Mass Concentration (m/v)

 There are lots of ways to measure concentration in chemistry.

One method is to divide the mass of solute by the volume of solution: m/v

This is called a mass concentration and common units for mass concentration are g/L or g L^-1

AUS-e-TUTE has just added new teaching and learning resources for mass concentration calculations (game, test, drill, quiz, worksheet and problem solving template).

Members should log-in to use these new resources.

Non-members can go to the "free-to-view" tutorial at https://www.ausetute.com.au/massconc.html

Chemistry of Tooth Decay and Prevention

Tooth decay is a major health concern.

For more than 50 years we have been adding fluoride to our water supplies and toothpaste to help prevent tooth decay.

It is estimated that this fluoridation of drinking water alone has resulted in a 25% decrease of tooth decay in children and adults.

What causes tooth decay and how does fluoride prevent tooth decay and cavities?

 Learn about the chemistry of tooth decay and how to prevent it in the March 2021 issue of AUS-e-NEWS. Subscribe to AUS-e-NEWS for free at https://www.ausetute.com.au/ausenews.html

What is the pH of a Strong Base After You Dilute It?

The problem with strong bases like sodium hydroxide and potassium hydroxide are that they absorb moisture from the air making it difficult to accurately weigh them. So we rely heavily on obtaining an accurately known concentration for an aqueous solution of a strong base (using titration techniques for example) and then diluting this stock solution to produce new, dilute solutions of known concentration and pH.
When you dilute an aqueous solution of a strong base :

• hydroxide ion concentration decreases (towards 10^-7 M)
• pOH increases (towards 7)
• hydrogen ion concentration increases (towards 10^-7 M)
• pH decreases (towards 7)

Visit AUS-e-TUTE's new tutorial to understand why, then log-in to the Members ONLY area to play the game, answer test and exam questions (which give you instant feedback), take the quiz, or, just for teachers, you could make a printable worksheet or quiz.

Alloys

What is an alloy?
What kinds of alloys are there?
Are steel, brass and bronze alloys?
How do the properties of an alloy differ from the properties of the elements making up the alloy?

Sounds like you need to refer to AUS-e-TUTE's new Binary Alloy resources!
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/alloys.html

Want to know what you're missing out on if you're not an AUS-e-TUTE Member?
Go to http://www.ausetute.com.au/membership.html

Ready to start improving your chemistry exam results?
Then it's time to join AUS-e-TUTE: http://www.ausetute.com.au/register.html

Coral Reef Dissolution

Coral reefs dominate much of the world's tropical coastline, covering about 15% of the seabed shallower than 30 metres.

The largest coral reef in the world is the Great Barrier Reef off the north-east coast of Australia.

What impact will increasing amounts of atmospheric carbon dioxide have on our coral reefs?

Find out in this edition of AUS-e-NEWS!

If you haven't received your copy of AUS-e-NEWS, or if you would like to subscribe to our free quarterly newsletter, AUS-e-NEWS, the email us at

 

Effect of Temperature on Solubility

What happens to the solubility of a salt or a gas at constant pressure when the temperature of the solution changes?
This can be treated as just a special case of Le Chatelier's Principle .....

And AUS-e-TUTe has just added new resources to help you understand the effect of temperature on solubility.
AUS-e-TUTE Members should log-in to use the new tutorial (includes a drill), game, test and exam.

If you are not an AUS-e-TUTE member, there is non-interactive "free-to-view" tutorial currently available for evaluation purposes at http://www.ausetute.com.au/solubilitylcp.html


Get a better understanding of concepts in chemistry, and improve your problem solving ..... join AUS-e-TUTE today!

Solutes, Solvents and Solutions

Seems like the science of solutions is simply seething with "s" sounds:

• solute
• solvent
• solution
• solubility
• solvation
• saturated (and unsaturated)

 but what do they mean?

AUS-e-TUTE has just added new resources to help you find out, and, understand the differences!
AUS-e-TUTE Members should log-in to use these new "Solutions Concepts" resources.

Not an AUS-e-TUTE Member?
A free-to-view tutorial is currently available on this topic for evaluation purposes at http://www.ausetute.com.au/solutions.html

When you're serious about learning some chemistry, join us at www.ausetute.com.au

Heat of Solution

Have you ever wondered why some salts dissolve in water to release heat while others absorb energy?

If so, you should take a look at AUS-e-TUTE's new resources on the Molar Enthalpy of Solution (or Molar Heat of Solution).

AUS-e-TUTE members should log-in to view the new tutorial, game, test, exam and homework checker under the heading Thermochemistry, and the topic heading Heat (enthalpy) of Solution.

Not an AUS-e-TUTE Member?
Currently there is a "free-to-view" tutorial available for evaluation purposes at http://www.ausetute.com.au/heatsolution.html

Find out about the benefits of AUS-e-TUTE membership at
http://www.ausetute.com.au/membership.html

then, when you are ready to start improving your chemistry results, you can join AUS-e-TUTE at
http://www.ausetute.com.au/register.html

Henry's Law and the Solubility of Gases

What is the relationship between the solubility of a gas in a solvent, and the pressure of the gas?
What happens to the solubility of gases as the temperature changes?
If you are asking these questions, you need AUS-e-TUTE's new Henry's Law resources!

AUS-e-TUTE Members will find the new resources listed under Gas Laws in the Members Only Test Centre. Where relevant to your syllabus, links to these resources have also been added to your Syllabus Study Guide.

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

Then, when you are ready to start improving your chemistry results, you can join AUS-e-TUTE at
http://www.ausetute.com.au/register.html

Dilution Factors

I've always thought that an understanding of dilution factors can make a Chemistry student's life a whole lot easier, but at the same time, always avoided teaching it (or indeed making reference to it) because of the muddle students make of it (thinking that every calculation involving a solution can be dealt with using dilution factor "formulae") .... and even worse, biology students always seem to have a desire to just "add volumes" together (even if the volumes are not additive!).

The new dilution factor resources are available to AUS-e-TUTE Members in the Members Only area (and teachers will find a worksheet wizard in the Teachers Area).

Not a member?
You can find out about AUS-e-TUTE Membership at  http://www.ausetute.com.au/membership.html

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

There is a free-to-view tutorial currently available at http://ausetute.com.au/dfactor.html

Drunken Fruit Flies

Wasps are a major killer of fruit flies. They inject their eggs inside fruit fly larvae, then, when the wasp egg hatches, the wasp larva starts eating the fruit fly lava from the inside!
Scientists at Emory University have found that fruit flies prefer to lay their eggs in an environment  with a "high" concentration of ethanol. The fruit flies have evolved a certain amount of tolerance to this toxic ethanol, but the wasps who inject their eggs inside fruit fly larvae find the ethanol level to be lethal. Furthermore, fruit fly lava that have been infected with wasp larva tend to prefer to eat food with a high ethanol content, this raises their blood alcohol level and helps kill the wasp larva.

The most common natural source of ethanol is rotting fruit. Yeasts on rotting fruit can ferment the fruit sugars, like fructose, to produce ethanol:

C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂

This fermentation reaction takes place in anaerobic environments, that is, environments in which oxygen is not present.
The concentration of ethanol in rotting fruits has been  found to be between 0.04 and 0.72 v/v%. By comparison, the ethanol content in beer is usually between 3 and 6 v/v%, while the ethanol content of wine is between 8 and 11 v/v%.
Volume/volume (or volume) percent is a common way to refer to the concentration of alcoholic solutions. It refers to the volume of solute divided by the volume of solution which is then multiplied by 100, that is:

v/v% = V(solute)/V(solution) x 100

Beer that is 3 v/v% ethanol contains 3 mL of ethanol in every 100 mL of beer.

Wine that is 11 v/v% ethanol contains 11 mL of ethanol in every 100 mL of wine.

This preference for eating rotting fruit containing ethanol displayed by the fruit flies seems to be uncommon. Most animals, including humans, seem to prefer ripe, but not rotting, fruit.

References:

1. B. Z. Kacsoh, Z. R. Lynch, N. T. Mortimer, T. A. Schlenke. Fruit Flies Medicate Offspring After Seeing Parasites. Science, 2013; 339 (6122): 947 DOI: 10.1126/science.1229625
2. Neil F. Milan, Balint Z. Kacsoh, Todd A. Schlenke. Alcohol Consumption as Self-Medication against Blood-Borne Parasites in the Fruit Fly. Current Biology, 2012; 22 (6): 488 DOI: 10.1016/j.cub.2012.01.045

Further Reading:
Fermentation
Carbohydrates
Naming Alcohols
Density

Suggested Study Questions:

1. Calculate the volume of ethanol in a stubby (375 mL) of full strength beer (ethanol concentration 4.8 v/v%).
2. An average standard wine glass has a volume of 150 mL. What volume of ethanol is present in a standard wine glass of white wine with an ethanol concentration of 11.5 v/v%?
3. Port is an example of a fortified wine, that is, a wine that has had an additional distilled beverage like brandy added to it to increase its alcohol content to about 17.5 v/v%. A standard port glass has  a volume of 60 mL. Calculate the volume of ethanol in a standard glass of port.
4. The specific gravity (density) of ethanol is 0.789 g/mL. Calculate the mass of ethanol present in a stubby (375 mL) of
   • full strength beer (5 v/v% ethanol)
   • light beer (2.7 v/v% ethanol)
5. Spirits such as rum and vodka, have an ethanol concentration of approximately 40 v/v%. A standard "nip" is 30 mL. Calculate:
   • the volume of ethanol in a nip of vodka
   • the mass of ethanol in a nip of vodka
6. The alcohol content of Marsala wine is increased by allowing water to evaporate off it. The concentration of ethanol in Marsala wine will reach about 18 v/v%. Calculate:
   • volume of ethanol in a 750 mL bottle of Marsala
   • mass of ethanol in this bottle of Marsala wine
7. A particular type of wine barrel holds 225 L of wine. Calculate the mass of ethanol present if the wine in the barrel is
   • red wine (13 v/v% ethanol)
   • white wine (11.5 v/v% ethanol)
   • champagne (12 v/v% ethanol)

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