Let's Go SCUBA Diving

In 2021, Mitchell Goodwin, an experienced SCUBA diver, was diving off the coast of Mandurah in Western Australia. According to the report in the "West Australian", he descended to a depth of 42 m and stayed at this depth for 27 minutes. On his ascent, he made one decompression stop. When he got back to the boat he felt nauseous, lost his hearing, his sight, and blacked out.

What had gone wrong?

Read more in the June 2022 edition of AUS-e-NEWS.

Subscribe to AUS-e-NEWS, AUS-e-TUTE's free quarterly newsletter for chemistry students and teachers, at https://www.ausetute.com.au/ausenews.html

Nitrogen vs Air in Car Tyres

The tread on my car tyres had worn down, so I popped into my local tyre retailer to buy 4 new tyres.

"We can inflate your new tyres with air, or, for an extra $5 per tyre we can fill them with nitrogen gas", the sales person told me, " Nitrogen gas doesn't react with tyre and rim material so your tyres will last longer, it will help maintain the pressure in your tyres so you won't need to check your tyre pressure as often, and it reduces the running temperature of the tyres so your tyres are less likely to explode."

Is this just marketing hype or are there good reasons for choosing to inflate your car tyres with nitrogen instead of air?

Read the March 2020 edition of AUS-e-NEWS to find out more.

Subscribe to AUS-e-NEWS, AUS-e-TUTE's free quarterly newsletter for chemistry teachers and students, at https://www.ausetute.com.au/ausenews.html

Gutful of Gas

People can eat interesting things.
In the 1960s in Australia, Leon Samson was eating razor blades to amuse audiences, he even started to eat, slowly, in bits, a car for a bet. A little later, France produced Michel Lotito who was also eating odd things to entertain us, including an airplane between 1978 and 1980.

A razor blade is made out of steel, a particular kind of steel known as razor blade steel. A 2.61 gram razor blade contains between about 13% chromium, 0.6% carbon, and  the rest is iron. Samson would chew up a razor blade and swallow it.

After leaving the mouth, the chewed-up bits of razor blade travel to the stomach. An empty stomach has a volume of about 75 mL but when we eat the volume of the stomach can expand out to about 1 L. Protein-digesting enzymes known as proteases are released into the stomach to help begin the break up of the proteins like you find in meat, fish, eggs and cheese. The optimum pH for these proteases is at about pH 2, so hydrochloric acid is also released into the stomach.

So the small bits of razor blade now find themselves surrounded by hydrochloric acid. Hydrochloric reacts with metals, like the iron in steel, to produce hydrogen gas. Now gases have an interesting property, they expand out to fill the available space. This suggests that eating razor blades might result in a feeling of being bloated. Thankfully, it appears that it takes about 24 hours for the complete reaction between a razor blade and hydrochloric acid in the stomach, plenty of time to remove the gas build-up via burping or, um, farting.

Hydrogen gas is commonly found in our intestines, along with other gases like carbon dioxide, oxygen and nitrogen. Some of these gases get there when we swallow air along with our food and drink, but they also come from chemical reactions inside our bodies. If our bodies are healthy and working well, all the usual gases will be present in the usual concentration, but if there is something wrong, if we are sick, the nature and composition of the gases will change.

Researchers at RMIT University in Melbourne, Australia, have developed and trialed an "ingestible electronic capsule" which is capable of sensing and measuring the gases in the gut like hydrogen, carbon dioxide and oxygen. These capsules offer a new, non-invasive way to monitor the health of our gut. The capsules can be collected after they have been excreted (apparently painlessly).

Reference: 
Kourosh Kalantar-Zadeh, Kyle J. Berean, Nam Ha, Adam F. Chrimes, Kai Xu, Danilla Grando, Jian Zhen Ou, Naresh Pillai, Jos L. Campbell, Robert Brkljača, Kirstin M. Taylor, Rebecca E. Burgell, Chu K. Yao, Stephanie A. Ward, Chris S. McSweeney, Jane G. Muir, Peter R. Gibson. A human pilot trial of ingestible electronic capsules capable of sensing different gases in the gut. Nature Electronics, 2018; 1 (1): 79 DOI: 10.1038/s41928-017-0004-x

Suggested Further Reading 
Experimental Design: http://www.ausetute.com.au/experimentd.html
Name and Formula of Binary Covalent Compounds: http://www.ausetute.com.au/namcform.html
Percentage Composition:  http://www.ausetute.com.au/percentc.html
Mass-moles Calculations: http://www.ausetute.com.au/massmole.html
Molar Gas Volume Calculations: http://www.ausetute.com.au/molarvol.html
Ideal Gas Law Calculations:  http://www.ausetute.com.au/idealgas.html
Metal + Non-Oxidising Acid Reaction: http://www.ausetute.com.au/metalhcl.html
Hydrogen Ion Concentration of Strong Acids: http://www.ausetute.com.au/hstronga.html 
Reaction Calculations: Mass and Moles http://www.ausetute.com.au/molreact.html 

Suggested Study Questions

1.   Design an experiment to determine how long it would take for a razor blade to react completely with the hydrochloric acid in the stomach. Investigate ways to speed up, or, to slow down, this reaction.
2. Give the formula for each of the following:
   • hydrogen gas
   • nitrogen gas
   • oxygen gas
   • carbon dioxide gas
   • hydrochloric acid
3.   Determine the percentage composition of each of the following compounds
   • hydrogen chloride gas
   • carbon dioxide gas
4. From the information in the article, calculate the mass of each of the following elements found in a razor blade:
   • iron
   • chromium
   • carbon
5. Using the information above, calculate the moles of each of the following elements found in a razor blade:
   • iron
   • chromium
   • carbon
6. Calculate the moles of hydrogen gas that occupy the entire volume of a "full" stomach under the following conditions:
   • 0^oC and 100 kPa
   • 25^oC and 100 kPa
   • 37^oC and 100 kPa
7. Write a balanced chemical equation for the reaction between the hydrochloric acid in the stomach and the iron in a razor blade.
8. Calculate the concentration of acid released into the stomach using the information in the article. 
9. Use the balanced chemical equation to determine the volume of hydrogen gas produced when all the iron in a razor blade has reacted with hydrochloric acid.
10. Consider all the information in the article, and the calculations you have performed so far. Explain why it takes 24 hours for a razor blade to be completely digested in the stomach.

Bioethanol Fireplaces

Ethanol burners are becoming very popular in homes in Australia, often sold as "bioethanol" fireplaces. Although how "bio" your ethanol is really depends on which brand of ethanol or methylated spirits you choose to buy.
Having got some advertising mileage out of sticking the prefix "bio" onto ethanol, the glossy advertising brochure then adds some more enticing words like "eco", "friendly", "green" and/or "smart".
But the real selling point of the slick advertising is that you don't need a flue. No chimney, no pipes, just set your "bioethanol" fireplace up where ever you want it in the room.
Which is really very, very, interesting (for all you Chemists out there).

Chemistry of Combustion
Ethanol combusts (burns) by combining with oxygen gas in the atmosphere.
A balanced chemical equation for the complete combustion of ethanol is:

C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O

This tells us that for every 1 mole of ethanol (whether it has the "bio" prefix or not), 2 moles of carbon dioxide gas will be evolved (and yes, that's the same carbon dioxide gas that contributes to the greenhouse effect).

According to the brochure, 5 litres of "bioethanol" would last about 10 hours.
That is, 1 litre of bioethanol keeps your fire going for about 2 hours, just enough to watch a movie.
So how much carbon dioxide will be released into your room while you watch the movie?

First we can use the density of ethanol and the volume of ethanol burnt to calculate the mass of ethanol consumed:

• Density of ethanol is 0.79 g cm³ at 25^oC

• If we let 1cm³ = 1 mL

• then the mass of 1 mL of ethanol is 0.79 g

• so the mass of 1 L of ethanol = 1000 x 0.79 g = 790 g

Now we can calculate the moles of ethanol in the 1 L of "bioethanol" we burnt:

• moles = mass/molar mass

• molar mass = 2 x 12 + 6 x 1 + 16 = 46 g/mol

• so moles of ethanol in 1 L = 790/46 = 17.2 mol

Use the balanced chemical equation to calculate the moles of carbon dioxide produced:

• From the balanced chemical equation, 1 mole of ethanol burns to produce 2 moles of carbon dioxide gas.

• Therefore, 17.2 moles of ethanol burns to produce 2 x 17.2 moles of carbon dioxide gas.

• moles of carbon dioxide produced = 34.4 moles

We can then calculate the volume of carbon dioxide released into your room while you watch the movie:

• At 25^oC, 1 mole of gas occupies a volume of 24.79 L

• So, 34.4 moles of carbon dioxide occupies a volume of 34.3 x 24.79 = 853 L

853 L of carbon dioxide gas sounds like lot!
But is it really? What proportion of the "air" in your room will be carbon dioxide after 2 hours?

Let's calculate the volume of a room:

• A small room is about 3m x 3m x 3m

• or 300cm x 300cm x 300cm = 27,000,000 cm³ = 27,000 L

• So the volume of air in the room before you start burning your ethanol is 27,000 L(ignoring loss of volume due to you and the furniture )

And now we can see what proportion of the "air" in your room will be carbon dioxide after 2 hours:

• Assuming there is no ventilation in the room (all the doors and windows are closed), burning 1 L of ethanol adds about 853 L carbon dioxide gas to the room, so the total volume of gas is now 27,853 L.

• The percentage of that due to the carbon dioxide we have produced is 853/27853 x 100 = 3%

Now that's better, 3% sounds a whole better than 853 L doesn't it?
Or does it?

Did you know that at a concentration of about 1%, carbon dioxide will make you feel sleepy.
At a concentration of about 7%, you can suffocate.
Which makes you think you should probably be opening a window!
Except, wouldn't that defeat the purpose of lighting a fire to keep warm in the first place?

Suggested Study Questions:

1. Draw a structural formula for ethanol.
2. Explain the difference between complete and incomplete combustion of ethanol.
3. How you could you tell by observation whether the ethanol in your "bioethanol" fireplace was undergoing complete combustion or incomplete combustion?
4. The glossy brochure states that your "bioethanol" fireplace will not produce soot. What does this tell you about the type of combustion occurring in the fireplace?
5. If the ethanol in the "bioethanol" fireplace was undergoing incomplete combustion, would the amount of carbon dioxide produced be more or less than that produced during complete combustion?
6. Calculate the moles of carbon dioxide gas that would be produced if you burnt 1 L of "bioethanol" fuel in your fireplace in a room that measured 5m x 7m x 3m
7. What volume of the room in question 6?
8. At 25^oC, how many moles of gas are present in this room from question 6?
9. What percentage of gas in this room from question 6 would be carbon dioxide after you burn 1 L of "bioethanol"?
10. One of your friends suggests that you should take a "bioethanol" fireplace with you on your camping trip because it will be a perfect way to heat your tent. Do you agree with your friend or not? Explain your answer.

Hydrogen Peroxide in Space

Molecules of hydrogen peroxide, H₂O₂, have been found for the first time in interstellar space by astronomers using the European Southern Observatory-operated APEX telescope in Chile.
The hydrogen peroxide has been detected in a region of our galaxy about 400 light-years away where it is very cold (around -250^oC) and contains dense clouds of cosmic gas and dust in which new stars are being born. The clouds are mostly made of hydrogen, but contain traces of other chemicals, and are prime targets for astronomers hunting for molecules in space. The amount of hydrogen peroxide in the cloud is just one molecule for every ten billion hydrogen molecules.

Hydrogen peroxide is a key molecule for both astronomers and chemists. Its formation is closely linked to two other familiar molecules, oxygen and water, which are critical for life. Because much of the water on our planet is thought to have originally formed in space, scientists are keen to understand how it is created. Hydrogen peroxide is thought to form in space on the surfaces of cosmic dust grains, very fine particles similar to sand and soot, when hydrogen (H) is added to oxygen molecules (O₂). A further reaction of the hydrogen peroxide with more hydrogen is one way to produce water (H₂O).

Reference
P. Bergman, B. Parise, R. Liseau, B. Larsson, H. Olofsson, K. M. Menten, R. Güsten. Detection of interstellar hydrogen peroxide. Astronomy & Astrophysics, 2011; 531: L8 DOI: 10.1051/0004-6361/201117170

Further Reading
Lewis Structures (electron dot diagrams)
Intramolecular Forces
Intermolecular Forces
Temperature Conversions
Ideal Gas Calculations


Study Questions

1. Draw a Lewis Structure (electron dot diagram) for hydrogen peroxide.
2. Describe the nature of bonding that occurs within the hydrogen peroxide molecule.
3. The melting point of pure hydrogen peroxide is -0.43^oC . Explain why the melting point of pure hydrogen peroxide is slightly less than the melting point of pure water.
4. The boiling point of pure hydrogen disulfide, H₂S₂, is 70.7^oC while the boiling point of hydrogen peroxide is 150.2^oC. Explain why the boiling point of hydrogen peroxide is more than twice the boiling point of hydrogen disulfide.
5. Convert the following temperatures in ^oC to temperatures in Kelvin:
   • -250 ^oC
   • -0.43 ^oC
   • 70.1 ^oC
   • 100 ^oC
   • 150.2 ^oC
6. The amount of hydrogen peroxide in the cloud is just one molecule for every ten billion hydrogen molecules. Convert this to:
   • a concentration of hydrogen peroxide in parts per million.
   • a concentration of hydrogen peroxide in grams of hydrogen peroxide per kilogram of hydrogen
7. In outer space, 'atmospheric' pressure is about 100μPa Convert this to a pressure in:
   • kPa
   • atm
   • mmHg
   • Torr
8. Calculate the temperature of outer space if the atmospheric pressure of 100μPa is caused by the presence of 10 hydrogen molecules per cubic metre of space.
   
   
   
   

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.
    
    
    
    

Colouring Plastics

At a temperature of 30.1^oC and a pressure of about 73.8 bar, carbon dioxide goes into a super critical state that gives the gas solvent-like properties. In this state it can be introduced into polymers, acting as a "carrier" in which dyes, additives, medical compounds and other compounds can be dissolved:

• liquid carbon dioxide is pumped into a high-pressure container with the plastic components to be impregnated
• temperature and pressure are increased steadily until carbon dioxide reaches its supercritical state
• pressure increased to 170bar and the powdered pigment dissolves completely
• the dissolved pigment diffuses with the carbon dioxide gas into the plastic
• high-pressure container is opened, the carbon dioxide gas escapes but the pigment remains attached to the polymer

Tests have shown that nanoparticles of antibacterial agents can be impregnated into polycarbonate and that E-coli bacteria placed on the surface will be killed. Tests conducted with silica and with the anti-inflammatory active pharmaceutical ingredient flurbiprofen were also successful.

The process is suitable for use with amorphous or partially crystalline polymers such as nylon and polycarbonate, but cannot be applied to crystalline polymers.

Reference
Fraunhofer-Gesellschaft (2011, January 4). Impregnating plastics with carbon dioxide. ScienceDaily. Retrieved January 10, 2011, from http://www.sciencedaily.com­ /releases/2011/01/110103110206.htm

Further Reading
Temperature Conversions
Chemical and Physical Changes
Lewis Structures
Molecule Polarity
Intermolecular Forces
Ideal Gas Law

Study Questions:

1. Convert the information provided in the dot points in the article into a flow chart.
   
2. Give the molecular formula for carbon dioxide.
3. Draw a Lewis Structure (electron dot diagram) for carbon dioxide.
4. Is carbon dioxide a polar or non-polar molecule? Explain your answer
5. What type of solvents would be the best to use to dissolve carbon dioxide?
6. What type of solutes do you expect to dissolve in carbon dioxide? Explain your answer.
7. Given that 1bar is equivalent to 100kPa, convert the following pressures in bars to pressures in atmospheres:
   
   • 73.8bar
   • 170bar
8. At 25^oC and 1 atmosphere pressure, 1 mole of gas has a volume to 24.47L. Assuming ideal gas behaviour, what volume would this gas occupy at 30.1^oC and 73.8bar?
9. Calculate the volume of gas above at the same temperature but at a pressure of 170bar.
10. Calculate the volume per molecule of carbon dioxide gas in question in 9.
11. Do you think it is reasonable to assume ideal gas behaviour at this temperature and pressure? Explain your answer.
12. What do you think the term "supercritical state" as used in this article might mean?