Saturday, November 12, 2016

Fatty Acids

Do you want to answer any of the questions listed below:
  • What is a fatty acid?
  • What are the structures and formulae of common fatty acids?
  • What is a saturated fatty acid?
  • What is an unsaturated fatty acid?
  • What is a monounsaturated fatty acid?
  • What is a polyunsaturated fatty acid?
  • What determines the melting point and solubility of a fatty acid?
  • What is an essential fatty acid?
  • What is an omega-3 fatty acid?
  • What is an omega-6 fatty acid?
AUS-e-TUTE has new resources to help you answer these questions!
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If you are not an AUS-e-TUTE Member, a "free-to-view" Fatty Acids tutorial is currently available at http://www.ausetute.com.au/fattyacid.html for evaluation purposes.

Friday, October 21, 2016

Vitamins

Does it seem that dieticians and nutrition experts seem to make a huge fuss about eating foods that seem to contain infinitesimal amounts of those mysterious substances known as vitamins?
Well, there is some good, sound chemistry behind why this is so.
Find out about the chemistry of vitamins with AUS-e-TUTE's newest set of resources!

Members should log-in to access the Vitamins tutorial, game, test and exam.

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

Sunday, October 2, 2016

Gravimetric Analysis

Gravimetric analysis can be used to determine the quantity of an ion present in a solution.
This can be done by adding a reagent that causes the ion under investigation to form an insoluble compound (a precipitate) that precipitates out of the solution.
AUS-e-TUTE has "free-to-view" tutorials currently available on :
  1.  Determining the percentage by mass of sulfate in a lawn fertiliser
  2.  Determining the concentration of chloride ions in water
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  • games
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  • exams (with worked solutions)
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Saturday, September 10, 2016

Salt from Seawater



About 200 Mt of sodium chloride are consumed every year in the world.
Some sodium chloride will be added to food, some will be used as a highway de-icing agent in cold climates, but most of it will be used in industries such as leather tanning, dye manufacturing, paper production, and in the production of other chemicals such as sodium carbonate, sodium hydroxide and chlorine.
The largest source of sodium chloride is the world's oceans.
So, how hard can it be to produce sodium chloride?
Surely you just evaporate the water off seawater and "hey presto", sodium chloride!
In reality, it's not quite that simple .....

Learn more in the September 2016 edition of AUS-e-NEWS.

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typing "subscribe" as the subject.
 

Thursday, September 8, 2016

Coral Killing Sunscreens

More than a year ago, a study involving marine scientists from Virginia, Florida, Israel, the US National Aquarium and the US National Oceanic and Atmospheric Administration, identified a common chemical component of sunscreens capable of damaging coral reefs.
This chemical is commonly known as oxybenzone and its structure is shown below:
This molecule has the systematic IUPAC name of (2-hydroxy-4-methoxyphenyl)(phenyl)methanone
Notice how every carbon atom (except that of the terminal methyl group, the carbon atom of the methoxy group) is involved in a double bond?
This kind of arrangement leads to some interesting properties. One of these properties is that molecules like this one are good at absorbing UV light. So, oxybenzone is added to products such as plastics, sunscreens, hairsprays, nail varnish and cosmetics like lipstick and mascara, as a UV filter.
Sunscreen lotion can contain between 1 and 10% oxybenzone.
Unfortunately, oxybenzone enters the water when people wearing sunscreens or other cosmetics decide to go for a swim. Researchers estimate that between 6,000 and 14,000 tonnes of sunscreen lotion are emitted into the waters of coral reefs each year.
The same property that makes it ideal as a sunscreen makes it a catastrophe for our coral reefs! Blocking UV light to baby corals causes growth deformities, and worse, the coral becomes encased in its own skeleton and dies.
In 2016, a study of Hawaii's sea waters found the oxybenzone concentration ranged from 0.8 to 19.2 µg/L. A previous study found that oxybenzone concentrations as low as 0.062 µg/L could harm the coral.
Hawaii's government asked swimmers, surfers and divers to avoid using sunscreens that contain oxybenzone as a measure towards protecting their reef.

Reference:
Hawaii targets sunscreens with oxybenzone 

Suggested Study Questions:
  1. Draw a molecule of oxybenzone, and, locate and name each functional group
  2. Give the molecular formula for oxybenzone.
  3. Calculate the molar mass of oxybenzone.
  4. Draw the 2-dimensional structural formula for oxybenzone.
  5. Oxybenzone readily dissolves in ethanol. Explain how oxybenzone can dissolve in ethanol.
  6. Oxybenzone does not dissolve in water. Explain why oxybenzone dissolves in ethanol but not in water.
  7. Given the data in the article, calculate the mass of oxybenzone that could be emitted into coral reef waters each year.
  8. Convert the following concentrations of oxybenzone to concentrations in parts per million
    • 0.062 µg/L
    • 0.8 µg/L
    • 19.2 µg/L
  9. Convert the following concentrations of oxybenzone to concentrations in moles per litre (molarity)
    • 0.062 µg/L
    • 0.8 µg/L
    • 19.2 µg/L
  10. Assume a 375 g tube of sunscreen lotion contains 10% by mass oxybenzone. Use the data in the article to calculate an "average" number of tubes of sunscreen that washed into the ocean each year. Justify your answer.

Thursday, July 21, 2016

Titanium Gold Alloy

Titanium is the metal used to replace hip and knee joints because it is strong, resistant to wear, and, is nontoxic.

Before titanium was used to replace hips and knees, stainless steel was used.
The density of stainless steel used to make replacement hips and knees is about 7.8 g cm3. The density of titanium metal is 4.506 g cm3, about half the density of stainless steel. This means that a replacement joint made out of titanium will weigh less than the same replacement joint made out of stainless steel.
Titanium is also strong. The strength of the material used to replace hip and knee joints is important because you do not want your new joint to bend or break or under strain.

Titanium has a melting point of 1670°C and a boiling point of 3287°C, which means it remains solid over the range of temperatures humans are exposed to. This is important because you want your new hip or knee replacement to remain a solid!
Naturally occurring titanium is made up of a number of isotopes, all of which are stable so they do not undergo nuclear decay. This is important because it means that there is no loss of titanium mass due to radioactive decay, and there is no fear of damage to cells from the emission of radiation.
isotope atomic mass abundance
46Ti45.9538.25
47Ti46.9527.44
48Ti47.94873.72
49Ti48.9485.41
50Ti49.9455.18

Titanium metal will react with water, halogens and dilute hydrochloric acid, but only if the temperature is elevated well above body temperature. Similarly, titanium metal will react with oxygen in a combustion reaction at elevated temperatures. Titanium metal does not appear to react with bases at all. Therefore, titanium is unlikely to react with substances found in the human body.

Researchers at Rice University have found that alloying titanium with gold can produce an even better material to use for replacement hips and knees. Mixing titanium and gold in the ratio of 3:1 at high temperature produces an alloy that is 3 times harder than steel and 4 times harder than the pure titanium commonly in use for hip and knee replacements. The atoms of titanium and gold in this alloy are packed in a cubic arrangement, an arrangement that is usually associated hardness. The structure of this alloy is shown below:

This titanium gold alloy has been found to be even more biocompatible that pure titanium.
The researchers intend to undertake further studies to investigate whether using chemical dopants might improve the alloy's hardness even further.

Reference:
Rice University. "Titanium and gold equals new gold standard for artificial joints: Titanium-gold alloy that is 4 times harder than most steels." ScienceDaily. ScienceDaily, 20 July 2016. 

Further Reading
Metals and Non-metals 
Density
Isotopes
Relative Atomic Mass
Alloys

Suggested Study Questions

  1. Titanium and gold are both metallic metallic elements.
    • What are the physical properties common to most metallic elements?
    • What are the chemical properties common to most metallic elements?
  2. Draw up a table of the physical properties of titanium.
  3. A typical knee replacement made out of titanium has a mass of 560 g.
    • Calculate the volume of the titanium knee replacement.
    • Calculate the mass of the same knee replacement if it were made out of stainless steel
  4. Define the term isotope.
  5. Determine the number of protons in the nucleus of an atom of each of the isotopes of titanium listed in the article above.
  6. Determine the number of neutrons in the nucleus of an atom of each of the isotopes of titanium lists in the article above.
  7. Which is the most abundant isotope of titanium? Explain your answer.
  8. Use the data in the article above to calculate the relative atomic mass of naturally occurring titanium.
  9. Given the atomic radius of titanium is  176 pm (1.76 x 10-10 m) and the atomic radius of gold is 174 pm (1.74 x 10-10 m), do you think the alloy of titanium and gold discussed in the article above is an interstitial alloy or a substitutional alloy? Explain your answer.
  10. Consider the structure of the titanium gold alloy shown in the diagram in the article above.
    • The blue balls represent which atoms of which element?
    • The red balls represent which atoms of which element?

Sunday, July 10, 2016

Sticky Surfactant?

 How often have you found that, no matter how hard you try, it is impossible to get that last bit of detergent out of the plastic bottle? Do you turn the bottle upside down and wait, letting the cleaning stuff flow to the bottom, but then find there is still some left no matter how hard you squeeze the bottle? Do you then try adding a bit of water and shaking it so that you can extract just a little bit more of it out of the bottle? And then, do you eventually give up and finally chuck the bottle away, still containing a very small amount of the cleaning product?
Well, if you find this sticky surfactant problem unsatisfactory, you aren't alone!
 The reason why it is so hard to remove ALL the detergent from the bottle is the same reason why the detergent makes a good cleaning product, that is, surfactant molecules have a long non-polar chain that attracts other non-polar substances like oils and grease, and a polar or ionic head that attracts other polar substances like water. So, if you pour a detergent, containing surfactant molecules, into a non-polar plastic container like polyethylene or polypropylene, the non-polar parts of the surfactant molecule will be attracted to the non-polar surface of the bottle making it hard to get all the surfactant molecules out of the bottle.

But scientists at The Ohio State University have now developed a way to make the plastic bottles so that ALL your shampoo or "liquid" detergent will flow out of the bottle. It involves spray-coating the surface of the plastic with a solvent and ultrafine silica nanoparticles. The solvent softens the plastic enabling the silica to be embedded in the  surface formed "Y" shaped channels a few micrometers high and a few micrometers apart. The branches of the "Y" shapes overhang the plastic surface at an angle of less than 90 degrees resulting in trapped air. Surfactant molecules are then in contact with air rather than plastic so that they can form spherical beads that will roll off.

The university hopes to further develop this process and license the coating technique to manufacturers, not just for shampoo bottles, but for other plastic products that have to stay clean, such as biomedical devices or catheters.

Reference: 
Ohio State University. "Shampoo bottle that empties completely, every last drop." ScienceDaily. ScienceDaily, 27 June 2016.

Further Reading:
Soaps
Detergents
Wetting
Intermolecular Forces
Nanoparticles and Nanotechnology
Molecular Formula
2-Dimensional Structural Formula
Condensed (semi-structural) formula
Skeletal Formula
Introduction to Functional Groups
Carboxylic Acids


Suggested Study Questions

  1. A typical soap molecule, sodium stearate is shown below:
    • Draw the full 2-dimensional structural formula for this molecule
    • Write the condensed (semi-structural) formula for this molecule
    • Write the molecular formula for this molecule
  2. Draw the skeletal formula for potassium stearate:
    • draw a ring around the functional group
    • name the functional group
    • describe the non-polar part of the molecule
    • describe the polar part of the molecule
  3. Draw a structural formula for stearic acid.
  4. Write a chemical equation for the neutralisation of stearic acid using sodium hydroxide in aqueous solution.
  5. Describe how soap removes dirt during washing.
  6. Sodium dodecyl sulfate shown below is a common surfactant molecule found in detergents
    • Draw the full 2-dimensional structural formula for this molecule
    • Write the condensed (semi-structural) formula for this molecule
    • Write the molecular formula for this molecule
  7. Draw the skeletal formula for potassium dodecyl sulfate:
    • draw a ring around the functional group
    • name the functional group
    • describe the non-polar part of the molecule
    • describe the polar part of the molecule
  8. Explain why sodium dodecyl sulfate is classified as an anionic detergent.
  9. Compare molecules of sodium dodecyl sulfate and sodium stearate
    • Desribe any similarities between the two molecules
    • Describe any differences between the two molecules
    • Explain how both molecules can be used to remove dirt during washing
  10. Consider the problem of detergent sticking to the inside walls of the plastic bottle.
    • Describe the physical properties of the plastic bottle that enable this to happen
    • Use a diagram to help explain why the detergent molecules can "stick" to the plastic bottle
    • Use a diagram to explain why adding water to the not-quite-empty plastic bottle allows more of the detergent to be removed