Martian Elements

NASA's Mars Science Laboratory rover, Curiosity, is due to be launched between November 25^th and December 18^th 2011 and should land on Mars in August 2012. Curiosity will carry a next generation, onboard "chemical element reader" to measure the chemical ingredients in Martian rocks and soil.

The Alpha Particle X-Ray Spectrometer (APXS) instrument uses alpha particles and X-rays to bombard a target, causing the target to give off its own characteristic alpha particles and X-ray radiation. This radiation is than read by an X-ray detector which reveals which elements are present in the sample, and how much of the element is present.
Scientists will use information from APXS to figure out the present and past environmental conditions that are preserved in the rocks and soils.

Currently, scientists believe that the most abundant elements on Mars are silicon and oxygen, then iron, magnesium, aluminium, calcium, and potassium, which are the elements that make up igneous rocks, the minerals that crystallize from magma. The characteristic red colour of Mars is due to the presence of iron oxides. Titanium, chromium, manganese, sulfur, phosphorus, sodium and chlorine are also present in much smaller amounts.
Hydrogen is present in water. In 2008, NASA announced that the Phoenix lander had confirmed the presence of water in the form of ice on the Martian polar ice caps.
Carbon occurs as carbon dioxide in the atmosphere, and as dry ice at the Martian poles, while some carbon is stored as carbonates. Phoenix Mars lander in 2007 found alkaline soil containing calcium carbonate, and in 2010, Mars Exploration Rover Spirit identified deposits of magnesium-iron carbonate.
About 95% of the Martian atmosphere is carbon dioxide. Nitrogen gas makes up 2.7% of the Martian atmosphere, then smaller amounts of argon, oxygen, carbon monoxide, water vapor, and nitric oxide. Tracer amounts of neon, krypton, formaldehyde, xenon, ozone and methane have also been detected.

Reference
NASA/Jet Propulsion Laboratory (2011, February 20). Advanced NASA instrument gets close-up on Mars rocks. ScienceDaily. Retrieved February 22, 2011, from http://www.sciencedaily.com­ /releases/2011/02/110220204711.htm

Further Reading
Elements and Compounds
Metals and Non-metals
Periodic Table
Radioactivity

Study Questions:

1. Draw up a table with two headings; element name and chemical symbol. Enter the name and symbol of each element named in the article above into the table.
   
2. Draw up a table with two headings, elements in Martian rocks, and, elements in Martian atmosphere. Enter each element mentioned in the article above into the table in the appropriate column.
3. Draw up a table with three headings, metals, non-metals and semi-metals (metalloids). Enter each of the elements named in the article above into the table in the correct column.
4. Use a Periodic Table to find the atomic number of each element named in the article above.
5. Name three compounds mentioned in the article above and write the chemical formula for each one.
6. Name each of the Group VIII (Noble Gases) mentioned in the article and give the chemical symbol for each one.
7. Name the organic (carbon) compounds mentioned in the article and give the molecular formula for each one.
8. What is an alpha particle?
   

Lithium for a Longer Life

Lithium is the 25^th most abundant element in the Earth's crust, with approximately 20mg of lithium present in every kilogram of crustal material. It is a soft, silvery-white metal that belongs to Group I (alkali metals). It is so highly reactive that when it is cut in air it will quickly corrode before your eyes. In the presence of water, lithium reacts to form hydrogen gas and lithium hydroxide in aqueous solution. Because it is so reactive, lithium does not occur free in nature, it only appears naturally in compounds.

Lithium-6 and lithium-7 were among the three elements synthesized in the Big Bang according to cosmological theory, the other two elements being hydrogen and helium. Lithium is present in cooler, less massive brown dwarf stars but is destroyed in hotter red dwarf stars, so its presence in the stars' line emission (atomic) spectra can be used to differentiate between these two kinds of stars in the so-called 'lithium test'.

Trace amounts of lithium ions are present in the oceans. The total lithium content of seawater is estimated to be 230 billion tonnes, and is present in concentrations of about 0.2 parts per million.
Lithium is also present in trace amounts in plants and animals. Vertebrates contain lithium in concentrations between 21 and 763 parts per billion.

Lithium salts, such as lithium carbonate, have been to shown to be useful as mood-stabilizing drugs. Therapeutically useful amounts of lithium are between 1.0 and 1.2 millimolar, which is only slightly lower than the toxic amount of 1.5 millimolar.

Scientists at the Friedrich Schiller University Jena have just demonstrated that a regular uptake of lithium could lead to a longer life. The scientists studied the impact of lithium in a concentration that is regularly found in ordinary tap water by analyzing the mortality rate in 18 adjacent Japanese municipalities in relation to the amount of lithium contained in tap water from the respective regions. They found that the mortality rate was considerably lower in those municipalities with more lithium in the drinking water.

Reference
Kim Zarse, Takeshi Terao, Jing Tian, Noboru Iwata, Nobuyoshi Ishii, Michael Ristow. Low-dose lithium uptake promotes longevity in humans and metazoans. European Journal of Nutrition, 2011; DOI: 10.1007/s00394-011-0171-x

Further Reading
Elements and Compounds
Metals and Non-metals
Trends in Group I
Electron Configuration
Naming Ionic Compounds
Writing Ionic Formulae
Parts per Million Concentration
Molarity Concentration
Emission (Atomic) Spectra
Isotopes
Relative Atomic Mass

Study Questions

1. What is the atomic number of lithium?
2. What is the simple electron configuration for an atom of lithium?
3. What is the expected charge on a lithium ion? Explain your answer.
4. Write the formula for each of these compounds:
   
   • lithium hydroxide
   • lithium carbonate
5. Write a balanced chemical equation to represent the reaction between lithium metal and water.
6. For each of the following isotopes of lithium, give the number of protons and the number of neutrons present:
   
   • lithium-6
   • lithium-7
7. Given that the relative atomic mass of lithium is 6.941, and assuming lithium-6 and lithium-7 are the only isotopes of lithium present, calculate the abundance of each isotope.
8. Convert the following to concentrations in molL^-1 (M):
   
   • 0.2ppm
   • 1.2millimolar
   • 1.5millimolar
     
   • 21ppb
   • 763ppb
9. If the total lithium content of seawater is estimated to be 230 billion tonnes, and is present in concentrations of about 0.2 parts per million, what is the mass of seawater present on Earth?
10. In the 'lithium test' for stars, what spectral lines do you expect to see in brown dwarf stars that will not be present in red dwarf stars?
    

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?
   
   

Light Bulb Elements

The traditional incandescent light bulb, currently being phased out in many countries because it is considered to be energy inefficient, is really nothing but a glass ball containing a thin filament of tungsten, a metal with a high melting point, in an inert gas such as argon. As electricity passes through the tungsten, the metal heats up and glows bright white. The argon gas prevents the tungsten coming into contact with oxygen and burning.

The compact fluorescent lamp, also known as CFL's or energy saving lights, are commonly being used to replace incandescent light bulbs because they are more energy efficient. Any fluorescent lamp is just a gas discharge tube that uses electricity to excite mercury vapour. CFL's contain between 1mg and 5mg mercury per bulb. Now, while this may not sound like much, it has been estimated that if all of the 270 million CFLs sold in the USA on 2007 were sent to landfills, this would represent about 0.13tonnes, or 0.1%, of all US mercury emissions. Mercury is a toxic metal, and, when disposed of in landfills and waste incinerators, can contribute to air and water pollution.

Light-Emitting Diodes (LEDs) are also considered strong candidates to replace energy inefficient incandescent light bulbs. LEDs consist of a semiconductor chip doped with impurities so that current flows easily in one direction but not in the reverse direction. Light is emitted when an electron falls to a lower energy level while traveling along the semiconductor. The colour of light emitted by an LED is determined by the compound the semiconductor is made of, eg, red though to yellow light is achieved using gallium arsenide phosphide, aluminium gallium indium phosphide, or, gallium (III) phosphide. However, LEDs also contain potentially hazardous substances such as lead and arsenic which are linked to several diseases such as cancers, kidney disease, skin rashes and hypertension.
University of California Irvine's Department of Population Health & Disease Prevention scientists have discovered that low-intensity red LEDs contain up to 8 times the legal amount of lead allowed in California as well as significant levels of arsenic, and that white LEDs, while containing the least amount of lead, contain high levels of nickel.

Reference
Seong-Rin Lim, Daniel Kang, Oladele A. Ogunseitan, Julie M. Schoenung. Potential Environmental Impacts of Light-Emitting Diodes (LEDs): Metallic Resources, Toxicity, and Hazardous Waste Classification. Environmental Science & Technology, 2011; 45 (1): 320 DOI: 10.1021/es101052q

Further Reading
Elements and Compounds
Metals and Non-metals
Definitions of a Mole
Ideal Gas Law
Parts per Million Concentration
Greenhouse Effect

Study Questions

1. Locate each of the elements listed below in the Periodic Table. Provide the symbol for each element.
• tungsten
• argon
• oxygen
• mercury
• lead
• arsenic
• nickel
• gallium
• phosphorus
• aluminium
• indium


2. Draw up a table using the headings metal, non-metal, and semi-metal, and place each of the elements above in the relevant column.
3. What does a Chemist mean when they refer to an inert gas?
4. Estimate the volume of an incandescent light bulb.
   • If the light bulb contains argon gas at 0.1kPa pressure, how many moles of argon are present?
   • Convert the moles of argon gas to a mass of argon gas.
5. Assume a compact fluorescent lamp contains 5mg mercury vapour at 0.3% atmospheric pressure and 25^oC.
   • How many moles of mercury does the compact fluorescent lamp contain?
   • Calculate the volume of the compact fluorescent lamp.
   • What is the concentration of mercury vapour in the CFL in parts per million?
6. There are many different ways to produce electricity; coal-fired power stations, power from uranium fission or from hydroelectricity schemes. For each of these types, discuss the impact on greenhouse gas emissions of replacing incandescent light bulbs with CFLs or LEDs.
7. If a person were to drop and break a compact fluorescent lamp at home, describe the steps that should be taken to safely clean up, and dispose of, the mess.
   
   
   

Spinach Protein Could Help Make Biofuel

Plants use photosynthesis to convert the energy of sunlight into chemical energy. Scientists would love to be able to mimic this process in order to harness the sun's energy for the production of electricity and fuel.

Scientists at the Oak Ridge National Laboratory have been studying the LHC-II protein extracted from spinach. The primary role of the LHC-II protein is as a solar collector, absorbing sunlight and transferring it to the photosynthetic reaction centres, but it can also carry out electron transfer reactions.

When LHC-II is introduced into a liquid environment containing polymers, it interacts with the polymers to form sheets similar to those found in natural photosynthetic membranes. The ability of LHC-II to force the assembly of structural polymers into an ordered, layered state, could make the development of biohybrid photoconversion systems possible. These systems would consist of high surface area, light-collecting panes that use the proteins combined with a catalyst such as platinum to convert the sunlight into hydrogen, which could be used for fuel.

Reference
Mateus B. Cardoso, Dmitriy Smolensky, William T. Heller, Kunlun Hong, Hugh O'Neill. Supramolecular assembly of biohybrid photoconversion systems. Energy & Environmental Science, 2011; 4 (1): 181 DOI: 10.1039/C0EE00369G

Further Reading
Carbon Cycle
Proteins
Oxidation and Reduction
Polymers
Fuel

Study Questions:

1. Describe the process of photosynthesis.
2. Write a chemical equation to demonstrate this process of photosynthesis.
3. What is meant by the term 'electron transfer reaction' used in the article above?
4. Is photosynthesis an example of an electron transfer reaction?
5. Many electron transfer reactions in nature. Describe one example.
6. Describe what Chemists mean when they call something a protein.
7. Explain what is meant by the term 'polymer' as used by Chemists.
8. When Chemists refer to a protein forming sheets, what type of protein structure are they referring to? Explain how this type of structure can form.
9. What is meant by the term 'catalyst'?
10. Why is a catalyst necessary for man-made systems designed to convert sunlight into hydrogen to be used as a fuel?