Which suggests that we can infer water temperature in nature by observing the shape of its melting ice.
Scott Weady, Joshua Tong, Alexandra Zidovska, and Leif Ristroph (2022); Anomalous Convective Flows Carve Pinnacles and Scallops in Melting Ice. Phys. Rev. Lett 128(4)https://doi.org/10.1103/PhysRevLett.128.044502
Why are the physical properties, such boiling point and solubility, of an alkanenitrile so similar to that of a primary alkanol with the same number of carbon atoms in the hydrocarbon chain?
Why do alkanenitriles react with so many different reactants?
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Aldehydes and ketones contain the same functional group, for example, butanal and butanone both contain the same carbonyl functional group (C=O). So how would you tell if a substance was butanal or butanone?
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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 29.8oC and its boiling point is about 2204oC. This means that at temperatures between 29.8oC and 2204oC 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 30oC, 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 25oC, 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.
Use the Periodic Table to find the following for gallium:
symbol
atomic number
atomic mass
With reference to the Periodic Table explain why Mendeleev would have named the unknown element, located where gallium is now known to be, ekkaaluminium.
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
Give the most likely name for each of the following:
GaH3
Ga(NO3)3
Ga2(CO3)3
Does the video show a chemical or a physical process? Explain your answer.
Sketch a temperature vs time curve to describe the melting of gallium.
Convert the melting point and boiling point of gallium from centigrade to kelvin.
Mercury has a melting point of about 234K and a boiling point of around 630K. Convert these temperatures to oC
Explain why mercury is a liquid at room temperature and pressure.
Could you freeze mercury by walking into an air-conditioned room like you can gallium? Explain your answer.
Fog forms on a surface when water vapor in the air condenses in fine droplets. The fog that forms on glasses is not a continuous film, rather, it consists of tiny droplets of water that coalesce on the surface and reduce light transmission. A good anti-fog coating should prevent the formation of these droplets. Existing anti-fog coatings can't withstand repeated washings so must be re-applied regularly.
Researchers have used polyvinyl alcohol, a hydrophilic compound that allows water to spread uniformly, in the first reported permanent anti-fogging coating.
Four successive layers of molecules, which formed strong bonds with their adjoining layers, were applied to the surface prior to adding the anti-fog compound over this base. The result was a thin, transparent, multilayered coating that does not alter the optical properties of the surface on which it is overlaid. In addition, the chemical bonds that join the different layers ensure the hardness and durability of the entire coating.
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
Give the molecular formula for ammonium sulfate.
What is the oxidation state (oxidation number) for nitrogen in the ammonium ion?
What is the oxidation state (oxidation number) for sulfur in the sulfate ion?
Write a chemical equation for the overall reaction for the thermal phase transition of ammonium sulfate.
What is meant by the term reversible reaction? Explain your answer using the chemical equation above.
Draw Lewis structures (electron dot diagrams) for the ammonium ion and the sulfate ion.
Draw Lewis structures (electron dot diagrams) for each of the ions above immediately after the laser's blue flash initiates the reaction.
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.
Define the terms Bronsted-Lowry acid and Bronsted-Lowry base.
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.
Define the terms Lewis acid and Lewis base.
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.
The question of what happens when a material composed of more than one phase or state is heated or cooled is very important. Many metal parts, for example, are made by casting. In the casting process liquid metal is poured into a mold and solidifies into the shape of the mold. As the liquid metal solidifies it forms tree-like structures called dendrites, and, if one of the dendrites breaks off it can lead to a change in the properties of the solidified material. The airplane industry has spent a long time developing solidification methods to avoid this problem when casting jet turbine blades. Polymer solar cells use a complicated mixture of two polymers. When heated, the mixture evolves by a process that involves pinching which ultimately alters the properties of the mixture and the efficiency of the solar cell. Scientists have been observing the heating process during which a rod-like phase or state embedded in another will break up into smaller domains just like droplets at the end of a stream of water, resulting in changes to the properties of the material. They have found that the shape of the interfaces during break up becomes universal, independent of the material used. This now allows them to predict the dynamics of the break-up process in a vast array of materials such as steel and polymers.
Reference: Aagesen et al. Universality and self-similarity in pinch-off of rods by bulk diffusion. Nature Physics, 2010; DOI: 10.1038/nphys1737
Study Questions
Name the phase changes (changes of state) that can occur in each of the following situations:
heating a solid
heating a liquid
cooling a liquid
cooling a gas
Draw a sketch of the temperature-time graph expected for each of the following situations involving pure substances:
heating a solid
heating a liquid
cooling a liquid
cooling a gas
Explain why the temperature-time graph for the melting of ice differs from the temperature-time graph for freezing water.
Explain why the purity of a solid substance can be determined using its melting point.
Do you think the purity of a liquid substance could be determined using its freezing point? Explain your answer.
Explain what is meant by the term sublimation.
Give two examples of pure substances that undergo sublimation.
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