this it is possible that a precipitate will form, effectively removing some of the ions in solution so it should be possible to monitor changes in the electrical conductivity of a solution during a precipitation reaction to determine the equivalence point of the reaction. This is known as a precipitation conductometric titration (or as a conductometric precipitation titration) and AUS-e-TUTE has just added a new tutorial, game, test and exam to help our members understand this!
If you are not an AUS-e-TUTE Member, you can currently access a "free-to-view" tutorial on this topic at https://www.ausetute.com.au/conductpptn.html

Colorimetry

I was sitting with some friends drinking tea in glasses.
I noticed some people like "weak" tea and others like their tea "strong".
Technically "weak" tea isn't "weak" at all ... it's really a more dilute solution of tea, while "strong" tea is a more concentrated solution of tea.
But what I noticed most is that "weak" tea is less of a brown colour than "strong" tea, so it ought to be possible to guess the concentration of "tea" in a glass of tea by looking at its colour.
However, I wouldn't have to guess the concentration if I had a colorimeter because a colorimeter would measure the absorbance of each tea solution.
It may seem like a lot of hard work for very little reward ... "I'll like a 0.341 absorbance glass of tea please..." .... but colorimetry is useful tool for measuring the concentration of coloured solutions as you will find out in AUS-e-TUTE's new set of colorimetry resources.
AUS-e-TUTE Members should log-in to use the colorimetry resources listed under "Spectroscopy" and the subheading "Absorption Spectroscopy".
Non-members can access a "free-to-view" tutorial at https://www.ausetute.com.au/colorimetry.html

The man who proved the moon isn’t cheese

Meet Emeritus Professor Ross Taylor AC, the Australian who analyzed the first moon rock samples in 1969, in Volume 46 Number 4 of the ANUreporter,

"With emission spectroscopy you can put a tiny amount of material into the flame and quickly identify any of 70 different elements from the spectral lines they produce. But those 70 elements could produce 100,000 possible lines," he says.
At 11.45am on 28 July, Taylor received the first samples. By 4pm, he delivered preliminary results to a press conference - significantly faster than the usual scientific process and with much more at stake.
The high-speed analysis had not been without hiccups. Taylor almost missed one of the most significant traits of the moon's chemistry, its significantly lower sodium levels than Earth.
The moon is also rich in chromium, which has a spectral line that almost perfectly disguised the low sodium result. Only moments before the press conference Taylor realised the mistake and corrected it.
"It would have ruined my reputation," he says.

Reference:
The man who proved the moon isn't cheese

Further Reading:
http://www.ausetute.com.au/emissions.html 
http://www.ausetute.com.au/flametest.html

Suggested Study Questions
1/ What is an emission spectrum?
2/ How can you produce the emission spectrum of metallic elements at school?
3/ How is the emission spectrum of an element used to confirm the existence of energy levels in atomic structure?
4/ What is a flame test?
5/ How does a flame test differ from emission spectroscopy?
6/ How is a flame test similar to emission spectroscopy?
7/ "With emission spectroscopy you can put a tiny amount of material into the flame and quickly identify any of 70 different elements from the spectral lines they produce." 
Explain how emission spectroscopy can be used to identify different elements.
8/ "But those 70 elements could produce 100,000 possible lines,"
Explain how such a huge number of lines can be produced from what seems like a much smaller number of elements.
9/ "The moon is also rich in chromium, which has a spectral line that almost perfectly disguised the low sodium result"
Explain how a chromium spectral line could disguise the low sodium result.
10/ Imagine you have helped Emeritus Professor Ross Taylor AC analyse these moon rock samples. Produce a scientific poster to communicate the results of this experiment to your class.

Empirical Formula of Magnesium Oxide

It's one of the "classic" experiments in school chemistry, combusting (burning) some magnesium in a crucible to make magnesium oxide.
While the lab questions usually focus on identifying that a chemical change has occurred, and calculating either percentage composition and/or empirical formula of magnesium oxide, I wonder how many students are really thinking about the experiment?
So, AUS-e-TUTE has written a tutorial that (hopefully) will help students think about why certain procedures are followed, and the kinds of errors one can expect.

AUS-e-TUTE members should log-in to use the new tutorial, game and test.

If you are not an AUS-e-TUTE Member, a "free-to-view" tutorial is currently available for evaluation purposes at http://www.ausetute.com.au/mgo.html

Information about AUS-e-TUTE Membership is available at www.ausetute.com.au/membership.html

and you can become an AUS-e-TUTE member at http://www.ausetute.com.au/register.html

Indicators and End Points

What colour is an indicator at the end point ?
At what pH does an indicator change colour?
Why is the colour change for an indicator always given as a range of pH values?

These questions are all addressed in AUS-e-TUTE's new Indicator End Point resources.
Read the tutorial, play the game, do the test and view worked solutions for the questions.

Not an AUS-e-TUTE Member?
There is currently a free-to-view tutorial available at http://ausetute.com.au/endpoint.html

Want to find out more about how an AUS-e-TUTE Membership will help you improve your understanding of chemistry, and, improve your exam results?
Then go to http://ausetute.com.au/membership.html

Ready to join AUS-e-TUTE ?
Go to http://ausetute.com.au/register.html

Got questions?
Contact us at http://ausetute.com.au/contact.html

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

Titration Techniques

What piece of glassware should you use to make a standard solution?
What should you rinse a burette with before filling it with solution?
Should you force all the solution out of a pipette when you use it?

These and many other questions about Titration Techniques have been addressed in AUS-e-TUTE's new tutorials, games, tests, and exams.

Members should log in to use all these new resources which are listed under Volumetric Analaysis, or, use the links from your Syllabus Study Guide in the Members Only Test Centre.

A "free-to-view" tutorial on titration techniques is currently available for evaluation purposes for non-members: http://ausetute.com.au/titrtech.html

Standard Solutions

What is the difference between a primary standard and a secondary standard in volumetric analysis?
What substances can be used as a primary standard?
How do you make a standard solution?

All these questions are answered in AUS-e-TUTE's new tutorial on standard solutions.
Members should log-in and go to the Volumetric Analysis section on the index page, or,
follow the links from your Chemistry syllabus study guide.
Members will also find a game, test and exam as well as tutorial on this topic.
Teachers will find  a worksheet wizard which will let you make, and print off, a worksheet on this topic.

Not an AUS-e-TUTE Member?
There is currently a "free-to-view" tutorial at http://www.ausetute.com.au/titrstand.html

Excel : Line of Best Fit

You can easily use Microsoft Excel to find the equation for the line of best fit for experimental data points.

Remember that the equation of a straight line is y = mx + b
where m is the slope (gradient) of the line and b is the intercept on the y axis (that is, when x =0).

Microsoft excel will calculate both the slope of the line, m, and the y-intercept, b, for you.

First you will need to open up a new excel spreadsheet and set up your data.
Here we have used Row 1 of columns A and B for our headings (x values and y values).
Various values for x and y have then been entered into the cells: 

cell	A	B
1	x values	y values
2	1.02	11.0
3	2.05	21.3
4	2.96	31.2
5	4.12	39.7
6	4.86	53.4

Next, we highlight any two adjacent cells (empty cells) somewhere else in the same spreadsheet, for example A8 and B8

cell	A	B
1	x values	y values
2	1.02	11.0
3	2.05	21.3
4	2.96	31.2
5	4.12	39.7
6	4.86	53.4
7
8

Next to the fx symbol above the cell headings A, B, etc, type in =LINEST(B2:B6, A2:A6)
 then press Ctrl+Shift+Enter simultaneously.
(B2 is the first  y value to be used in the calculation and B6 is the last y value to be used in the calculation. Similarly, A2 is the first of the x values to be used in the calculation and A6 is the last of the x values to be used in the calculation.)
Your spreadsheet should now look this:

cell	A	B
1	x values	y values
2	1.02	11.0
3	2.05	21.3
4	2.96	31.2
5	4.12	39.7
6	4.86	53.4
7
8	10.50606	-0.21918

The number in cell A8 is the slope (m) of the line of best fit.
The number in cell B8 is the y-intercept (b) of the line of best fit, that is, the point with coordinates (0,b)
The equation for the line of best fit for this data is y = 10.50606x -0.21918

In order to draw the line of best fit for the experimental data above, we only need to calculate new values for y using the equation for the line of best fit (that is, the first and last points on the line of best fit).:
given x=1.02 ,then,  y = (10.50606 x 1.02) -0.21918 = 10.5
and x=4.86 , then, y =(10.50606 x 4.86) -0.21918 = 50.8

cell	A	B	C
1	x values	y values	new y values
2	1.02	11.0	10.5
3	2.05	21.3
4	2.96	31.2
5	4.12	39.7
6	4.86	53.4	50.8
7
8	10.50606	-0.21918

Plot the points (1.02, 10.5) and (4.86, 50.8) on the graph of experimental data and draw a straight line between these two points. This is the line of best fit for the experimental data in the table.

Further Activities:
Go to http://www.ausetute.com.au/members/bestfitline.html

1/ Enter the data above into the tool for calculating the two points needed to draw a line of best fit. Check the new y values above, and see what the graph looks like.

Graph the data points in questions 2 to 5 below and draw the line of best fit:

2/ (0.23, 9.75), (0.94, 6.39), (1.77, 5.73), (4.59, 4.91), (11.52, 0.33)
3/

time / min	mass / g
0	102.8
2	73.4
4	48.7
6	27.3
8	10.9

4/

volume / mL	5.0	10.0	15.0	20.0	25.0
mass / g	3.2	7.1	9.4	13.5	14.8

5/ At time 0, the temperature of a reaction mixture was 25^oC. The temperature of the reaction mixture was then recorded every minute for 4 minutes. The results of the experiment were temperatures of 29^oC, 32^oC, 35^oC and 40 ^oC.

HPLC

AUS-e-TUTE has just added new resources for the High Performance Liquid Chromatography (HPLC) topic.
The new resources include a tutorial, game, test and exam.
Go to http://www.ausetute.com.au and log-in to start using these new resources.

The Chemistry Syllabus Study Guides for Queensland, New South Wales, Australian Capital Territory, Victoria, South Australia, and, AP Chemistry (USA and undergraduate) have been updated to include these new resources.

Links to the new resources have also been added from the Class/School Group index page.

Why Use a Volumetric Flask?

In order to prepare an aqueous standard solution, you transfer the solute to a volumetric flask and then you add water "up to the mark", that is, until the bottom of the meniscus lies on the "mark" when viewed at eye-level. You can quickly convince yourself of the need to view the "mark" at eye-level just be preparing your standard solution as above and then changing the angle you view it from.
But what about this need to add water to the solute in this oddly-shaped vessel called a volumetric flask?
Why couldn't you just weigh out the solute into a beaker then add the required volume of water from a pipette?
Or, if the solute is a liquid or a solution, why not just pipette the required volume into a beaker then pipette the required volume of solvent into the same beaker?

So, why not try it?

Experiment (a) For solid solutes such as sodium chloride (table salt) or sucrose ("sugar") just pour the solid into a small DRY measuring cylinder until you have 5 mL for example. Pour this solid into a 100 mL measuring cylinder. Add 50 mL of water from a pipette (you will need to keep swirling the flask while you add the water). Record the volume of the final solution. Repeat the experiment using different volumes of solute and solvent.
Repeat this experiment using sand as the "solute" and water as the solvent.

Experiment (b)  For liquid solutes such as ethanol (ethyl alcohol) or acetone (propanone) use a pipette to place 50 mL of the solute into a 100 mL measuing cylinder then add 50 mL of water from a pipette and record the volume of the final solution. Repeat the experiment using different volumes of solute and solvent.
Repeat this experiment using vegetable oil as the "solute" and water as the solvent.

If a solute dissolves in a solvent, the volume of the final solution is not equal to the volume of the solute plus the volume of the solvent. Sometimes adding a solute to a solvent results in a solution with a volume less than that of the solvent + solute, and sometimes adding a solute to a solvent results in a solution with a volume greater than that of the solvent + solute. Right now, there are no good, general theories to explain this behaviour! But it is because of this that we use that oddly shaped piece of glassware called a volumetric flask when we make up a standard solution.

Concentration of Calcium Ions in Hard Water

AUS-e-TUTE has just added new complexometric titration resources for the determination of calcium ions in hard water.
Members should log-in to see the new tutorial, game, test and drill.

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 ?

Neutral pH?

We hear this term a lot, often in advertising. But what does it mean?

From a Chemist's point of view, there are two different concepts involved in this seemingly harmless "neutral pH" expression. These two different concepts are:

• neutral
• pH

Let's take a look at the Chemist's definition of neutral first.
A solution is neutral if the concentration of hydrogen ions, [H⁺], is equal to the concentration of hydroxide ions, [OH^-].
Chemists often use square brackets to denote concentration, the concentration of  hydrogen ions can be written as [H⁺] and the concentration of hydroxide ions can be written as [OH^-].
So, for a neutral solution:

[H⁺] = [OH^-] = neutral solution 

Pure water is an excellent example of a neutral substance.

Some of the water molecules, actually very few of them, dissociate to form hydrogen ions and hydroxide ions:

H2O

H+ + OH-

Every time a water molecule dissociates, it produces one hydrogen ion, H⁺, and one hydroxide ion, OH^-, so that the concentration of hydrogen ions is always the same as the concentration of hydroxide ions.
Therefore, pure water is always neutral!

The pH of a solution is a measure of the hydrogen ion concentration in the solution. pH can be defined as:

pH = -log₁₀[H⁺]

This equation can be used to calculate the pH of our neutral water, but only if we know the concentration of  hydrogen ions in the water.

The concentration of hydrogen ions in water is not constant!

The concentration of hydrogen ions in water depends on the temperature of the water!
The dissociation of water molecules requires energy:

H2O + energy

H+ + OH-

If you put more energy into the system by heating it, then more water molecules dissociate, the concentration of hydrogen ions increases and the concentration of hydroxide ions also increases.
If you take energy away from the system by cooling it, then fewer water molecules dissociate, the concentration of hydrogen ions decreases and the concentration of hydroxide ions also decreases.
If we were to measure the concentration of hydrogen ions in pure water at various temperatures, we would find the following values:

Water temperature	[H+] x 10−7 M	pH
0°C	0.32	7.50
10°C	0.55	7.26
18°C	0.84	7.08
25°C	1.10	6.96
30°C	1.34	6.87
50°C	2.82	6.55
60°C	3.55	6.46
70°C	4.60	6.34
80°C	5.92	6.23
90°C	7.28	6.14
100°C	8.54	6.07

So what is the pH of water?
The pH of water is dependent on the temperature of the water.
Water is neutral for every value of pH because the concentration of hydrogen ions is always equal to the concentration of the hydroxide ions.
We can ONLY talk about the pH of water IF we state the temperature of the water.
For example, we can talk about water having a pH of approximately 7 at 25^oC, or we could say that the pH of water is approximately 6 at 100^oC.
Pure water is always neutral.
Pure water is neutral at 25^oC.
Pure water is neutral at 100^oC.

As Chemistry students, what we can't say is that water has a pH of 7, or that a neutral aqueous solution has a particular pH, unless we state the temperature of the system.

Further Reading:
Definitions of Acids and Bases
pH
Dissociation Constant for Water

Suggested Study Questions:

1. Plot a graph of temperature versus concentration of hydrogen ions in water. Describe the shape of the line, and write a generalization that links hydrogen ion concentration and temperature.
2. Plot a graph of temperature versus pH of water. Describe the shape of the line and write a generalization linking the  temperature of water and its pH.
3. Use your graph to find the pH of water at:
   • 12^oC
   • 22^oC
   • 32^oC
4. Construct a table giving the concentration of hydroxide ions in water at each of the temperatures shown above.
5. Plot a graph of temperature versus concentration of hydroxide ions in water. Describe the shape of the line, and write a generalization linking hydroxide ion concentration in water and temperature.
6. Use your graph to find the concentration of hydroxide ions in water at:
   • 12^oC
   • 22^oC
   • 32^oC
7. Explain why water is neutral at all temperatures.
8. Explain why the pH of water varies with temperature.

Arsenic Tests

Somewhere around the 8th century, an Arab alchemist produced white arsenic trioxide (As₂O₃) from realgar, a naturally occurring arsenic sulfide mineral, As₄S₄:
As₄S₄ + 7O₂ → 2As₂O₃ + 4SO₂ Arsenic trioxide became one of the most widely administered poisons in history, and therefore, it became necessary to find reliable tests to show whether or not arsenic was present in a sample of food or drink, or whether it was present in a corpse.

In 1775, Carl Wilhelm Scheele treated arsenic trioxide with nitric acid and zinc which resulted in arsine gas (AsH₃), zinc nitrate and water:
As₂O₃ + 6Zn + 12HNO₃ → 2AsH₃ + 6Zn(NO₃)₂ + 3H₂O Arsenic was said to be present if an odour of garlic was produced because arsine gas smells a lot like garlic.

In 1787, Johann Metzger used a carbon reduction method to produce carbon dioxide gas and solid arsenic from arsenic trioxide and carbon:
2 As₂O₃ + 3 C → 3 CO₂ + 4 As As the arsenic trioxide is heated with charcoal, an "arsenic mirror" forms on the charcoal.

In 1785, Samuel Hahnemann produced a bright yellow precipitate of arsenic trisulfide, As₂S₃, by passing a stream of hydrogen sulfide gas, H₂S, through an acidified arsenic solution.

In 1836, James Marsh designed an apparatus that would detect and measure arsenic.
The sample is placed in a flask with arsenic-free zinc and sulfuric acid.
Arsine gas forms:

As₂O₃ + 6 Zn + 6 H₂SO₄ → 2 AsH₃ + 6 ZnSO₄ + 3 H₂O

The arsine gas is fed through a drying tube to a glass tube which is heated.
Arsine deomposes on heating, forming elemental arsenic which is a shiny black substance:

2 AsH₃ → 3 H₂ + 2 As

By placing a cold surface at the end of the heated tube it is possible to condense this arsenic, which forms a black "mirror".

http://www.youtube.com/watch?v=-vUZdAwgl2g

Today, these "wet" methods of chemical detection have been superceded by instrumental analysis. e Atomic absorption spectroscopy (AAS)  can now be used to determine not only the presence of arsenic, but also how much arsenic is present.

Further Reading:
Solubility Rules
Writing Precipitation Equations
Gravimetric Analysis
AAS
Oxidation and Reduction 
Carbon Reduction Methods

Suggested Study Questions:

1. Give the oxidation state (number) for arsenic in each of the following:
   • As₂O₃
   • As₄S₄
   •  AsH₃
   • As
2. For the reaction: As₄S₄ + 7O₂ → 2As₂O₃ + 4SO₂ which element, or elements, have been oxidized?
3.  Consider the reaction: 2 As₂O₃ + 3 C → 3 CO₂ + 4 As
   Is arsenic likely to be more or less active than carbon?
4. Write a possible net ionic equation for the reaction in which arsenic ions react with  hydrogen sulfide gas to produce a precipitate of arsenic trisulfide.
5. Consider the reaction: 2 AsH₃ → 3 H₂ + 2 As which results in the formation of a shiny black "mirror" of arsenic.
   • Has arsenic been oxidized or reduced?
   • Has hydrogen been oxidized or reduced?
   • If 1 mole of arsine gas decomposes completely, how many moles of hydrogen gas would be produced?
   • At 0^oC and 100 kPa, what volume of gas would be produced by the thermal decomposition of 25 moles of arsine?
   •  At 0^oC and 100 kPa, what mass of arsenic would be deposited after  the thermal decomposition of 150 mg of arsine.
   • At 25^oC and 100 kPa, what mass of arsine will decompose to produce 0.05 L of hydrogen gas?
   • A sample of gas containing arsine produces an "arsenic mirror" containing 0.02 g of arsenic. What mass of arsine was present in the gas sample?

Green Hair

Imagine you are living in a small town in Sweden.
You go to bed one night, naturally blonde.
When you wake up in the morning and look in the mirror your blonde hair has turned green!
Not only that, but your naturally blonde neighbour also has green hair!

This actually did happen in 2011, and, no doubt, caused a certain amount of distress.

Where would you begin in order solve the "green hair" mystery?
What could turn hair green?

Blonde hair often turns green after swimming in chlorinated pool water.
Copper, used in compounds to reduce algae growth in water, can be present in concentrations of about 0.5 ppm in pool water. When bleach (often sold as "liquid chlorine") is added to the pool water it oxidizes the copper resulting in a pretty green colour, and the oxidized copper binds to the proteins in the hair.
If you happen to have copper pipes in your bathroom, you've probably seen "green stains" on the pipes where the copper has been oxidized.

So, back to the story in Sweden.
Samples of drinking water were taken from a number of homes in order to measure the amount of copper present but the concentration of copper in the water did not exceed the recommended guidelines (that is, the copper ion concentration was less than 1 ppm).

However, in new houses, when hot water was left overnight and tested the next morning, the concentration of copper in the water increased dramatically. On further investigation it was discovered that the hot water pipes in new houses lacked the coating that the pipes in older houses had. So, overnight, when the water in the pipes was still and not being continuously "flushed" through the pipes, copper particles were being added to the water.

For solving the "Swedish Green Hair Mystery" Johan Pettersson was rewarded with a 2012 Ig Nobel Prize for Chemistry.


References:
http://www.thelocal.se/37994/20111217/
http://www.improbable.com/ig/winners/#ig2012

Further Reading 
http://www.ausetute.com.au/waterana.html 
http://www.ausetute.com.au/aas.html 
http://www.ausetute.com.au/partspm.html 
http://www.ausetute.com.au/concsols.html 
http://www.ausetute.com.au/weightpc.html 
http://www.ausetute.com.au/corrosion.html 

Suggested Study Questions:

1. Describe 2 methods you could use to detect the presence of copper ions in water.
2. Describe the process by which Atomic Absorption Sepctroscopy (AAS) could be used to measure the concentration of copper ions in a water sample.
3. Describe a way that you could prevent copper from entering the water in the copper water pipes in this Swedish town.
4. Copper is often present in soils at a concentration of around 50 ppm. What mass of copper would be present in 0.5 tonne of soil?
5. A particular pool contains 40,000 L of water. If the pool water contains 0.5 ppm copper ions, what is the concentration of copper ions in mol L^-1 ?
6. Chocolate can contain 10 mg/kg  copper. What mass of copper is present in a 250 g bar of chocolate?
7. Doses of copper that exceed 50 mg/kg of body mass can be lethal. Calculate the mass of copper that would be the lethal limit for an 80 kg adult.
8. What advice could you give the inhabitants of this Swedish town in order for them to avoid having green hair?

Arsenic in Air, Hair and Water

On Saturday 20^th August 2011, the Sydney Morning Herald reported that the chemical company Orica "discharged up to 1.2 megalitres of effluent containing traces of arsenic above its environmental protection licence cap yesterday afternoon".
Arsenic is toxic, it disrupts the transport of energy within cells and metabolism. The minimal lethal dose of arsenic in adults is about 1mg per kilogram of body mass per day, but arsenic trioxide is about 500 times more toxic than pure arsenic.

The Romans used arsenic compounds, especially naturally occurring arsenic sulfides, as medicines. The Roman writer Dioscorides (40-90) wrote in De Materia Medica (Medical Matters) that arsenic sulfides could be used to treat warts and skin eruptions, but warned that the remedy could cause the patient's hair to fall out! It is believed that Agrippina used arsenic trioxide to murder her husband so that she could marry her uncle, the Emporer Claudius.
At about the same time, the Chinese were using arsenic compounds to kill flies and rodents while Indians were using them to preserve paper from attack by insects.

In medieval Europe, arsenic trioxide was being used to treat malaria, while arsenic sulfides were used to treat arthritis, asthma, tuberculosis, and diabetes.

In 1809, Dr. Fowler's Solution first appeared in the London Pharmacopoeia, and it was considered to be a cure for almost everything! Fowler's solution was a mixture of potassium arsenite in lavender water. It was prepared by dissolving 10g of arsenic trioxide and 7.6g of potassium hydrogen carbonate in 1L of distilled water, then adding a little alcohol and lavender oil. The maximum single dose recommended was 0.5mL of Fowler's Solution which could be added to a glass of water or wine.

Arsenic was very common in European households up until the late 19^th century.
Arsenic was being used to provide brilliant colours in dyes and paints:

• yellow orpiment, As₂S₃ (a mineral in use since Ancient times)
  
• red realgar, As₄S₄ (a mineral in use since Ancient times)
  
• Scheele's Green, copper arsenite, CuHAsO₃ (first produced in 1778)
• Emerald Green, a combination of copper acetate and copper arsenite (first produced in 1822)

In the 19^th century, arsenic-based green colours were being used to colour paint, wallpaper, soap, lampshades, children's toys, candles, soft furnishings, and even food. By the late 19th century, Gosio's disease, sickness resulting from breathing the air in rooms decorated with arsenic compounds, was identified. The deadly vapour was not identified as trimethylarsine until the 1930's.

Napoleon Bonaparte died on 6^th May 1821 at Longwood House on Saint Helena. Samples of Napoleon's hair were analysed in 1995 and were found to contain between 33ppm and 17ppm of arsenic, the maximum "safe" limit is currently considered to be about 3ppm and the normal level is about 1ppm. While some people believe that Napoleon was deliberately poisoned,it is possible that green furnishings at Longwood House could be to blame for the high levels of arsenic in his body.

Arsenic has also been discovered in the hair of "mad" King George III of Great Britain who died in 1820. In 2003, samples of the King's hair found in the Science Museum London were analyzed and found to contain about 17ppm arsenic.

in 1904, Julius Nieuwland added an aluminium chloride catalyst to a mixture of acetylene and arsenic trichloride to produce an arsenic compound that came to be known as Lewisite. Unfortunately Nieuwland had taken no safety precautions so he breathed in some of the vapour, was taken ill and spent the next few days in hospital. During World War I, Winford Lewis heard about Nieuwland's earlier experiment, and he learnt how to produce the toxic compound under carefully controlled conditions so that it could be used as a weapon. By November 1918, the USA was shipping deadly Lewisite to Europe. Lewisite was then used by the Japenese against the Chinese in Manchuria in 1940, and by Saddam Hussein in the Iran-Iraq war in the 1980's.

Tube wells, drilled in the 1970's in West Bengal, India and Bangladesh, were installed in a drive by the United Nations Children's Fund (UNICEF) to provide safe drinking water for a population that had traditionally taken its water from contaminated streams, rivers, and ponds, and therefore suffered from water-borne diseases such as gastroenteritis, typhoid and cholera. By 1983 the population, more than 30 million people, were showing signs of arsenic poisoning. The water in many of the wells had arsenic levels of between 50ppb and 4000ppb. At the time, the World Health Organisation (WHO) stated that drinking water should not contain more than 10μg/L.

In the 20th century, copper arsenite, also known as Paris Green, and lead arsenate have been used as a horticultural spray to kill moths on apple trees, but these compounds have now been phased out. Chromium copper arsenate, used to treat wood to prevent it rotting and being eaten by termites, has been phased out in some countries like Australia, Canada and the USA, but is still being used in others. In the electronics industries, arsenic is added to silicon and germanium semiconductors to provide electrons to the crystal lattice. Gallium arsenide is a semi-conductor which has the ability to convert electric current to laser light, so this is a growing use for the world's arsenic.

Further Reading
Volume Conversions
Parts per Million Concentration
W/V %
Molarity
Writing Ionic Formulae
Oxidation States (Numbers)

Study Questions:

1. Convert 1.2 megalitres to a volume in
   • litres
   • kilolitres
   • gigalitres
   • millilitres
2. "The minimal lethal dose of arsenic in adults is about 1mg per kilogram of body mass per day". Calculate the mass of the dose of arsenic that would be lethal in each case below:
   • 1 dose given in 1 day to a man weighing 90kg
   • 1 dose given in 1 day to a woman weighing 65kg
   • 1 dose given in 1 day to a child weighing 30kg
   • 1 dose given 3 times a day with meals to a person weighing 70kg.
3. The arsenite ion has the formula AsO₃^3- and the arsenate ion has the formula AsO₄^3-.
   • Write the formula for potassium arsenite
   • Write the formula for potassium arsenate
   • Write the formula for calcium arsenite
   • Write the formula for barium arsenate
   • Write the formula for ammonium arsenate
   • Write the formula for copper (II) arsenite
   • Write the formula for lead (II) arsenate
     
4. Give the oxidation state (number) of arsenic in each of the following:
   • AsO₃^3-
   • AsO₄^3-
   • As₂S₃
   • As₄S₄
   • HAsO₃^2-
   • As₂O₃
   • AsCl₃
5. Calculate the concentration of arsenic ions in mol/L in 1L of Fowler's Solution using the recipe provided in the article (assume all the arsenic present is in the form of arsenic ions).
6. For a 0.5mL dose of Fowler's Solution, calculate
   • the mass of arsenic present in grams
   • the mass of arsenic present in milligrams
   • the concentration of arsenic in parts per million
7. Assuming 10g hair samples were tested for arsenic
   • What is the mass of arsenic present in a healthy persons hair if the normal level is 1ppm?
   • The safe limit for arsenic in hair is 3ppm, what mass of arsenic is this equivalent to ?
   • Napoleon's hair was found to contain between 17ppm and 33ppm arsenic. Convert each of these concentrations to a mass of arsenic.
8. For the water tested in the Asian tube wells:
   • convert 4000ppb to a concentration in ppm
   • calculate the mass of arsenic in 1L of water if the concentration is 50ppb
   • convert the safe limit for arsenic in drinking water, 10μg/L, to a concentration in mol/L
   • calculate the mass of arsenic present in 1L of drinking water that contains 10μg/L arsenic
     

Reference

http://www.smh.com.au/environment/orica-admits-arsenic-spill-into-river-20110819-1j2nz.html#ixzz1Vcq8n2jf

Ocean pH

Coccoliths are very small shells of calcium carbonate that form around a number of species of algae. Algae play an important role in the global carbon-oxygen cycle and thus in our ecosystem. Scientists at the Nano-Science Center, University of Copenhagen, have measured how individual coccoliths react to water with different degrees of acidity.

Coccoliths which have a mass of about 500 pg (0.0000000005 g), were weighed before and after they had been immersed in water with different acidities. The results enable the scientists to say something about how important the water acidity is for the marine environment.

The world's oceans are acidifying due to our emissions of carbon dioxide. Over time the pH of the Earth's oceans is decreasing:

Time	pH
18th century	8.179
Recent past (1990s)	8.104
Present levels	~8.069
2050 (estimated)	7.949
2100 (estimated)	7.824

Coccoliths are protected from dissolution by a very thin layer of organic material that the algae form, even though the seawater is extremely unsaturated relative to calcite (calcium carbonate). The protection of the organic material is lost when the pH is lowered slightly. In fact, it turns out that the shell falls completely apart when experiments are done in water with a pH value of 7.8, the pH that many researchers believe will be the found in the world oceans in the year 2100.

Reference:
T. Hassenkam, A. Johnsson, K. Bechgaard, S. L. S. Stipp. Tracking single coccolith dissolution with picogram resolution and implications for CO2 sequestration and ocean acidification. Proceedings of the National Academy of Sciences, 2011; DOI: 10.1073/pnas.1009447108\

Further Reading:
Carbon Cycle
Combustion of Hydrocarbons
Acid Rain
Mass Conversions
pH Calculations
Acid Dissociation Constants (Ka)

Study Questions:

1. Write the formula for:
   
   • carbon dioxide
   • calcium carbonate
2. Calculate the percentage composition of
   
   • carbon dioxide
   • calcium carbonate
3. Write a balanced chemical equation to show the production of carbon dioxide from the combustion of methane (a fossil fuel).
4. Assuming 100 tonnes of methane gas were combusted under standard laboratory conditions:
   
   • What is the maximum mass of carbon dioxide that could be produced?
   • What volume would this mass of carbon dioxide occupy?
5. Coccoliths have a mass of about 500 pg. Convert this to a mass in:
   • milligrams
   • micrograms
   • nanograms
   • kilograms
6. The current pH of ocean water is approximately 8.069. Assuming the temperature of the oceans to be 25^oC, calculate the current:
   • hydrogen ion concentration of ocean water
   • hydroxide ion concentration of ocean water
   • pOH of ocean water
   
   
7. In 2100, the pH of ocean water is predicted to be 7.824. Assuming the temperature of the oceans to be 25^oC, calculate the:
   • hydrogen ion concentration of ocean water in 2100
   • the hydroxide ion concentration of ocean water in 2100
   • the pOH of ocean water in 2100
   • the increase in hydrogen ion concentration between now and 2100
     
   
   
   
8. For the reaction: H₂CO₃ HCO₃^- + H⁺ K_a = 4.5 x 10^-7
   
   • Is H₂CO₃ a strong acid or weak acid? Explain your answer.
     
   • Calculate the concentration of H⁺
   • Calculate the pH of the solution.
   • Calculate the pOH of this solution at 25^oC.
   • Calculate the concentration of hydroxide ions at 25^oC.
   • Explain what impact an increase in hydrogen ion concentration would have on this equation.