Click to download REDOX RULES posters for VCE Chemistry
What’s redox? We never learned that!
Yes, you did. I use the term “redox” to refer to all of the following chapters in Heinemann Chemistry 2, which you will have learned at the end of Term 3 (September).
Chapter 26: Redox (revision of Year 11)
Chapter 27: Galvanic Cells
Chapter 28: Electrolytic Cells
Don’t underestimate redox
The VCAA has consistently used redox to discriminate which schools and students have the self-discipline required to keep studying at the end of the year. Studies show that redox is taught at a time when student motivation is at its minimum: energy levels are low, emotions are high, and graduation is just over the horizon. Many schools and students gloss over these topics because they’re running out of time, any many students think they’ve grasped the topic – when they’ve actually grasped misconceptions instead.
Here are some popular redox lies (misconceptions)
LIE #1: The polarities switch during recharge Nope. The polarities never switch. It’s the labels of ‘anode’ and ‘cathode’ that switch because the electrons are flowing the other way through the external circuit. Polarity is permanent.
LIE #2: Hydrogen fuel cells don’t emit any greenhouse gases Wrong. They emit H2O, which is a powerful greenhouse gas. If you don’t believe that the VCAA can be this pedantic, think again. Read their 2015 Examiners Report here.
LIE #3: Each mole of electrons forms 1 mol Ag, 2 mol Cu or 3 mol Al in a cell Wrong again. If you look at the half-equations, you’ll see that each mole of electrons actually forms 1 mol Ag, 1⁄2 mol Cu or 1⁄3 mol Al. That’s why I teach “1, 1⁄2 and 1⁄3 moles” instead of the typical “1, 2, 3 moles” rule.
LIE #4: Temperature increases the rate of reaction in electroplating
Wrong! Remember that Faraday’s first law states that m ∝ Q. Because Q = I×t, only those two things – current and time – can affect the mass deposited at the cathode.
LIE #5: Electrons always leave the anode and go towards the cathode Wrong again. Electrons go RACO: to see what that means, download the posters above. This question appears in recent versions of Chemistry Checkpoints. Give it a try.
LIE #6: The cathode is always positive Ask your teacher.
LIE #7: Ions flow one way in the salt bridge
Nope. Anions always migrate to the anode; and cations always migrate to the cathode.
LIE #8: KOHES always works for balancing half-equations
KOHES only works for cells with acidic electrolytes. For cells with alkaline electrolytes, which sometimes appear in VCAA papers despite not being in the study design (see page 46 here), you’ll need to use KOHES(OH). Here’s KOHES(OH) explained:
Do KOHES as normal
Add the same number of OH–(aq) ions to each side of the half-equation to balance out the H+(aq)
Cancel and simplify. Remember that H+(aq) + OH–(aq) makes H2O(l). Remember also to cancel out any remaining H2O(l).
LIE #9: I can balance an unbalanced redox equation by putting numbers in the equation Don’t be fooled by this one! The ONLY way to balance an unbalanced redox equation successfully is to do the following:
Separate it into two half equations
Balance them using KOHES or KOHES(OH) as appropriate
Multiply them and recombine
Cancel and simplify
That’s a lot of work but it’s the only way to do it successfully. If you try to ‘cheat’ by just writing numbers (molar coefficients) in front of the reactants and products, you’ll find that the charges don’t add up, and you’ll get zero marks for the question.
LIE #10: I can break up polyatomic ions to make balancing half-equations easier
Nope! You’re only allowed to separate aqueous species in a half equation or an ionic equation. Because the Mn and O are actually bonded together in a polyatomic ion, you’ll need to write this:
If in doubt, keep it intact and it’ll cancel out by the end if it’s a spectator ion.
LIE #11: The two reactants that are closest together on the electrochemical series react Not always true. Use SOC SRA instead, which is explained in the posters above. Still struggling? Ask your teacher or tutor for help.
LIE #12: Oxidants are all on the top of the electrochemical series They’re actually on the left, and all the reductants can be found on the right side of each half equation in the electrochemical series. There is no top/bottom divide on the electrochemical series: only a left/right divide of oxidants/reductants.
Decorate your school/bedroom/hallway
Surround yourselves with truthful redox revision using these 17 free Redox posters. I’ve had these up around the whiteboard for a few weeks now – they’re a constant reminder to students that redox has many ideas that are always true.
One more tip: print and laminate an electrochemical series (available here) so you can annotate it during dozens of practice dozens without wasting paper. Good luck!
In 1808, a massive volcano erupted somewhere on Earth. So large was the eruption that it bellowed sulfate particles into the atmosphere that caused significant global cooling in the years that followed (Guevara-Murua 2014). Despite its gargantuan size, nobody to this day has been able to locate the volcano or find any direct eyewitness accounts of its eruption. The volcanic eruption of 1808 remains an unresolved scientific mystery to this day.
How do we know this mystery volcano ever erupted at all? The first piece of evidence is an increase in sulfuric acid concentration found in Greenland ice cores, which are a characteristic ‘chemical signature’ of sulfur-rich volcanic eruptions (Dai 1991). The only major spike in sulfuric acid concentration in Greenland ice that doesn’t align with a real volcanic eruption observed somewhere on Earth is the spike found around 1808, suggesting the existence of this mysterious volcano.
The second piece of evidence is called the ‘sulfur isotope anomaly’. Deposits of sulfur buried deep underground have a different isotopic composition compared with sulfur sources on the planet’s surface. In the same way that we can monitor the effects of fossil fuel combustion on atmospheric concentrations of carbon dioxide, we can quantify the amount of sulfur emitted from volcanoes by measuring changes in the relative quantity of sulfur-33. A huge spike in Δ33S suggests an enormous volcanic eruption occurred – and that’s exactly what we see when we study samples from the year 1808.
The third piece of evidence comes from trees. Trees grow at different rates depending on the climate. In particular, trees grow faster when it’s warmer (but not too hot, of course, which inhibits their growth somewhat), and they grow more slowly when it’s cold. Counting tree rings can reveal not only the age of the tree, but measuring the thickness of each tree ring allows researchers to estimate the amount of growth the tree accomplished in a given year. By measuring different trees in the same region, researchers can gain insight into the past climate of that particular region. Analysis of tree rings has shown that bristlecone pine trees had drastically decreased growth rates in the summer of 1809, suggesting the climate cooled significantly around that time (Salzer 2007). Cooling might have been caused by a giant volcano.
While none of this evidence amounts to a direct observation that the mystery supervolcano ever erupted, we do have eyewitness accounts of volcanic ejecta from exactly the same time. All the evidence, taken together, definitely points to the fact that the supervolcano did in fact exist. Scientists, in fact, are certain.
The first eyewitness account was written a highly respected Colombian scientist called Francisco José de Caldas, who described “a transparent cloud that obstructs the sun’s brilliance” over Colombia for several months from December 1808 to February 1809. The second eyewitness was a physician named José Hipólito Unanue who wrote about seeing “sunset afterglows” over Peru in the same time period. Both these observations are characteristic of large volcanic eruptions.
The fact that atmospheric haze was observed in both Colombia and Peru, which are in the southern and northern hemispheres respectively, suggest that this volcano was located somewhere in the tropics. These observations imply that ash was cast 2,600 km in all directions but the effect on the climate was global. One researcher is quoted as saying the mystery volcano “blanketed the planet in ash”. (Cole-Dai n.d.)
Vulcanologists rate volcanic eruptions on a scale called VEI (volcanic explosivity index), which is similar to the Richter scale for earthquakes. It’s a logarithmic scale that approximates the volume of ash that’s ejected by a particular eruption. The logarithmic nature of the scale means that while a VEI-3 eruption is called “severe”, a VEI-4 event is called “cataclysmic”. In 2010, Eyjafjallajökull erupted in Iceland, resulting in ash cloud so large that it caused severe delays to air traffic across Europe, Greenland, Russia and eastern Canada. The Eyjafjallajökull eruption was a VEI-4 (“cataclysmic”) event.
When Mount Saint Helens erupted in 1908, killing 57 people and causing $1.1 billion of damage across Canada and the US, it was classified by vulcanologists as a VEI-5 (“paroxysmic”) event. Alarmingly, the mystery volcano in 1808 was at least 10 times more devastating than Mount Saint Helens in terms of the volume of ash ejected. The mystery volcano was a VEI-6 event, and it’s described by vulcanologists as “colossal”.
Volcanic ash acts “like a giant window shade, reflecting sunlight and lowering temperatures on the ground for years afterward” (Cole-Dai n.d.). Temperatures across Europe were measurably lower in the years that followed as the ash cloud obscured incoming rays from the sun. Trees grew more slowly (as evidenced by tree ring data), harvests were diminished and the climate cooled for several years afterwards.
This cooling came at a very inconvenient time. Temperatures were already lower than usual in the northern hemisphere due to the Little Ice Age. In a further devastating blow, a second, much larger volcano erupted on April 10, 1815. It was located on Mount Tambora in Indonesia and had an intensity of VEI-7 or “super-colossal” (this is just one level away from VEI-8, which is named rather horrifyingly, “apocalyptic”). Mount Tambora’s eruption was so ‘super-colossal’ that 90% of the islanders on Tambora were killed by lava flowing down from the sky. Downpours of hot ash killed trees and fish for miles around, covering them with inches of grey dust. Hot ejecta was propelled eighteen miles into the air above the volcano producing a ‘boom’ that could be heard a thousand miles away. People across Indonesia mistook the volcanic ‘boom’ for a ship’s rescue signal or a bomb detonation. Some army officials across Indonesia’s vast archipelago even dispatched troops to defend their islands after mistaking the ongoing volcanic roar for the sound of an invading army.
The sulfur dioxide released from the super-colossal Mount Tambora explosion reacted with gases in the stratosphere to produce 100 million tons of sulfuric acid, H2SO4. The sulfuric acid condensed and remained suspended in an ‘aerosol cloud’ (basically a cloud) that was accelerated by stratospheric jet streams (basically very strong winds) until the entire globe was smeared with a thin layer of H2SO4. This is a rare event, and only happens following truly colossal volcanic eruptions. Interestingly, H2SO4 reflects incoming rays from the sun, and temperatures, which were already low as a result of the mystery supervolcano in 1808, were lowered yet again. The year 1815 was, as some writers put it, “the year without a summer”. Temperatures that year were about three degrees lower than usual across Europe, which is incredible considering that both volcanoes erupted near the equator.
If the Mount Tambora volcano was a little smaller, the sulfuric acid would have formed in the atmosphere instead, and would have rained back down to the surface as acid rain. But at stratospheric altitudes, far above the clouds, the sulfuric acid haze stayed there for years acting as a kind of sunscreen for our planet.
How does this relate to chemophobia? The combination of the Little Ice Age, the 1808 mystery eruption and the super-colossal eruption of 1815 had cooled the climate to such an extent that the weather in Lake Geneva was terrible in the summer of 1815. Who was there at the time? Mary Shelley, of course, who was staying indoors drinking because the weather was too bad to go boating. Cold, bored and disappointed at the lack of a ‘summer’ holiday, Shelley and her companions set about writing ghost stories instead. Among them was Frankenstein, which featured the original, quintessential stereotype of a mad scientist. The cliché lives on to this day.
Since 1996, there has existed a niche group of conspiracy theorists in western countries that believes that the government (or some other authority) is spraying compounds out the back of commercial/military aircraft for a plethora of reasons. Seventeen percent of Americans believe a hilariously-named “SLAP” project (secret large-scale atmospheric program) exists in the United States, and 2% are ‘certain’ of its existence. Conspiracy theorists photograph normal aeroplane contrails and upload them to the internet, calling them ‘chemtrails’, and using them as evidence of SLAP.
The conspiracy theorists cite “mind control”, “radar mapping”, and “chemical weapons testing” among suspected motives, and they even have detected elevated concentrations of barium and aluminium in soil and atmosphere at certain locations. Conspiracy theorists use these chemical data to support their belief in the SLAP idea.
Just this month, the results of a comprehensive review of all the so-called evidence for contrails was conducted – by an impressive 77 experts in atmospheric chemistry – and they’ve concluded that the conspiracy theory seems highly unlikely to be true.
First, what are contrails?
Contrails are ice-clouds that emerge from the backs of jet engines on aeroplanes. They vary in width, colour and persistence depending on the temperature, air pressure and humidity.
Combustion in jet engines produces two products: water vapour, H2O(g), and carbon dioxide, CO2(g). These gases exit the jet engine and quickly lose momentum, eventually forming a trail in the air behind the aeroplane. The freezing cold temperatures at aeroplane altitudes freezes the water vapour in its tracks (but not the carbon dioxide – it’s not that cold!). A contrail is essentially a trail of snowflakes!
What did the scientists find?
Seventy-seven experts found 100% agreement that SLAP was not the simplest/most likely explanation for the following phenomena:
Why am I mentioning this?
The ‘chemtrails’ conspiracy emerged as one of the most recent forms of chemophobia. It originated in 1996 when a paper was published by the United States Air Force called Weather as a Force Multiplier: Owning the Weather in 2025 suggested spraying compounds from aeroplanes to help engineer the climate. This seeded the conspiracy, and ebbing public trust of experts/scientists helped it to balloon out of proportion from there.
Until this study was conducted, the scientific community had no credible evidence to the contrary: we had no rebuttal to offer the ‘chemtrails’ crowd. This study finally puts the overwhelming majority of evidence (and 76 of the 77 experts involved) in favour of there being no such SLAP project – and no ‘chemtrails’ to speak of.
“The goal, the researchers say, is not so much to change the minds of hard-core believers, but to provide a rebuttal — the kind that would show up in a Google search — to persuade other people to steer clear of this idea.”
This study, it seems, is aimed at the neutral 60%. This is exactly how we need to be fighting chemophobia.
Question: Have similar studies been conducted for the other forms of chemophobia that exist?
The public uses the word ‘chemical’ to mean ‘synthetic substance’. Chemists have traditionally opposed this definition and stuck with ‘substance’ instead, responding with “everything is a chemical” in defence.
Arguing over definitions is futile and avoids the elephant in the room – that there’s been almost no public outreach to support the field of chemistry in the last few decades to counteract growing public skepticism of science (and of chemistry in particular).
Furthermore, it’s even more futile arguing over definitions when the Oxford English Dictionary provides a clear answer to this debate:
chemical (noun) – a distinct compound or substance, especially one which has been artificially prepared or purified
I ask all chemists to embrace the dictionary definition of ‘chemical’ and stop bickering with the public over definitions.
My main concern here is that if “everything is a chemical”, then it therefore follows that ‘chemophobia’ is the fear of everything, which is nonsensical. If we’re going to talk about chemophobia, we’re also going to have to accept the definition of chemical that the OED and the public have been using for a long time: that “chemical” = “artificially prepared substance”.
So what do we call non-synthetic chemicals? Try using a word with less baggage such as “molecule”, “compound”, “substance” or “element” where it’s relevant. By using these words, we avoid the natural=good/artificial=bad divide, which is the central assumption of chemophobia.
‘Chemophobia’ is an irrational aversion to chemicals perceived as synthetic.
The word ‘chemophobia’ refers to a small subset of people who are not only disenfranchised by science, but who have subscribed to alternative sources of knowledge (either ancient wisdom or – sadly – Google). Many people with chemophobia are protesting against the establishment, and this is particularly evident in the anti-GMO movement. At the core of most people who oppose GMOs is a moral/political opposition to having their food supply controlled by giant corporations. No number of scientific studies concluding the safety and reliability of GMO crops will succeed in persuading them otherwise because the anti-GMO movement is founded on moral/political beliefs, not on science. By throwing science at them, we’re wasting our time.
More important than chemophobia
The Royal Society of Chemistry’s recent report on Public Perceptions of Science showed roughly a 20-60-20 range of attitudes towards chemistry.
No matter how the RSC phrased the question, roughly 20% of the UK public who were surveyed indicated a negative attitude towards chemistry, and another 20% showed a positive attitude. The 60% in the middle felt disconnected from the subject – maybe disliked it in school – but felt neutral towards it when asked.
Chemophobia afflicts some people in the bottom 20%. They gave negative word-associations with ‘chemistry’ (e.g. ‘accidents’, ‘dangerous’ and ‘inaccessible’).That bottom 20% group is so vocal (e.g. Food Babe) that they distract chemists from the 60% in who are neutral. The ‘neutral’ crowd is a much larger audience that’s much easier to engage/persuade through outreach efforts. We should focus on talking to them.
Neil deGrasse Tyson has said in interviews that his huge TV hit show COSMOS was aimed at “people who didn’t even know they might like science”. That’s the middle 60%. Brian Cox’s amazing Wonders of the Universe was aimed at a similar audience – but chemistry has nothing similar to offer. We’re engaging those who are already interested (with academic talks and specialist journals) and we’re engaging with the bottom 20% via social media and comments on foodbabe.com… but why haven’t we started engaging the middle 60%, who gets most of their science information from TV? How many chemistry TV icons can you name? Where are the multi-channel launches of big-budget chemistry documentaries*? Chemistry is lagging far behind biology and physics in that regard.
*BBC Four’s Chemistry: A Volatile History (2010) doesn’t count – it was only three episodes long, got no further than ‘the elements’ and was presented by a PHYSICIST!
Focus on the 60% who are ‘neutral’
I ask chemists to focus on addressing the disinterested 60%. From an outreach perspective, this is much more fun and is positive rather than reactionary. By engaging those who feel neutral about chemistry, we might even empower enough of the public to fight chemophobia (online, at least) by themselves – without our direct intervention.
I urge chemists to tell the public what you do in simple terms. Describe your work to the public. Tweet about it. Participate in your university/faculty’s YouTube videos by explaining your work and its relevance. Offer advice as a science correspondent for local media outlets (many universities have ‘expert lines’ – get involved). Give your ‘talk’ at local schools – it make a HUGE difference to students’ perceptions of science. Devote 5% of your working time to doing outreach. As a teacher, I’m practically doing it full-time.
Plus, we urgently need a chemistry TV hero. Could someone do that, too, please?
James Kennedy will explore the rise of chemophobia, an irrational fear of compounds perceived as ‘synthetic’, and the damage it can cause in this interactive webinar. We’ll examine its evolutionary roots, the factors keeping it alive today and how to fight chemophobia successfully.
What You Will Learn
Origins of chemophobia as an irrational psychological quirk
Chemistry teachers, Walter White, materialism and advertisements are all fuelling chemophobia today
Fighting chemophobia needs to be positive, respectful, multifaceted, and good for consumers
AsapSCIENCE has made an awesome video called This is NOT NATURAL based on the work I’ve been doing on this site. Watch the video and read the comments thread for some insight into the discussion (and misinformation) that spreads online regarding ‘natural’ and ‘healthy’ products.
One of the most upvoted comments is actually a thinly-veiled advertisement for a book called “The Coconut Oil Secret: Why this tropical treasure is nature’s #1 healing superfood”. Click through to their product page and you’ll see why the natural/organic sector needs more regulation, and why consumers need to be better-informed.
Check out the video below, or click here to visit the comments thread on YouTube.
Shaun Holt and I recently co-wrote a paper for Research Review on the ingredients found in personal care products (e.g. shampoos, lotions and cosmetics). We analyse the recent surge in demand for ‘natural’ products and the beliefs that have been driving it.
We’re not saying that natural products don’t work – in fact, quite the opposite. We’re saying that natural products, just like synthetic ones, can be harmful, beneficial or neutral depending on the dose and upon how they’re used.
The terms “natural”, “chemical free” and “organic” are used frequently to market personal care products. However, the exact meaning of these terms is still unclear for consumers, and the use of these terms on labels is still unregulated in some markets. The purpose of this review is to provide clarity on the meanings of these terms and the implications of their application in the marketing of personal care products. The importance of applying a science-based approach to the assessment and recommendation of personal care products is also emphasised. This review is intended as an educational resource for healthcare professionals (HCPs), including nurses, midwives, pharmacists, and pharmacy assistants.
In a debut podcast, Sam Howarth discusses with chemophobia research-enthusiast and chemistry teacher, James Kennedy, the evolution of fearing chemicals and the people who are driving it behind the scenes.
Sam Howarth is a self-taught nutrition and fitness enthusiast – a fanatic learned through trial and error over 3 years of research and over 10 years of personal struggles with food and body image.
In the podcast, we talk about chemophobia, its origins and the money that keeps it alive.
We all feel a profound connection with the natural world. E O Wilson called this sensation biophilia: ‘the urge to affiliate with other forms of life’. That sense of connection brings great emotional satisfaction. It can decrease levels of anger, anxiety and pain. It has undoubtedly helped our species to survive, since we are fundamentally dependent on our surrounding environment and ecosystem. But lately, biophilia has spawned an extreme variant: chemophobia, a reflexive rejection of modern synthetic chemicals.
Recall from last week that our Periodic Table Smoothie contains the following species:
Amount present (moles)
Pressure: 718 kPa Temperature: 350 °C
Reactions of nitrogen in our 10-litre vessel
Our freshly-added 1.00 mol of nitrogen gas, N2(g), reacts with hydrogen gas to make ammonia in the following reversible (equilibrium) reaction. We will assume that the interior metal surface of the vessel is a suitable catalyst for this reaction (e.g. iron).
There are three other reactions below that might have occurred at higher temperature, but I’ve chosen not to raise the temperature of the vessel at this point. Rather, we’ll keep it at 350 °C to keep things manageable.*
*I was tempted at this point to elevate the temperature of our vessel to 500 °C so that the second reaction could take place as well. This would produce copious amounts of smelly ammonia gas, which would allow for larger quantities of interesting organic compounds to be produced later on. To keep our simulation safe and (relatively) simple, I’ve decided to keep the vessel at 350 °C. Interesting compounds organic will still form – only in smaller amounts.
The ammonia reaction above (the first equation) is actually an equilibrium reaction. That means that the reactants are never completely used up, and the yield is not 100%.
Recall from Le Châtelier’s principle that removing product from an equilibrium reaction causes the position of equilibrium to shift to the right, forming more product. This is because:
“If an equilibrium system is subjected to a change, the system will adjust itself to partially oppose the effect of the change.” – Le Châtelier’s principle
There are three reactions that will remove ammonia from our vessel while it’s being produced, and I’ve put all three of these into the simulation. One of these is the reverse of the reaction above (producing hydrogen and nitrogen gases) and the other two are described below. Let’s take a look at those other two reactions.
With what will the ammonia react in our vessel?
Ammonia can undergo the following reactions with the other things in our vessel**
**The ammonia does react with methane and beryllium as well, but only at temperatures of 1200 °C and 600 °C, respectively.
Two compounds will be formed: lithium amide and borazine. Lithium amide reacts with nothing else in the vessel, so the reaction chain stops there. Borazine, on the other hand, is much more interesting.
We’ve made borazine!
Borazine is a colourless liquid at room at temperature. It boils at 53 °C and has a structure that resembles that of benzene.
Because of the electronegativity difference of about 1.0 between the B and N atoms in the ring, borazine has a mesomer structure:
Like benzene, there is partial delocalisation of the lone pair of electrons on the nitrogen atoms.
Borazine polymerises into polyborazine!
Fascinatingly, borazine polymerises into polyborazine at temperatures above 70 °C, releasing an equal number of moles of hydrogen gas. Polyborazine isn’t particularly well-understood or well-documented, but one recent paper suggested it might play a role in the creation of potential ceramics such as boron carbonitrides. Borazine can also be used as a precursor to grow boron nitride thin films on surfaces, such as the nanomesh structure which is formed on rhodium.
Like several of the other compounds we’ve created in our Periodic Table Smoothie, polyborazine has also been proposed as a hydrogen storage medium for hydrogen cars, whereby polyborazine utilises a “single pot” process for digestion and reduction to recreate ammonia borane.
The hydrogen released during the polymerisation process will then react further with a little bit of the remaining nitrogen to produce a little more NH3(g) – but not much. Recall from earlier that the ammonia reaction is an equilibrium one, and the yield of NH3(g) at pressures under 30 atmospheres is very low. Pressure in our vessel is still only around 7 atmospheres.
Once polymerised, this would form about 12 grams of polyborazine:
As far as I’m aware, no further reactions will take place in the vessel this week.
Conclusion after adding 1.00 mole of nitrogen gas
Amount in mol
Pressure: 891 kPa (higher than before due to the addition of nitrogen gas) Temperature: 350 °C (vessel is still being maintained at constant temperature)
Next week, we’ll add a mole of oxygen gas to the vessel. Warning: it might explode.
Stock, Alfred and Erich Pohland. “Borwasserstoffe, VIII. Zur Kenntnis Des B 2 H 6 Und Des B 5 H 11”. Berichte der deutschen chemischen Gesellschaft (A and B Series) 59.9 (1926): 2210-2215. Web.
Today, we’re going to add 1.00 mole of carbon to our vessel. After adding boron last week, we left our vessel locked at 350 °C and with a pressure of 638 kPa. These reactions are taking place at 350 °C and constant volume (exactly 10 litres). Pressure inside the vessel will therefore change over time.
Allotropes of carbon
Carbon has various allotropes (structural arrangements of an element). Diamond is extremely strong and highly unreactive, while graphite is soft and brittle. The differences are all due to the type of bonding between carbon atoms. In diamond, carbon atoms are bonded by four strong covalent bonds with the surrounding atoms in a strong, hard three-dimensional ‘network lattice’. Graphite owes its softness and brittleness to the fact that its carbon atoms are bonded by only three strong covalent bonds in a two-dimensional ‘layer lattice’. Individual layers are very strong, but the layers can be separated by just the slightest disturbance. Touching graphite lightly onto paper will remove layers of carbon atoms and place them onto the page (such as in a pencil). Using a diamond the same way would likely tear the paper instead.
For this reason, I’m going to put graphite into the vessel instead of diamond. Diamond is so strong and inert that it’s unlikely to do any interesting chemistry in our experiment. Graphite, on the other hand, will.
The following seven chemical reactions will take place after adding carbon (graphite) powder
As soon as the carbon powder enters the vessel, it will begin to react with the following three species as follows:
The ethyne produced in the third reaction will then react with any lithium and beryllium remaining in the vessel as follows:
The hydrogen gas produced by the above two reactions will then react with lithium and carbon (if there’s any left) as follows:
These reactions have the potential to all occur at the same time. Tracking them properly would require calculus and lots of kinetics data including the activation energy of each reaction and the rate constant for each equation. Quick searches on the National Chemical Kinetics Database yields no results for most of these equations, which means we won’t be able to use a computer model to calculate exact quantities of each product. Instead, I’m going to run a computer simulation using Excel that makes the following three assumptions:
all these reactions occur at the same rate;
all these reactions are first-order with respect to the limiting reagent;
all these reactions are zeroth-order with respect to reagents in excess.
The results will be a close approximation of reality – they’ll be as close to reality as we can get with the data that’s available.
Here are the results of the simulation
Here’s a graph of the simulation running for 24 steps. Exactly one mole of carbon powder is added at step 5.
Summary of results
The results are incredible! We’ve made ethyne and methane, both of which have the potential to do some really interesting chemistry later on. I’m hoping that we can make some more complex organic molecules after nitrogen and oxygen are added – maybe even aminoethane – let’s see.
Hydrogen has also re-formed. I’m hoping that this gas lingers for long enough to react with our next element, nitrogen: we might end up making ammonia, NH3(g).
You may have noticed that I removed the “boron-lithium system” from the vessel. The 0.178 moles we created are now stored separately and will not be allowed to react any further. With such little literature about the reactivity of B3Li, it’s impossible to predict what compounds it’ll form later on. B3Li is so rare that doesn’t even have a Wikipedia page.
Here’s what’s present in the vessel after adding carbon
Moles present after 500 ‘steps’
We also have 0.178 moles of B3Li stored separately in another vessel.
Next week, we’ll add nitrogen and see what happens.
Boron is a metalloid: an intermediate between the metals and non-metals. It exists in many polymorphs (different crystal lattice structures), some of which exhibit more metallic character than others. Metallic boron is non-toxic, extremely hard and has a very high melting point: only 11 elements have a higher melting point than boron.
British scientist Sir Humphrey Davy described boron thus:
“[Boron is] of the darkest shades of olive. It is opake[sic], very friable, and its powder does not scratch glass. If heated in the atmosphere, it takes fire at a temperature below the boiling point of olive oil, and burns with a red light and with scintillations like charcoal” – Sir Humphrey Davy in 1809
Before we add the 1.00 mol of boron into our reaction vessel, we need to recall what’s already in there from our experiments so far:
H2(g): 0.70 mol
He(g): 1.00 mol
Li(s): 0.40 mol
LiH(s): 0.60 mol
Be(s): 1.00 mol
The temperature of our vessel is 99 °C and the pressure of the gaseous phase is 525.5 kPa.
Now, let’s add our 1.00 mol of boron powder.
Which reactions take place?
Boron reacts with hydrogen gas to produce a colourless gas called borane, BH3(g), according to the following equation:
Boron also reacts with lithium in very complex ways. If we heat the vessel up to 350 °C, we’d expect to see the formation of a boron-lithium system with chemical formula B3Li according to this equation:
Notice that now we’ve heated up our vessel to 350 °C to allow this reaction to happen, the lithium at the bottom of the vessel has melted.
Boron reacts with lithium hydride as well, but only at temperatures around 688 °C. With our vessel’s temperature set at 350 °C, we won’t observe this particular reaction in our experiment.
Some allotropes of boron – in particular, the alpha allotrope that was discovered in 1958 – is capable of reacting with beryllium to form BeB12. Because we’re using beryllium powder, which has semi-random symmetry, we won’t see any BeB12 forming in our vessel. Alpha-boron only exists at pressures higher than around 3500 kPa. At our moderate pressure of only 525.5 kPa, powdered (semi-random) boron will prevail and no BeB12 will form.
For simplicity’s sake, let’s assume that the two reactions above take place with equal preference.
Boron powder reacts with hydrogen gas
Let’s do an ice table to find out how much borane we make.
A quick n/ratio calculation shows us that the hydrogen gas is limiting in this reaction:
We can expect all of the hydrogen gas to react with the boron powder.
units are mol
Borane is very unstable as BH3, and it would probably dimerise into B2H6(g). This is still a gas at 350 °C and is much more stable than BH3. For the rest of this experiment we’ll assume that our 0.466 mol of BH3 has dimerised completely into 0.233 mol of B2H6.
Boron powder reacts with lithium
With the molar ratios present in our vessel, at 350 °C, we’d expect to witness the formation of a boron-lithium system, with chemical formula B3Li.
A quick n/ratio calculation shows that in this reaction, the boron powder is limiting.
All of the remaining boron therefore reacts with lithium. To calculate exactly how much B3Li we’ve created, let’s do another ice table:
units are mol
What’s in our vessel after adding boron?
We have the following gas mixture in our vessel:
Helium gas, He(g): 1.00 mol
Helium is an inert noble gas that will probably remain in the vessel until the end of the experiment. It’s used in party balloons.
Borane gas, B2H6(g): 0.233 mol
We made this today. Borane is used in the synthesis of organic chemicals via a process called hydroboration. An example of hydroboration is shown below.
At the bottom of the vessel, there’s a sludge, which contains the following liquids and solids:
Molten lithium, Li(l): 0.22 mol
Lithium is used in the production of ceramics, batteries, grease, pharmaceuticals and many other applications. We’ve got 0.22 moles of lithium, which is about 1.5 grams.
Beryllium powder, Be(s): 1.00 mol
Beryllium is used as an alloying agent in producing beryllium copper, which is used in springs, electrical contacts, spot-welding electrodes, and non-sparking tools.
Lithium hydride, LiH(s): 0.60 mol
Lithium hydride is used in shielding nuclear reactors and also has the potential to store hydrogen gas in vehicles. Lithium hydride is highly reactive with water.
Boron-lithium system, B3Li(s): 0.178 mol
We made this today… but what is it? Not much is known about this compound – in fact, it doesn’t even have a name other than “boron-lithium system, B3Li”. It’ll probably decompose eventually in our experiment – maybe when we alter the pressure or temperature of the vessel at some later stage. We’ll need to keep an eye on this one.
The original H2(g) and B(s) have been reacted completely in our experiment.
What’s the pressure in our vessel now?
At the end of our reaction, the temperature of our vessel is still set at 350 °C and the pressure of the gaseous phase inside the vessel can be calculated to be a moderate 638 kPa as follows:
*It should also be noted that some evidence exists for a reaction between LiH and BH3, forming Li(BH4). The reaction seems to take place stepwise with increasing temperature. A quick read of this paper suggests that in our vessel, which is at 350 °C, any Li(BH4) formed would actually break back down into boron powder and hydrogen gas, which would in turn react with each other and with lithium metal to form BH3 and LiH again. The net result would be a negligible net gain of LiH and a negligible net loss of boron powder. We will continue calculating this Periodic Table Smoothie under the assumption that if any Li(BH4) forms, it breaks down before we add the next element, and the overall effect on our system is negligible.
**Li(BH4) is an interesting compound: it’s been touted as a potential means of storing hydrogen gas in vehicles – it’s safer and releases hydrogen more readily than LiH, which was mentioned above.
Next week, we’ll add element number 6, carbon, and see what happens.
Li(s): 0.40 mol (still solid: it melts at 180.5 degrees)
LiH(s): 0.60 mol
Pressure = 525.5 kPa
Temperature = 99°C
Beryllium doesn’t react with any of the things in the vessel: H2(g), He(g), Li(s) or LiH(s). My one mole of beryllium powder (which would cost me over $70) would just sit at the bottom of the vessel doing nothing.
With not much else to write about in the Periodic Table Smoothie this week, it might be a good idea to calculate how much this Periodic Table Smoothie would have cost in real life.