Why Fish Don't Freeze

Ever wondered why fish don't freeze in polar oceans where the temperature of the water falls below 0^oC?
The September 2010 issue of AUS-e-NEWS takes a look at the chemistry behind this interesting question.
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Protonated Water Clusters

Water molecules are polar. This causes neighbouring water molecules to be attracted to each other, forming hydrogen-bonds that link them into chains or clusters. The evaporation of water requires relatively large amounts of energy in order to break the hydrogen-bond networks apart.

Protonated water clusters, which have protons bound to them, are important model systems for the study of proton hydration in aqueous solutions, the process that determines the acidity (pH) and electrical conductivity of water.

The smallest protonated water cluster is the hydronium cation consisting of a single water molecule with an associated proton.
The Zundel ion is another protonated water cluster and is formed when a single proton is shared by two water molecules.

Scientists have been using infrared spectroscopy to determine the bond strengths, geometrical structures and chemical properties of protonated water clusters. When molecules are irradiated with infrared light, they vibrate in ways that depend on the wavelength, the colour, of the light. The frequency of the resulting vibrations allows scientists to deduce the three-dimensional structure of the molecule and the strength of the bonds between its atoms.

Reference:

1. Marcel sBaer, Dominik Marx, Gerald Mathias. Theoretical Messenger Spectroscopy of Microsolvated Hydronium and Zundel Cations. Angewandte Chemie, 23 August 2010 DOI: 10.1002/anie.201001672
2. G. Mathias, D. Marx. Structures and spectral signatures of protonated water networks in bacteriorhodopsin. Proceedings of the National Academy of Sciences, 2007; 104 (17): 6980 DOI: 10.1073/pnas.0609229104

Study Questions

1. Draw the molecular structure of a water molecule.
2. Use the structure above to explain what is meant by water being a polar molecule.
3. Draw a diagram to show how a hydrogen-bond can be formed between two water molecules.
4. Write the molecular formula for the hydronium cation.
5. Give the structural formala for the hydronium ion.
6. Based on the description of the Zundel ion given above, write the molecular formula for the Zundel ion.
7. Give the structural formula for the Zundel ion.
8. Another protonated water cluster is the Eigen ion, H₉O₄⁺ . Give a possible structural formula for the Eigen ion.
   

Dry Water

Discovered in 1968, "dry water" consists of 95% water, yet it is a dry powder which resembles powdered sugar at room temperature and pressure. Each powder particle contains a water droplet surrounded by modified silica. The silica coating prevents the water droplets from combining and turning back into liquid water. The result is a fine powder that can slurp up gases which combine with the water molecules to form hydrates.

Dry water can absorb over three times as much carbon dioxide gas as ordinary uncombined water and silica in the same length of time. This ability to absorb large amounts of carbon dioxide gas as a hydrate could make it useful in helping to reduce global warming since carbon dioxide gas is a major contributor to global warming.

Dry water can also be used to store methane, a component of natural gas. This could provide a safer, more convenient way to store methane fuel for use in vehicles powered by natural gas.

Reference:
American Chemical Society (2010, August 25). 'Dry water' could make a big splash commercially. ScienceDaily. Retrieved August 26, 2010, from http://www.sciencedaily.com­ /releases/2010/08/100825174102.htm

Study Questions

1. Write the chemical formula for each of the following compounds:


• water


• silica


• carbon dioxide


• methane




2. Draw a diagram to represent the molecular structure of dry water powder.
3. Draw a diagram to represent the structure of hydrated carbon dioxide.
4. Explain how water can absorb carbon dioxide.
5. Explain how silica can absorb carbon dioxide.
6. Explain why dry water is so much better at absorbing carbon dioxide than either pure water or silica.
7. Write a chemical equation to represent the production of hydrated methane.
8. Using the equation above, discuss how dry water could be used to store and release methane for use in vehicles powered by natural gas.
   

Beads of Saliva

You can stretch a glob of saliva between your thumb and forefinger. Before the strand of spittle breaks, a string of beads is formed.

Saliva, and other complex viscoelastic fluids like shaving cream and shampoo, contain long chains of molecules called polymers. In the case of saliva, the polymers are proteins known as mucopolysaccharides.

Key factors involved in the beading mechanism are :

• fluid inertia, or the tendency for a fluid to keep moving unless acted upon by an external force
• viscosity, or the time it takes a stretched polymer to 'relax' or snap back to its original shape when the stretching ceases
• capillary time, or how long it would take for the surface of the fluid strand to vibrate if plucked

In order to form beads the fluid inertia has to be large enough and the relaxation time has to be small enough. Bead formation depends on two ratios:

• the viscous force compared to the inertial force
• the relaxation time compared to the capillary time

Learning how to control bead formation could be used to improve printing because smearing 'satellite' beads form around droplets produced by an inkjet printer. Understanding bead formation could also help improve industrial processes such as electrospinning which is used to make a variety of products, and spray coating used in painting.

Reference:
Pradeep P. Bhat, Santosh Appathurai, Michael T. Harris, Matteo Pasquali, Gareth H. McKinley, Osman A. Basaran. Formation of beads-on-a-string structures during break-up of viscoelastic filaments. Nature Physics, 2010; DOI: 10.1038/nphys1682

Activities

1. Design an experiment to measure the viscosity of shampoo.
2. Suggest ways that the viscosity of shampoo could be changed.
3. Design an experiment to test one of the hypotheses above.
4. Design an experiment to measure the fluid of inertia of a range of different fluids.
   

Hydrogen: Fuel or Foe?

Hydrogen is being viewed as an eventual alternative to fossil fuels. For metals such as steel, aluminium and magnesium, commonly used in automotive and energy technology, hydrogen is less than ideal.

Hydrogen can permeate the metals when filling the tank, or during various manufacturing processes. It can infiltrate the metal lattice through corrosion, during chromium-plating of car parts, or welding, milling or pressing.

Hydrogen can make these metals brittle and their durability deteriorates leading to sudden failure of parts and components such as the fuel tank, parts of the fuel cell, and even ordinary components like ball bearings.

Scientists at the Fraunhofer Institute for Mechanics of Materials IWM in Freiburg are studying hydrogen-induced embrittlement in order to find materials and manufacturing processes that are compatible with hydrogen.

Reference:
Fraunhofer-Gesellschaft (2010, August 21). Hydrogen causes metal to break. ScienceDaily. Retrieved August 22, 2010, from http://www.sciencedaily.com­ /releases/2010/08/100816114831.htm

Study Questions

1. What is meant by the term fossil fuels?
2. Give three examples of commonly used fossil fuels.
3. Why are scientists looking at alternatives to fossil fuels?
4. Describe what is meant by a metal lattice.
5. Explain how hydrogen could infiltrate the metal lattice.
6. Explain how this infiltration of hydrogen into the metal lattice could lead to reduced ductility and brittleness.
7. List other physical properties of metals besides ductility and hardness.
8. List some chemical properties of metals.
   
9. How does steel differ from the other metals mentioned in the article above?
   

Reaction Mechanism for Ammonium Sulfates's Phase Transition

During a chemical reaction, the atoms in the reactants are rearranged to form new compounds. On a molecular level, the spatial arrangement of electrons and nuclei changes. While the structure of the reactant and product molecules can be measured the reaction mechanism, or the transient structures and molecular motions during a reaction, have remained unknown in most cases, but, this knowledge is a key element needed to understand the reaction.

Scientists at the Max-Born Institute in Berlin have now succeeded in making a "molecular movie" of the thermal phase transitions of ammonium sulfate which is a reversible reaction.

Using an advanced femtosecond laser system which generates a blue pulse of 50 femtosecond duration, they initiated the chemical reaction and then probed the structure of the excited material with high spatial resolution using a synchronised X-ray flash of 100 femtosecond duration. The X-ray pulse is diffracted off a powder made of small crystals, this is known as the Debye-Scherrer method. By simultaneously measuring the many different X-ray reflections they reconstructed the transient distances of atomic lattice planes and in turn the three dimensional distribution of electronic charge within the crystal. The "molecular movie" was created by taking X-ray snap shots at various times after triggering the reaction.

What they found is that the blue flash caused a release of both a proton from the ammonium ion and an electron from the sulfate ion. The proton and the electron then merged to form a hydrogen atom which jumped back and forth between two distant spatial positions.

Reference:
Michael Woerner, Flavio Zamponi, Zunaira Ansari, Jens Dreyer, Benjamin Freyer, Mirabelle Prémont-Schwarz, Thomas Elsaesser. Concerted electron and proton transfer in ionic crystals mapped by femtosecond x-ray powder diffraction. The Journal of Chemical Physics, 2010; 133 (6): 064509 DOI: 10.1063/1.3469779

Study Questions

1. Give the molecular formula for ammonium sulfate.
2. What is the oxidation state (oxidation number) for nitrogen in the ammonium ion?
3. What is the oxidation state (oxidation number) for sulfur in the sulfate ion?
   
4. Write a chemical equation for the overall reaction for the thermal phase transition of ammonium sulfate.
5. What is meant by the term reversible reaction? Explain your answer using the chemical equation above.
6. Draw Lewis structures (electron dot diagrams) for the ammonium ion and the sulfate ion.
7. Draw Lewis structures (electron dot diagrams) for each of the ions above immediately after the laser's blue flash initiates the reaction.
8. Using the new species above, give the oxidation state (oxidation number) for nitrogen and sulfur after the reaction is initiated. Compare these oxidation states to those in questions 2 and 3. Is this an example of a redox reaction? Explain your answer.
9. Define the terms Bronsted-Lowry acid and Bronsted-Lowry base.
10. Are any of the species described in the reaction mechanism for the thermal phase transition of ammonium sulfate acting as Bronsted-Lowry acids or Bronsted-Lowry bases. Explain your answer.
11. Define the terms Lewis acid and Lewis base.
12. Are any of the species described in the reaction mechanism for the thermal phase transition of ammonium sulfate acting as Lewis acids or Lewis bases. Explain your answer.

Hexagonal Boron Nitride

Graphene, a single-atom thick allotrope of carbon and an electrical conductor, is considered to be a possible successor to silicon in microelectronics applications.
Hexagonal boron nitride (h-BN) is an insulator. It is highly elastic and nearly as strong as graphene. Rice University scientists have found a way to implant sheets of h-BN into sheets of graphene, which controls the sheet's electronic character.
They have also found a way to deposit sheets of pure h-BN, 1 to 5 atoms thick, onto a copper substrate using a chemical vapour deposition process at about 1,000^oC. The h-BN material can then be transferred to other substrates. The size of h-BN sheets is limited only be the size of the copper foil and furnace used to grow it.
It should be possible to draw microscopic patterns of graphene and h-BN, useful in creating nanoscale field-effect transistors, quantum capacitors or biosensors.

Reference:
Li Song, Lijie Ci, Hao Lu, Pavel B. Sorokin, Chuanhong Jin, Jie Ni, Alexander G. Kvashnin, Dmitry G. Kvashnin, Jun Lou, Boris I. Yakobson and Pulickel M. Ajayan. Large Scale Growth and Characterization of Atomic Hexagonal Boron Nitride Layers. Nano Letters, 2010; 100722142755098 DOI: 10.1021/nl1022139

Study Questions

1. What is meant by the term allotrope?
2. What are the naturally occurring allotropes of carbon?
3. In what ways are these allotropes of carbon the same?
4. In what ways are these allotropes of carbon different?
5. If the formula for boron nitride is BN, what is the oxidation state (number) of boron?
6. Given the name hexagonal boron nitride, draw a possible Lewis Structure (electron dot diagram) for hexagonal boron nitride.
7. In what ways are graphite and hexagonal boron nitride the same?
8. In what ways are graphite and hexagonal boron nitride different?
9. Why is graphite a conductor while hexagonal boron nitride is an insulator?