Chlorine as a Chemical Weapon

World War I, saw the birth of the ANZAC legend*, and also the widespread use of "chemical warfare".

The first gas used by the German military as a killing agent was chlorine gas, also known as bertholite at this time.

Chlorine is a powerful irritant, which can damage the eyes, nose, throat, and lungs. Prolonged exposure to high concentrations, 1,000ppm, can cause death by asphyxiation.
Chlorine gas reacts with water in the tissues of the body to produce hydrochloric acid:

2Cl_2(g) + 2H2O_(l) → 4HCl_(aq) + O_2(g)

The chlorine gas was released from cylinders facing the enemy trenches in a favourable wind. The grey-green cloud of chlorine gas would then drift across the enemy positions.
The density of chlorine gas at 0^oC and 101.3kPa (1 atm) is 3.2g/L, while the density of air at the same temperature and pressure is 1.2754 g/L. Because chlorine gas is more dense than air, it would be more concentrated at the bottom of the trench, and less concentrated at the top. Those who suffered the worst effects were often the wounded lying on the ground or on stretchers.

Initially, German troops were issued with gauze pads filled with cotton, and bottles of bicarbonate solution. When the chlorine gas was to be released, the soldiers would dampen the gauze pad with the bicarbonate solution and breathe through it. The bicarbonate would neutralize the hydrochloric acid produced. If sodium bicarbonate solution were used, the reaction would be:

HCl_(aq) + NaHCO_3(aq) → NaCl_(aq) + CO_2(g) + H₂O_(l)

As other gases were being developed for use as chemical weapons, the need for better protection became important. One of the earliest devices was a hood with eyepieces. The hoods could be impregnated with sodium hyposulphite (sodium thiosulfate). Sodium thiosulfate reacts with dilute acids to produce sulfur, sulfur dioxide and water:

Na₂S₂O₃ + 2HCl → 2NaCl + S + SO₂ + H₂O

The gas mask was developed later. It was composed of an impervious mask and a box respirator or canistor. Air came through the canister which contained charcoal and granules of soda-lime, a mixture of sodium hydroxide and calcium hydroxide.

*ANZAC (Australian and New Zealand Army Corps) Day is commemorated each year on 25th April, marking the anniversary of the first major military action fought by Australian and New Zealand forces during the First World War. ANZAC Day ceremonies, which are held in towns and cities all over Australia and New Zealand, typically include an introduction, a hymn, a prayer, an address, the laying of wreaths, a recitation, the Last Post, a period of silence, and either the Rouse or the Reveille, and the national anthem. Anzac Day has evolved to acknowledge the sacrifice and service of subsequent wars.

Further Reading
Temperature Conversions
Density Calculations
Elements and Compounds
Writing Ionic Formula
Balancing Chemical Equations
Molecular Mass
Definitions of a Mole
Ideal Gas Law
Acid-Base Titration Calculations

Study Questions

1. Draw a table listing each element and each compound mentioned in the article above.
2. In April 1915, the German Army is said to have stockpiled 168 tons of chlorine which was contained in 5,370 cylinders. on average:
   • how many kilograms of chlorine gas was contained in each cylinder?
   • how many moles of chlorine gas was contained in each cylinder?
   • what volume would this moles of gas occupy at 25^oC and 101.3 kPa (1 atm)?
     
3. Using your calculations in part 2, calculate the density of chlorine gas at 25^oC and 101.3 kPa (1atm) in g/L.
4. Compare the density of chlorine gas calculate in part 3, to the density of chlorine gas given in the article above. Account for the difference in the two density values.
5. Convert 1,000ppm chlorine gas to a concentration in:
   • mg/L
   • g/L
   • mol/L
6. What mass of HCl could be produced from 1L of 1,000ppm chlorine gas?
7. What mass of sodium bicarbonate would be necessary to neutralize the amount of hydrochloric acid produced in question 6 above?
8. What mass of sodium thiosulfate would be necessary to neutralize the amount of hydrochloric acid produced in question 6?
9. Write a balanced chemical equations for:
   • the reaction between hydrochloric acid and calcium hydroxide
   • the reaction between hydrochloric acid and sodium hydroxide
10. Explain why a gas mask containing soda-lime might be preferable to one containing sodium thiosulfate.
    
    
    
    

Invisible Ink

The CIA has declassified a number of documents from the first World War, some detailing the nature of invisible inks used at that time. These documents are available in the Freedom of Information Act Electronic Reading Room at cia.gov

One recipe for invisible ink was as follows
"A solution of nitrate of soda and starch in water may be carried for example in handkerchiefs or starched collars, starched shorts or anything else starched. These things being laid in this solution and then ironed. The article thus treated is later on again put in water and a solution obtained which can be used for invisible writing. The best means for developing are iodate of potassium."

And the recipe for developing the ink using potassium iodate
"Iodate of potassium, 5 grams with 100 grams of water, 2 g of tartaric acid added."

The beauty of this recipe for invisible ink is that the ingredients would be quite readily available to the spy.
Nitrate of soda (sodium nitrate) could be found in lawn fertilizers.
Iodate of potassium (potassium iodate) could be found in disinfectants.

As all science students know,
starch + iodine solution → blue-black iodine-starch complexBut a person carrying around a bottle of iodine solution may have been a bit suspicious during the war.
Potassium iodate can react with tartaric acid in aqueous solution to produce potassium iodide solution. The iodide ions released can react further with the iodate ions to produce aqueous iodine solution (I_2(aq)):
5I^-_(aq) + IO₃^-_(aq) + 6H⁺_(aq) → 3I_2(aq + 3H₂O_(l)


Reference
http://www.washingtonpost.com/world/cia-recipe-for-invisible-ink-among-newly-released-wwi-era-documents/2011/04/19/AFn5Ej7D_story.html
http://foia.cia.gov/CIAsOldest/Secret-writing-document-one.pdf
http://foia.cia.gov/CIAsOldest/Secret-writing-document-two.pdf
http://foia.cia.gov/CIAsOldest/Secret-writing-document-three.pdf
http://foia.cia.gov/CIAsOldest/Secret-writing-document-four.pdf
http://foia.cia.gov/CIAsOldest/Secret-writing-document-five.pdf
http://foia.cia.gov/CIAsOldest/Secret-writing-document-six.pdf

Further Reading
Naming Ionic Compounds
Writing Ionic Formula
Molecular Mass (Formula Weight)
Percentage Composition
Oxidation and Reduction
Oxidation States (numbers)

Study Questions:

1. Write the formula for each of the following
   
   • sodium nitrate
   • potassium iodide
     
   • potassium iodate
2. Calculate the molecular mass (formula weight) for each of the following:
   
   • sodium nitrate
   • potassium iodide
     
   • potassium iodate
3. Calculate the percentage composition of each of the following:
   
   • sodium nitrate
   • potassium iodide
     
   • potassium iodate
4. What is the oxidation state (oxidation number) of iodine in each of the following:
   
   • potassium iodide
     
   • potassium iodate
   • molecular iodine
5. In the reaction between iodide ions and iodate ions, which species are being
   • oxidized
   • reduced
6. Write half-reaction equations for each of the reactions below:
   
   • iodide → iodine
   • acidified iodate → iodine

Replacing Phosphates in Detergents

From the Sydney Morning Herald (Australia) July 17, 2011, "IN THE latest round of supermarket ''me-too-ism'', Coles and Woolworths have backed a plan to rid shelves of environmentally damaging detergents.

The supermarkets have pledged to make their home brand laundry detergents phosphate-free by next year, a year ahead of a pledge this month by discount supermarket chain Aldi to ban the chemicals, which have been linked with damage to waterways and marine life."

Sodium phosphates have often been added to detergents as a builder, or water softener. Builders are chemical compounds that remove calcium ions from solution by complexation or precipitation.

The sodium phosphates that have been used as builders include orthophosphates and complex phosphates:

1. Orthophosphates which precipitate out metallic ions such as calcium:
• trisodium phosphate, Na₃PO₄
• disodium phosphate, Na₂PO₄
2. Complex phosphates which produce metallic complexes with metallic ions that do not necessarily precipitate out of solution:
   
• tetrasodium pyrophosphate Na₄P₂O₇
• sodium tripolyphosphate (STPP) Na₅P₃O₁₀
• sodium tetraphosphate Na₆P₄O₁₃
• sodium hexametaphosphate (NaPO₃)₆

Sodium tripolyphosphate (STPP), the main detergent phosphate, is something of a wonder ingredient for detergents, helping to maintain pH, remove food and grease, inhibit corrosion, and suspend insoluble dirt. For the consumer, its main visible benefit was to reduce spotting and filming by sequestering calcium and magnesium ions in the wash water.

Sodium phosphates, which can make up to 50% of the weight of a detergent, can lead to problems with eutrophication of lakes and streams, resulting in the growth of algal blooms, killing fish and plants.

On July 1, 2010, major cleaning product manufacturers finished removing phosphates from all home automatic dishwasher detergents sold in the U.S. a result of new laws in 16 states, but consumers living in areas with hard water were not happy with many of the new phosphate-free products. Phosphate alternatives such as zeolites leave residue on dishware while citrates are expensive and don’t work as well.

In order to replace the effectiveness of phosphates, a long list of additives is used which can include:

• sodium citrate which helps maintain the proper pH level of the detergent helps immobilize soils that have been removed during the wash
  
• polyacrylates which are polymers designed to bind with calcium and magnesium ions, allowing the detergent to better perform
  
• tetrasodium etidronate which is also used as a water softening agent
  
• phosphonates which are also a water softening agents, but, although they contain phosphorus, the toxicity of phosphonates to aquatic organisms is low.
  

Reference:

http://www.smh.com.au/environment/conservation/phosphates-are-all-washed-up-20110416-1dijs.html#ixzz1JkEcsejm

Further Reading

Detergents

Naming Ionic Compounds

Writing Ionic Formula

Molecular Mass Calculations

Percentage Composition

Concentration (molarity)

Concentration (ppm)

Study Questions

1. Calculate the molecular mass (formula weight) of each of the following compounds:
• trisodium phosphate, Na₃PO₄
• disodium phosphate, Na₂PO₄
• tetrasodium pyrophosphate Na₄P₂O₇
• sodium tripolyphosphate (STPP) Na₅P₃O₁₀
• sodium tetraphosphate Na₆P₄O₁₃
• sodium hexametaphosphate (NaPO₃)₆
2. Calculate the percent by mass of phosphorus present _{in each of the following compounds:}
   
• trisodium phosphate, Na₃PO₄
• disodium phosphate, Na₂PO₄
• tetrasodium pyrophosphate Na₄P₂O₇
• sodium tripolyphosphate (STPP) Na₅P₃O₁₀
• sodium tetraphosphate Na₆P₄O₁₃
• sodium hexametaphosphate (NaPO₃)₆
3. Write the formula for each of the following
   
• tripotassium phosphate
• dipotassium phosphate
• tetrapotassium pyrophosphate
• potassium tripolyphosphate
• potassium tetraphosphate
• potassium hexametaphosphate
  
4. What do each of the following prefixes mean?
   • di
   • tri
   • tetra
   • hexa
   • poly
   
   
5. Assuming a particular brand of detergent, ABC, contains 35% by mass of sodium tripolyphosphate (STPP) Na₅P₃O_{10, how much phosphorus would be present in 10 grams?}
6. _{If 10g of ABC were placed in a dishwasher which used 60L of water to wash the dishwashers, what would be the concentration of ABC detergent in mol/L?}
7. _{Using the information in question 4, calculate the concentration of phosphorus in the wash water, in parts per million.}
   

Methane Reactions

By using gold dimer cations as catalysts, Georgia Institute of Technology and the University of Ulm scientists have converted methane into ethene at room temperature, and into methanal at temperatures below 250K (-9^o F). In both the room temperature reaction-producing ethene, and the methanal generation colder reaction, the gold dimer catalyst is freed at the end of the reaction, thus enabling the catalytic cycle to repeat again and again.

The temperature-tuned catalyzed methane partial combustion process involves activating the methane carbon-to-hydrogen bond to react with molecular oxygen.
In the first step of the reaction process, methane and oxygen molecules coadsorb on the gold dimer cation at low temperature.
Subsequently, water is released and the remaining oxygen atom binds with the methane molecule to form methanal.
If done at higher temperatures, the oxygen molecule comes off the gold catalyst, and the adsorbed methane molecules combine to form ethene through the elimination of hydrogen molecules.

Reference
Sandra M. Lang, Thorsten M. Bernhardt, Robert N. Barnett, Uzi Landman. Temperature-Tunable Selective Methane Catalysis on Au2 : From Cryogenic Partial Oxidation Yielding Formaldehyde to Cold Ethylene Production. The Journal of Physical Chemistry C, 2011; 115 (14): 6788 DOI: 10.1021/jp200160r

Further Reading
Balancing Chemical Equations
Nomenclature
Combustion of Hydrocarbons
Oxidation and Reduction
Oxidation States (Numbers)

Study Questions

1. Write the molecular formula for each of the following:
   
   • methane
   • methanal
   • ethene
2. Draw the structural formula for each of the following:
   
   • methane
   • methanal
   • ethene
3. On the structural formula above, identify the functional groups present in methanal and ethene.
   
4. The following molecules are known by other names. Give atleast one other name used for each of the following:
   
   • methane
   • methanal
   • ethene
5. Write a balanced chemical equation for each of the following reactions involving the gold dimer cation catalyst:
   
   • methane and oxygen react to form methanal and water
     
   • methane and oxygen react to form ethene and water
6. Classify each reaction above as an oxidation or a reduction reaction. Justify your answer.
   
7. Write balanced chemical equations to represent the combustion of methane at high temperature, without the aid of a catalyst, under each of the following conditions:
   
   • excess oxygen
   • excess methane
8. Compare the chemical equations in question 7 to those in question 5. In what ways are the reactions similar? In what ways are the reactions different?
   

Germanium

The element germanium, symbol Ge and atomic number 32, is part of a frequently studied group of elements, Group IVa of the periodic table, which could have applications for next-generation computer architecture. It is currently used in fiber-optic systems, specialized camera and microscope lenses, circuitry, and solar cells. It is a semi-conductor so it is useful in electronics.

In 1869, Dmitri Mendeleev predicted the existence of an element in Germanium's position in his periodic table and called the element eka-silicon. Mendeleev predicted the properties of this undiscovered element based on the properties of the elements around it. In 1886 Clemens Winkler found the element in the mineral argyrodite, named it after his homeland, Germany, and reported its properties. Winkler's observed properties for germanium agreed very well with Mendeleev's predictions for ekasilicon:

Property	Ekasilicon	Germanium
atomic mass	72.64	72.59
density (g/cm3)	5.5	5.35
melting point (°C)	high	947
color	gray	gray
oxide type	dioxide	dioxide
oxide density (g/cm3)	4.7	4.7
oxide activity	weak base	weak base

Germanium can form compounds similar to those formed by carbon and silicon.
Germane, GeH₄, is a compound similar in structure to methane, CH₄.
Polygermanes with general formula Ge_nH_2n+2, where n is 1 to 5, are known.

Germanium is a semiconducting solid at room temperature and pressure. It has been predicted that, under pressure, the element should exhibit superconductivity, meaning that there is no resistance to the flow of an electric current.

Scientists at the Geophysical Laboratory at Carnegie Institution for Science have recently discovered that under pressure of 66 GPa (about 650,000 atmospheres), germanium undergoes a structural change from one type of solid material to another that is metallic, meaning it conducts electricity.

Reference
Xiao-Jia Chen, Chao Zhang, Yue Meng, Rui-Qin Zhang, Hai-Qing Lin, Viktor Struzhkin, Ho-kwang Mao. β-tin→Imma→sh Phase Transitions of Germanium. Physical Review Letters, 2011; 106 (13) DOI: 10.1103/PhysRevLett.106.135502

Further Reading
Periodic Table
History of the Periodic Table
Metals and Non-metals
Naming Carbon Compounds

Study Questions

1. Give the name and symbol for each element present in Group IVa of the Periodic Table.
   
2. Germanium is known to form germanium dioxide. Write the formula for germanium dioxide.
3. Which of the other Group IVa elements form dioxides? Give the name and formula for each of these compounds.
4. Could germanium form any other oxides? Explain your answer.
5. Draw up a table listing the electrical conductivity of each of the Group IVa elements. Explain any trend that you see.
6. Draw a structural formula for germane.
7. Explain why it would be predicted that germanium could form "polygermanes" similar to carbon's alkanes.
8. Predict the formula for the compound(s) formed between germanium and chlorine. Explain each prediction.
   

PCL : polycaprolactone

Polycaprolactone (PCL) is a biodegradable polyester used in medical devices and disposable tableware. It is produced using the caprolactone monomer and a suitable catalyst as shown below:


The catalyst used to help bring about this polymerization reaction is usually an organic tin-based catalyst such as tin (II) ethylhexanoate:
The tin (II) ethylhexanoate catalyst is highly toxic and has to be disposed of appropriately.

Biochemists found a more environmentally friendly catalyst in the form of an enzyme produced by a yeast strain known as Candida antartica. In a standard batch process, the raw materials such as caprolactone monomers and a solvent such as toluene, are dumped into a vat, along with tiny beads that carry the enzyme, and stirred. This process is too inefficient to be used commercially, and the enzyme residue is a contaminant in the final polymer product.

Researchers at the National Institute of Standards and Technology (NIST) and the Polytechnic Institute of New York University are now studying the use of a new catalyst, a small block of aluminium with a tiny groove carved into it containing the enzyme coated beads.

In this continuous flow process, the feedstock chemical flows through the narrow channel, around the enzyme-coated beads, and is polymerized out the other end. This arrangement accelerates the rate of reaction and improves the ability to recover the enzyme and reduce contamination of the product.

Reference
Santanu Kundu, Atul S. Bhangale, William E. Wallace, Kathleen M. Flynn, Charles M. Guttman, Richard A. Gross, Kathryn L. Beers. Continuous Flow Enzyme-Catalyzed Polymerization in a Microreactor. Journal of the American Chemical Society, 2011; : 110325123921095 DOI: 10.1021/ja111346c

Further Reading
Polymers and Polymerization
Enzymes
Functional Groups
Esters
Ligands and Complex Ions
Reaction Rate
Intermolecular Forces

Study Questions

1. What is the molecular formula for each of the following:
   
   • caprolactone
   • ethylhexanoate
2. When caprolactone monomers react to form polycaprolactone, the ring structure must open up. Draw a diagram of this open-ring structure.
3. On the diagram of the open-ring caprolactone structure, identify and name the functional groups present.
4. Draw a diagram of showing how 3 caprolactone monomers join together to form part of the polycaprolactone polymer.
5. On the diagram of the polycaprolactone polymer you have drawn, identify and name the functional groups present.
6. Why do you think it is common for industrial chemists to look to naturally occurring enzymes to replace more environmentally hazardous metal-based catalysts?
   
7. Why do you think the caprolactone polymerization reaction is carried out in an organic solvent like toluene rather than in water?