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

Name and Formula of Inorganic Acids

There are systematic ways to name inorganic acids, however, for many acids no-one uses these systematic names because the "acid name" for these particular acids has been in use for a very long time. So, IUPAC recognises the "acid name" for a number of acids.
AUS-e-TUTE has just added a new tutorial, game, test, quiz and worksheet wizard, as well as a card game, to help you give the name and molecular formula of these acids. AUS-e-TUTE members should log-in to use these new resources.

If you are not an AUS-e-TUTE member, there is a "free-to-view" tutorial currently available at
https://www.ausetute.com.au/acidnames.html

Don't forgot to download our free "Inorganic Acid Names Card Games" when you visit!
(includes instructions for 3 games and a set of game cards).

Name and Formula of Inorganic Molecules

Non-metallic elements combine to produce covalent compounds, that is, molecules in which the atoms are held together by covalent bonds.
But do you know how to name these molecules using IUPAC recommendations?
Can you write the formula for these molecules using IUPAC recommendations?

AUS-e-TUTE has just added new resources on these topics.
AUS-e-TUTE members should log-in to access the tutorials, games, tests, exams, drills.
AUS-e-TUTE class and school group members also have access to the online quizzes.
Teachers registered with a class or school group can also access the worksheet wizards (instant worksheets, with answers, at the click of button!).

If you are not an AUS-e-TUTE member, there are two "free-to-view" tutorials currently available:

Naming Binary Inorganic Non-metallic Compounds

Molecular Formula of Binary Inorganic Non-metallic Compounds

Writing the Formula of an Inorganic Salt

Organic chemistry deals with compounds of carbon.
Inorganic chemistry deals with compounds of any other element.
One of the earliest known classes of inorganic compounds were salts.
Salts are binary, ionic compounds, that is, salts are made up of two ions:

• a positively charged ion called a cation
• a negatively charged ion called an anion 

The International Union of Pure and Applied Chemistry (IUPAC) is establishing rules to help us name, and write the formula, for compounds.
In an earlier tutorial we looked at how we name inorganic salts, in this tutorial we look at how to write the formula of an inorganic salt.

Naming Salts

How do you name a salt?
There are several different ways to name salts (binary inorganic ionic compounds).
The most common method used in school as an introduction to naming inorganic compounds is based on compositional nomenclature.
AUS-e-TUTE has a step-by-step guide to how to name a salt if you know the formula of the salt:
https://www.ausetute.com.au/namiform.html

IUPAC Name and Formula of Cations

Naming chemical compounds can be a bit tricky. One of the biggest problems is that people started naming compounds before they understood what they were! And, the problem just gets bigger as we discover new classes of compounds.
Even naming simple binary inorganic ionic compounds (well ... salts!) can produce enormous headaches.
Well, we've started sorting through some of the mess, starting with a whole let new set of resources for writing the formula of cations and naming cations using the current IUPAC recommendations.
Members should log-in to AUS-e-TUTE to use the new resources, but if you are not a member you can go to the "free-to-view tutorial" at https://www.ausetute.com.au/cations.html

Ammonium Nitrate Explodes

On Friday 6^th September 2014, a truck carrying 56 tonnes of ammonium nitrate exploded after rolling over near a bridge on the Mitchell Highway between Cunnamulla and Charleville in the Australian State of Queensland. Eight people were injured, and the Mitchell Highway has been closed "indefinitely".

The most important use for ammonium nitrate is as a fertilizer, but it can also be used as an explosive. An explosion results when ammonium nitrate is brought into contact with heat, a source of ignition such as a spark, or, with reducing agents. Unfortunately, explosions of ammonium nitrate are not rare. A massive explosion of ammonium nitrate on 17^th April 2013 resulted in the death of 15 people, and the destruction of the West Fertilizer Company storage and distribution facility in Texas, USA.

Ammonium nitrate can be produced in commercial quantities by reacting ammonia gas with  nitric acid.

Reference: 
http://www.brisbanetimes.com.au/queensland/truck-explosion-injures-eight-closes-mitchell-highway-20140906-10dam3.html

Further Reading
Naming Ionic Compounds 
Writing Ionic Formula 
Mole Definitions 
Molar Gas Volumes

Suggested Study Questions:

1. Write the chemical formula for ammonium nitrate 
2. Explain why this compound is considered to be an ionic compound.
3. Write a word equation for the reaction between ammonia gas and nitric acid to produce ammonium nitrate
4. Write a balanced chemical equation for the reaction in question 3.
5. Ammonium nitrate decomposes in to N₂O and H₂O when heated. Write a balanced chemical equation for this reaction.
6. Calculate the molar mass of ammonium nitrate.
7. Calculate the moles of ammonium nitrate present in the truck.
8. Assuming that the decomposition of ammonium nitrate results only in gaseous products, what volume of gas at 25^oC and 100 kPa would be released by ammonium nitrate in the truck?
9. Assume the truck could carry a load with a volume of 30,000 L. Can you suggest a reason why rapidly decomposing ammonium nitrate could explode, destroying the truck, the bridge and the road?

Gallium Practical Jokes

If you ask a Chemist what their favourite metal is, the chances are they will answer gallium.

Historically, gallium is significant because it was one of the elements that Dmitri  Mendeleev predicted the properties of, before the element had even been discovered! Mendeleev called the element ekkaaluminium.

Gallium has gained commercial value because gallium compounds such as gallium arsenide, GaAs, are important semiconductors in the electronics industry.

But the reason many Chemists like gallium is because of its interesting physical properties.
Gallium is a silvery metal with a metallic lustre that looks a lot like silver. Unlike silver however, gallium is not found as the element in nature. Gallium compounds occur in minute quantities in bauxite (an aluminium ore) and sphalerite (a zinc ore) and can be extracted from these ores by smelting.
The melting point of gallium is about 29.8^oC and its boiling point is about 2204^oC. This means that at temperatures between 29.8^oC and 2204^oC gallium is a liquid. Or put another way, if you have some gallium in a test tube on a hot summer's day in Sydney, or Miami, or anywhere where the temperature gets above 30^oC, what you will see is a puddle of molten metal, but if you take the molten gallium back into an air-conditioned room where the temperature is likely to be less than 25^oC, the gallium will freeze again.
And this is the basis of the disappearing spoon trick as shown in the video.

At temperatures below its melting point, gallium is a solid and can be fashioned into a spoon shape.  Being a silvery, metallic metal, it looks just like a silver teaspoon. However, if you were to stir your cup of hot tea or hot coffee with the gallium spoon, the spoon will melt because the temperature of the tea or coffee will be above the melting point of the gallium.



Further Reading
History of the Periodic Table
Periodic Table of the Elements
Metals and Non-metals
Chemical and Physical Changes
Writing Ionic Formula
Naming Ionic Compounds
Temperature Conversions
Latent Heat

Suggested Study Questions

1. Use the Periodic Table to find the following for gallium:
   • symbol
   • atomic number
   • atomic mass
2. With reference to the Periodic Table explain why Mendeleev would have named the unknown element, located where gallium is now known to be, ekkaaluminium.
3. Gallium often occurs in compounds in the +3 oxidation state, or as an ion in salts with a charge of 3+. Give the most likely formula for each of the following:
   • gallium chloride
   • gallium oxide
   • gallium hydroxide
4. Give the most likely name for each of the following:
   • GaH₃
   • Ga(NO₃)₃
   • Ga₂(CO₃)₃
5. Does the video show a chemical or a physical process? Explain your answer.
6. Sketch a temperature vs time curve to describe the melting of gallium.
7. Convert the melting point and boiling point of gallium from centigrade to kelvin.
8. Mercury has a melting point of about 234K and a boiling point of around 630K. Convert these temperatures to ^oC
9. Explain why mercury is a liquid at room temperature and pressure.
10. Could you freeze mercury by walking into an air-conditioned room like you can gallium? Explain your answer.

Skutterudites and Thermoelectric Generators

More than 60 percent of the energy produced by cars, machines, and industry around the world is lost as waste heat. If we could use this wasted energy we could improve the efficiency with which we use fuels, and benefit the environment.

Thermoelectric generators are devices which convert heat energy directly into electrical energy. Semi-conducting bismuth telluride, Bi₂Te₃, can be used to convert heat into electrical energy, but it is only about 5% efficient, too low to be useful in practical thermoelectric generators.
A number of scientists have been working with skutterudites to see if they can be used to increase the efficiency of thermoelectric generators.
Skutterudites have the general formula MX₃ in which M can be cobalt, rhodium or iridium, and X can be phosphorus, arsenic or antimony. The most promising of these compounds have been the CoSb₃. These compounds have 32 atoms in the unit cell and can be represented with the Co atoms occupying the corners of cubes.
The thermal conductivity of CoSb3 is too high for them to be used effectively.

So scientists have tried adding fillers to the structure to reduce the thermal conductivity. Rare earth elements and alkaline earth metals have been used as fillers.

Until recently these compounds have taken many days to make and have been expensive to produce. Oregan State University scientists have found a way to use microwaves to turn powdered metals into skutterudites in a few minutes and at a much lower cost. The first compound they produced using this technique was an indium cobalt antimonite compound in which indium is the filler.

Reference
Krishnendu Biswas, Sean Muir, M. A. Subramanian. Rapid Microwave Synthesis of Indium Filled Skutterudites: An energy efficient route to high performance thermoelectric materials. Materials Research Bulletin, 2011; DOI: 10.1016/j.materresbull.2011.08.058

Further Reading
Periodic Table
Writing Ionic Formula
Naming Ionic Compounds

Suggested Study Questions

1. Complete the following sentences:
   • A thermoelectric generator converts heat energy into ? energy.
   • A battery converts ? energy into electrical energy.
   • In a torch, the ? energy in the battery is converted into ? energy when the torch is turned on.
     
   • The ? energy in petrol (gasoline) is converted into ? energy when the fuel is combusted.
   • The ? energy released during combustion of a fuel can be converted into ? energy to move a car forward.
2. Skutterudites have the general formula MX₃. Write the formula of the skutterudite formed in each of the following situations:
   • M = cobalt and X = antimony
   • M = rhodium and X = phosphorus
   • M = iridium and X = arsenic
3. Give the name for each of the compounds formed in question 2.
4. For each of the following pairs of atoms, determine which is the most electronegative:
   • cobalt and antimony
   • rhodium and phosphorus
   • iridium and arsenic
5. Locate the elements cobalt, rhodium and iridium in the Periodic Table. In what ways do you expect these elements to be similar? Explain your answer.
6. Locate the elements phosphorus, arsenic and antimony in the Periodic Table. In what ways do you expect these elements to be similar? Explain your answer.
7. Give the names and chemical symbols of four examples of rare earth elements.
8. Give the names and chemical symbols of four examples of alkaline earth metals.
9. Write a possible formula for the skutterudite indium cobalt antimonite.
10. One structure has been represented as In_xCe_yCo₄Sb₁₂. Explain why this is an example of a skutterudite.
    
    
    
    

Heavy Metal Pollution

Hard water contains calcium and magnesium cations which can be removed using a suitable ion exchange resin.
Heavy metal ions such as cadmium, copper, chromium, mercury, nickel, lead and zinc, may also be present in water at unacceptable levels. This is referred to as heavy metal pollution of water.
Run off from roads is a large source of heavy metal contamination in water:

• Lead: leaded petrol (gasoline), tire wear, lubricating oil and grease, bearing wear
• Zinc: tire wear, motor oil, grease, brake emissions, corrosion of galvanized parts
• Iron: car body rust, engine parts
• Copper: bearing wear, engine parts, brake emissions
• Cadmium: tire wear, fuel burning, batteries
• Chromium: air conditioning coolants, engine parts, brake emissions
• Nickel: diesel fuel and petrol (gasoline), lubricating oil, brake emissions

Many of these heavy metals form negatively charged complex ions in water.
For example, chromium can form the chromate ion, CrO₄²⁻, and the dichromate ion, Cr₂O₇^2-.
Existing water treatment processes to remove these negatively charged ions can be inefficient and expensive.

Chemists at the University of California, Santa Cruz, have now developed a new type of material that can soak up negatively-charged pollutants from water. The new material called SLUG-26 contains copper hydroxide ethanedisulfonate.

Copper hydroxide ethanedisulfonate has a layered structure of positively-charged two-dimensional sheets with a high capacity for holding onto negative ions. These positively charged sheets are made up of [Cu4(OH)6]2+ ions as shown to the right. Copper atoms are shown in green and oxygen atoms are shown in red. The ethanedisulfonate exists as a counteranion.

This material could be used to treat polluted water through an ion exchange process similar to water softening. SLUG-26 provides a positively-charged substrate that can exchange a nontoxic negative ion for the negatively-charged pollutants.
The researchers are currently focusing on the use of SLUG-26 to trap the radioactive metal technetium, which is a major concern for long-term disposal of radioactive waste. Technetium is produced in nuclear reactors and has a long half-life of 212,000 years. It forms the negative ion pertechnetate in water and can leach out of solid waste, making groundwater contamination a serious concern.

Reference
Honghan Fei, Scott R. J. Oliver. Copper Hydroxide Ethanedisulfonate: A Cationic Inorganic Layered Material for High-Capacity Anion Exchange. Angewandte Chemie, 2011; DOI: 10.1002/ange.201104200

Further Reading
Periodic Table
Oxidation States
Zeolites

Suggested Study Questions

1. Give the chemical symbol for each of the following elements:
   • calcium
   • magnesium
   • cadmium
   • copper
   • chromium
   • mercury
   • nickel
   • lead
   • zinc
   • technetium
2. Identify which group of the periodic table each of the metals above belongs to.
3. Give the oxidation state for the metal atom in each of the following compounds:
   • CrO₄²⁻
   • Cr₂O₇^2-
   • [Cu₄(OH)₆]²⁺
4. Zeolites can be used to soften hard water. Write an equation to describe the process in which calcium ions in hard water are exchanged for sodium ions.
5. Suggest some possible non-toxic anions that could be exchanged for the toxic pertechnetate anion using SLUG-26.
6. Write an equation to show how the pertechnetate anion could be exchanged for one of the non-toxic anions in question 5.
7. Describe some other possible uses, apart from the removal of pertechnetate anions, for SLUG-26.
   
   
   

Molecular Motor

The Guinness World Record for the smallest electric motor currently stands at 200 nanometers, a human hair is about 300 times wider! Now Chemists at Tufts University's School of Arts and Sciences say they have developed the world's first single molecule electric motor, just 1 nanometer in diameter.

The molecular motor was produced when a butyl methyl sulfide molecule had been placed on a conductive copper surface and given an electrical charge. This sulfur-containing molecule had carbon and hydrogen atoms radiating off to form what looked like two arms, with four carbons on one side and one on the other. These carbon chains were free to rotate around the sulfur-copper bond.

The team determined that by controlling the temperature of the molecule they could directly impact the rotation of the molecule. Temperatures around 5 K, or about -450ºF, proved to be the ideal to track the motor's motion. The motor spins much faster at higher temperatures

Reference
Heather L. Tierney, Colin J. Murphy, April D. Jewell, Ashleigh E. Baber, Erin V. Iski, Harout Y. Khodaverdian, Allister F. McGuire, Nikolai Klebanov, E. Charles H. Sykes. Experimental demonstration of a single-molecule electric motor. Nature Nanotechnology, 2011; DOI: 10.1038/NNANO.2011.142

Further Reading
SI Unit Conversions
Temperature Conversions
Nomenclature
Molecule Polarity
Intermolecular Forces
Molecular Mass (formula weight) Calculations
Percentage Composition
Empirical and Molecular Formula

Study Questions:

1. Convert 200 nanometers to a diameter in
   • meters
   • micrometers
   • millmeters
   • decimeters
2. Form the information in the article above:
   • What is the diameter of a human hair in nanometers?
   • What is the size ratio of the molecular motor to a human hair?
3. Convert the following temperatures:
   • 5K to ^oC
   • 0K to ^oC
   • 100^oC to K
   • 25^oC to K
     
4. On the molecular structure of butyl methyl sulfide:
   • identify the butyl group
   • identify the methyl group
5. For a molecule of butyl methyl sulfide:
   • write the molecular formula
   • give the empirical formula
     
   • calculate the molecular mass
   • calculate the percentage composition
     
   
   
6. Is butyl methyl sulfide a polar or non-polar molecule? Explain your answer.
7. Do you expect butyl methyl sulfide to be water soluble? Explain your answer.
   
   
   
   

Diamond Planet Discovered

Scientists from Australia, Germany, Italy, the UK and the USA, have detected a companion planet for Pulsar J1719-1438 in our Milky Way, and they believe that this companion planet could be made of diamond. The planet is thought to be small, less than 60,000km in diameter, with a mass slightly greater than that of Jupiter, about 2 x 10²⁷kg.
P1719-1438 and its planet are so close together that the planet is most likely to be a 'stripped-down' white dwarf, that is, one that has lost its outer layers and over 99.9% of its original mass. Based on the planet's orbiting times, the scientists think that this remnant is likely to be made up mostly of carbon and oxygen, while its high density suggests that the material present is crystalline, which leads them to believe that the planet could contain a sizable proportion of diamond.

Graphite can be transformed into diamond under pressures of more than about 4GPa, as is shown in the simplified phase diagram on the right. On Earth, diamonds can be formed in the mantle where the pressure is great enough to transform carbon sources into diamonds. Diamonds can also form when a meteorite impacts on the Earth because the impact creates a zone of high pressure and temperature in which carbon can be transformed into diamond.

Reference
M. Bailes, S. D. Bates, V. Bhalerao, N. D. R. Bhat, M. Burgay, S. Burke-Spolaor, N. D'Amico, S. Johnston, M. J. Keith, M. Kramer, S. R. Kulkarni, L. Levin, A. G. Lyne, S. Milia, A. Possenti, L. Spitler, B. Stappers, W. van Straten. Transformation of a Star into a Planet in a Millisecond Pulsar Binary. Science, 2011; DOI: 10.1126/science.1208890

Further Reading
Mass Conversions
Density Calculations
Allotropes

Study Questions

1. Convert 60,000km to a distance in:
   • meters
   • centimeters
     
   • millimeters
     
2. Convert 2 x 10²⁷kg to a mass in
   • grams
   • megagrams
   • gigagrams
     
3. What is the approximate radius of of the planet in cm?
4. What is the volume of the planet in cm³ (assuming the planet is spherical)?
5. Calculate the approximate density of the newly discovered planet (in g/cm³).
6. Convert 4GPa to a pressure in:
   • kilopascals
   • pascals
   • megapascals
   • atmospheres
     
   
   
7. Using the phase diagram for carbon in the article above:
   • What is the minimum temperature and pressure required to produce liquid carbon from gaseous carbon?
   • What is the maximum pressure at which graphite can exist?
   • What is the maximum temperature at which graphite can exist?
     
   • How many phases of carbon are present at 4500K and 0.01GPa?
   • What is the triple point for diamond?
     
   
   

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

Rhodium

Rhodium, symbol Rh, is the rarest of all non-radioactive metals on Earth, and therefore an expensive metal. On the 22nd July 2011, 1 gram of rhodium cost $(AUD)38 compared to 1 gram of gold which cost $(AUD)31 or 1g of silver for only 78 cents !
Rhodium is a transition metal with a density of 12.41 gcm^-3 and is found in nature as the free metal, or alloyed with similar metals such as platinum or nickel, but not as a chemical compound.
Naturally occurring rhodium is composed of only one isotope, rhodium-103.
Only about 3 tonnes of rhodium are produced in the world each year, and most of this is used for catalyzing chemical reactions.
Approximately 80% of the rhodium produced is used as a reduction catalyst in the three-way catalytic converters of cars.
In a three-way catalytic converter three processes occur simultaneously:

1. Reduction of nitrogen oxides to nitrogen and oxygen: 2NO_x → xO₂ + N₂
2. Oxidation of carbon monoxide to carbon dioxide: 2CO + O₂ → 2CO₂
3. Oxidation of unburnt hydrocarbons (HC) to carbon dioxide and water

Other uses of rhodium include :

• plating white gold to make it appear more silvery (white gold is actually an alloy of gold with atleast one other metal such as nickel, manganese, palladium)
• plating sterling silver to make it appear more silvery (sterling silver is an alloy of silver containing 92.5% by mass silver and 7.5% by mass of other metals such as copper)

Queen's University chemists have just discovered that rhodium that is modified using carbon, nitrogen or hydrogen-based complexes changes colour to yellow in the presence of nitrogen, deep blue in the presence of oxygen, and brown in the presence of carbon monoxide. Modified metals, such as modified rhodium, that change colour in the presence of particular gases could warn consumers if packaged food has been exposed to air or if there's a carbon monoxide leak at home. This finding could potentially influence the production of both industrial and commercial air quality sensors.

Reference
Queen's University (2011, July 21). Modified metals change color in the presence of particular gases. ScienceDaily. Retrieved July 23, 2011, from http://www.sciencedaily.com­ /releases/2011/07/110721131159.htm

Further Reading
Periodic Table
Definitions of a Mole
Mass-Mole Calculations
Density
Isotopes
Relative Atomic Mass
Metals & Non-metals
Percentage Composition

Study Questions

1. Locate rhodium in the Periodic Table and give its
   • atomic number
   • relative atomic mass
2. Using the prices per gram of metal given in the story above, calculate
   • the price of the 3 tonnes of rhodium produced in the world each year
     
   • the price of 1 mole of rhodium
   • the price of 10 cubic centimeters of rhodium
   • the mass of $57,000 worth of rhodium
   • the volume of $57,000 worth of rhodium
3. Naturally occurring rhodium has only 1 isotope, rhodium-103. For this isotope give:
   • the number of protons in the nucleus of a rhodium atom
   • the number of neutrons in the nucleus of a rhodium atom
   • the mass number of this isotope of rhodium
   • the atomic number for this isotope of rhodium
4. If naturally occurring rhodium only has 1 isotope why is its relative atomic mass 102.9?
5. List the physical properties you would expect rhodium to have based on its position within the Periodic Table.
6. Why would coating white gold in rhodium make it appear more silvery?
7. A 25 kg sample of sterling silver contains only silver and copper.
   • What mass of silver is present in the sample?
   • What mass of copper is present in the sample?
8. A sample of white gold is found to contain only 1.39 g gold and 0.09g of nickel. Calculate the percent by mass of each element present in the sample.
   
   
   
   
   

Sepiolite

Sepiolite has been known since Roman times when it was used to filter and purify wine. No other mineral is known to absorb more water or other liquids as efficiently as sepiolite, which is why sepiolite is commonly used in cat litter. Sepiolite is also used to absorb liquid spillages, such as in oil spills, and odours and stabilise aqueous products like paints, resins and inks.
Sepiolite is an aluminosilicate clay mineral with a typical formula of Mg₄Si₆O₁₅(OH)₂·6H₂O.

Sepiolites absorb moisture by using tiny tunnels in the crystals. The elongated, needle-shaped sepiolite crystals pack very loosely into a lightweight porous material. The surface area ranges between 75 and 400 m²/g, meaning that 20g of mineral have an internal surface equivalent to that of a football court. This is why sepiolite can absorb 2.5 times its weight in water. The tunnels in the crystal structure along with the empty space between the needles form a capillary network through which liquids can easily flow deep inside the bulk where the molecules attach to the surface of the crystals.

A team of scientists from Spain and France has obtained, for the first time, single-crystal X-ray diffraction images of sepiolite, opening the path to industrial synthesis and further improvement of its properties. In synthetic form, sepiolite could bind food products and stabilise drugs, extending their shelf life and making sepiolite an edible product.

Reference
Manuel Sanchez del Rio, Emilia Garcia-Romero, Mercedes Suarez, Ivan da Silva, Luis Fuentes Montero, and Gema Martinez-Criado. Variability in sepiolite: Diffraction studies. American Mineralogist, 2011 DOI: 10.2138/am.2011.3761

Further Reading
Percentage Composition
Balancing Chemical Equations


Study Questions

1. Calculate the percentage composition of sepiolite, Mg₄Si₆O₁₅(OH)₂·6H₂O
2. Explain what the ·6H₂O part of the formula refers to.
3. Write a balanced chemical equation for the dehydration of hydrated sepiolite to form anhydrous sepiolite.
4. Calculate the maximum mass of water you could obtain from 1kg of hydrated sepiolite.
5. If the sepiolite in question 2 has a surface area of 200m²/g, what is the total surface area of the sample in question 4?
   
6. Use the equation in question 3 to explain why sepiolite is used in cat litter.
7. Sepiolite is an aluminosilicate mineral. Explain what is meant by the term aluminosilicate.
8. Sepiolite is sometimes referred to as a zeolite-like mineral. In what ways is sepiolite similar to a zeolite mineral?
   

Yellow Paint Pigments

Vincent van Gogh used a pigment known as chrome yellow to achieve the intensity of colour present in such famous 19^th century works of art as his Sunflowers paintings. Chrome yellow is made up of lead (II) chromate, PbCrO_4, and can be produced by mixing solutions of lead (II) nitrate and potassium chromate, then filtering off the lead (II) chromate precipitate.

Unfortunately, chrome yellow paint darkens in the presence of sunlight as Cr(VI) changes to Cr(III). The Cr(III) compounds form as a nanometer-thin coating over the pigment particles that make up the paint.

Because chrome yellow darkens in the presence of sunlight, and because it contains toxic lead, it was replaced with cadmium yellow by the 1950s. Cadmium yellow is actually cadmium sulfide. While cadmium yellow does not tend to change colour in sunlight, it does contain toxic cadmium.

Cadmium pigments are slowly being replaced by azo dyes which are of the general formula R-N=N-R', where R usually contains a benzene ring within its structure .

Reference
Letizia Monico, Geert Van der Snickt, Koen Janssens, Wout De Nolf, Costanza Miliani, Joris Dik, Marie Radepont, Ella Hendriks, Muriel Geldof, Marine Cotte. Degradation Process of Lead Chromate in Paintings by Vincent van Gogh Studied by Means of Synchrotron X-ray Spectromicroscopy and Related Methods. 2. Original Paint Layer Samples. Analytical Chemistry, 2011; 83 (4): 1224 DOI: 10.1021/ac1025122

Further Reading
Naming ionic compounds
Writing the formula of ionic compounds
Writing precipitation reaction equations
Oxidation numbers (states)
Oxidation and Reduction

Study Questions

1. For the compound PbCrO4 give the oxidation number (state) for:
   
• Pb
• Cr
• O
2. Write the formula for:
   
• lead (II) nitrate
• potassium chromate
• cadmium sulfide
3. For the compound potassium chromate, give the oxidation number (state) for:
   • K
   • Cr
   • O
   
   
4. For the reaction between lead (II) nitrate and potassium chromate, write the balanced
   
• molecular equation
• ionic equation
• net ionic equation
5. Name the spectator ions present in the reaction between lead (II) nitrate and potassium chromate.
   
6. Write an electron transfer equation to represent the reaction in which Cr(VI) changes to Cr(III) in the presence of sunlight.
7. For the equation above is:
   • Cr(IV) being oxidized or reduced?
   • Cr(IV) an oxidant or a reductant?
   • Cr(IV) an oxidizing agent or a reducing agent?
   
   

Nanoparticles in Sunscreens

Titanium dioxide and zinc oxide are currently used for sunscreens because they absorb and scatter light. University of Tennessee, Knoxville, scientists have found that nanoparticles found in ivy may protect skin from UV radiation at least four times better.

A yellowish material is secreted by the ivy to aid it in clinging to surfaces. Nanoparticles within this material create the ability for the vine leaves to hold almost 2 million more times than its weight as well as provide the ability to absorb and disperse light due to their large surface-to-volume ratio. Sunscreens made with ivy nanoparticles would probably not need to be re-applied after swimming because the nanoparticles are more adhesive, and, while metal-based sunscreens give the skin a white tinge, the ivy nanoparticles are virtually invisible.

The study indicates that ivy nanoparticles are less toxic to mammalian cells than small-scale metal oxides, have a limited potential to penetrate through human skin, and are easily biodegradable.

Reference:
University of Tennessee at Knoxville (2010, July 19). Nanoparticles in English ivy may hold the key to making sunscreen safer and more effective. ScienceDaily. Retrieved July 22, 2010, from http://www.sciencedaily.com­ /releases/2010/07/100719162955.htm

Study Questions

1. Write the formula for titanium dioxide and for zinc oxide.
2. Give the oxidation state (number) for titanium and zinc in the compounds above.
3. What is a nanoparticle?
4. Explain the term surface-to-volume ratio.
5. Why do nanoparticles have a large surface-to-volume ratio?
6. How is the scattering of light affected by differences in surface-to-volume ratio?
7. Why are titanium dioxide and zinc oxide the preferred metal oxides for use in sunscreens?
   

Topological Insulators

In an electrical conductor, negatively charged electrons can hop between atoms and move freely in their interior or on the surface. These free electrons are responsible for the generation of electric current. For most metals, electrons in the interior carry most of the current, while surface electrons are only weakly mobile. Some materials, such as glass, have structures that impede electron flow and are called insulators.

A topological insulator is a substance that acts as an insulator in its interior while permitting the movement of charges on its boundary. This can occur when a perpendicular magnetic field is applied, this is known as the quantum Hall effect.
Princeton scientists have discovered a new type of typological insulator, an antimony crystal, which does not require the application of a magnetic field.

Reference:
Jungpil Seo, Pedram Roushan, Haim Beidenkopf, Y. S. Hor, R. J. Cava, Ali Yazdani. Transmission of topological surface states through surface barriers. Nature, 2010; 466 (7304): 343 DOI: 10.1038/nature09189

Study Questions

1. What is required in order for a material to be considered an electrical conductor.
2. Give three examples of good electrical conductors.
3. Give three examples of electrical insulators.
4. In general, what type of substances conduct electricity?
5. In general, what type of substances do not conduct electricity?
6. If electrons are negatively charged, why are atoms considered to be neutral?
7. Why do you think electrons are more free to move within the interior of a material compared to its surface?
   

Gold Nanoparticle Dispersion

Queensland University of Technology (QUT) scientists have developed a new technique for dispersing metals in nanoparticle form throughout polymers or plastic materials.

The properties of metals change when they are in nano form. When nanoparticles are added to plastics, a new range of composite materials are formed.

When gold nanoparticles are added to paint, essentially a plastic, the intensity of colours and durability are increased.

Mixing gold nanoparticles with titanium dioxide, TiO₂, using a plastic mould makes a very efficient catalyst for water purification as the titania absorbs light, converting it into electricity which is then passed into the conductive gold.

Queensland University of Technology (2010, May 6). Gold nanoparticles promise to enrich everyday products. ScienceDaily. Retrieved May 8, 2010, from http://www.sciencedaily.com­ /releases/2010/05/100505092004.htm

Scientists See in the Dark

Conventional night vision goggles use a photocathode, a cathode ray tube-like vacuum tube made of thick glass, to convert infrared light photons into electrons which are then accelerated under high voltage and driven into a phosphorous screen producing greenish images of objects invisible to the naked eye in the darkness.

University of Florida scientists have produced an imaging device that replaces the photocathode with several layers of organic semiconductor thin film materials. The photodetector is connected in series with an LED. Infrared light photons are converted into electrons in the photodetector which are then injected into the LED which generates visible light. This imaging device would be light-weight and inexpensive to produce since it could be made using the same equipment currently used to produce laptop screens and flat-screen TVs. This new night-vision technology could be used on mobile phones, car windshields, even standard glasses.

Do Young Kim, Dong Woo Song, Neetu Chopra, Pieter De Somer, Franky So. Organic Infrared Upconversion Device. Advanced Materials, 2010; DOI: 10.1002/adma.200903312