Redox can be a confusing topic for VCE Chemistry students. It’s also taught right at the end of the year, when students are tired and some teachers are rushing their lessons so they can finish the course before the end of Term 3. Student motivation levels are at their lowest time of the year, which means that students often finish the course with an incomplete understanding of Redox.
Fortunately, there are six universal principles that are always true in Redox no matter what type of cell is being studied.
First, here’s a reminder of the types of cells you need to have studied in this course.
Primary (can’t be recharged)
Secondary (can be recharged)
Fuel Cells (reactants are supplied continuously)
Electroplating Cells (no overall reaction)
Electrolytic Cells (non-spontaneous reaction)
Commercial Cells (usually molten electrolytes)
Recharge reaction of a secondary cell (non-spontaneous)
Now, here are the six universal Redox principles.
1. The strongest oxidant at the cathode reacts with the strongest reductant at the anode (SOC SRA)
To predict which species will react with each other, circle all the species present at the cathode on the electrochemical series. The highest species on the left will always react. Now, circle all the species present at the anode… the lowest species on the right will react.
2. The half-reaction with the highest E° value is always positive
In all cells, the half-equation with the highest electrode potential (also called ‘reduction potential’ or E° value) always occurs at the positive electrode. Similarly, the half-equation with the lowest electrode potential (E°) will always occurs at the negative electrode.
3. OIL RIG
Oxidation is loss of electrons. Reduction is gain of electrons.
4. ←AN OIL RIG CAT→
Anode reaction (oxidation reaction) is whichever reaction is happening to the left in the electrochemical series.
Cathode reaction (reduction reaction) is whichever reaction is happening to the right in the electrochemical series.
5. Electrons always flow in this order (RACO)
Reductant → anode → cathode → oxidant
6. In the internal circuit, cations always flow to the cathode, and anions always flow to the anode.
The internal circuit might be an electrolyte or a salt bridge that contains soluble weak oxidants and reductants such as KNO3(aq) (potassium nitrate). Either way:
cations always flow to the cathode; and
anions always flow to the anode.
Keep practicing redox questions by completing past papers, Checkpoints and Lisachem questions. If you need more help, contact me via the Get a Tutor button in the site’s menu bar. Students learn much faster with a tutor than on their own.
We all remember the endless ‘cells’ questions at the end of the 2014 Chemistry exam. Less memorable was that the 2013 examination awarded a similar number of marks for ‘cells’ knowledge. Exams that test knowledge of these last two chapters in the course (Galvanic Cells and Electrolytic Cells) separate goodstudents from great students because these topics are taught at the end of the course when students are getting tired and teachers are rushing to finish the course before trial examinations and the Term 3 holidays. Only the most diligent students go out of their way to get a complete understanding of these topics at this stage in the year – and they’re the ones who benefit from this type of exam.
Interestingly, in 2013 and 2014, 33% of the marks in the VCE Chemistry examination were awarded for knowledge of just four of the textbook’s 28 chapters. Therefore, if you’re short of time, focus your efforts on these four chapters (28, 27, 16 and 12) before working on the rest.
“Based on past examinations, students should focus their revision on Electrolysis (28), Galvanic Cells (27), Equilibrium (16) and Biomolecules (12) before working on the rest…”
While the structure of past examinations provide no guarantees about future examinations, it’s still reasonable to expect that the top 5 subjects will remain mostly the same in 2015 as in previous years.
Correlation of the total number of marks awarded per chapter is moderate with R² = 0.48 for 2013 and 2014.
Consider getting a home tutor who can answer your questions and explain difficult concepts to you. Students learn much faster with a tutor than on their own.
Track your progress in VCE Chemistry with this A3 size progress tracker. Cross out or colour in each box as you complete it, and write your scores in . Start at the bottom (highlighted) and work your way upwards.
A ‘minimum expected level of examination preparation’ of 26 examination papers is labelled on the chart. Write your percentage scores in each of the boxes as you mark each paper. When you’re achieving past/practice examination scores concordantly above 90%, you’re ready to sit the VCE Chemistry examination.
1. Develop excellent study skills. Cultivate ideal study habits such as waking up early, reading your notes before school, doing all homework on time and studying even when there’s no homework set.
2. Stay committed and know what you want and WHY. People who know why they do what they do are far more likely to persist and put in the huge number of hours required to excel at that particular skill. All successful people were driven by a higher. Find your why and you’ll feel more motivated to study VCE.
3. Keep motivation levels high and consistent throughout the year. Remind yourself constantly why you’re studying the VCE subjcets you’ve chosen.
4. Do not “over-indulge” in VCE tutoring. Your tutors and teachers can only take you so far. The highest-achieving students are those who are self-motivated: they push themselves and study even when nobody asked them to. Become self-motivated and use your tutoring time wisely to maximise your performance in VCE exams.
2. There are two things you need to do: make great notes and do practice questions.
3. Build on your notes from external sources (other people’s notes and the textbook)
4. Mark your questions – or get them marked! Akhil says that while it’s an excellent learning exercise to practice marking questions by yourself, it’s also necessary to get your practice papers and Checkpoints questions marked by a teacher or tutor because they’ll be more vigilant with sticking to the marking scheme and can pick up slight errors in wording that are easy to miss if you mark your own work.
RTQ! This is one of the most common sources of errors in Chemistry examinations. When I sat 2014’s VCE Chemistry examination, I lost 5 marks in the paper for not reading the question! Your teachers will have told you to ‘read the question’ or ‘RTQ’ as well.
Task word errors can be avoided in two ways. First, learn the exact meanings of each task word. This is particularly important for EAL Chemistry students. Second, highlight the task words in a question (just as you would highlight the important information in a complicated titration question).
For example: “Explain how the different intermolecular forces in butane and butan-1-ol give these two compounds different boiling points. 3 marks”
In your answer, you will need to explain the effect of intermolecular forces. This means you’ll need to write why the butan-1-ol forms hydrogen bonds (due to the polar nature of the hydroxyl group) whereas butane forms only dispersion forces with its surrounding molecules (due to the non-polar nature of the molecule). You’ll also need to make some kind of comparison (which is hinted at by the word, ‘different’) in order to get all 3 marks.
Example 3-mark answer: “Butan-1-ol forms intermolecular hydrogen bonds with the surrounding molecules due to the polar nature of the hydroxyl group (O-H bond). Butane forms only dispersion forces with its surrounding molecules due to the non-polar nature of the molecule. Hydrogen bonds are stronger than dispersion forces and thus require more energy to break. This results in a higher boiling point for butan-1-ol than for butane”.
One mark would be awarded for each of:
Explaining the intermolecular bonding of butan-1-ol
Explaining the intermolecular bonding of butane
Comparing the relative strengths of the two and relating this to boiling points
In a 2-mark answer, the student might omit the comparison step:
Example 2-mark answer: “Butan-1-ol forms intermolecular hydrogen bonds with the surrounding molecules due to the polar nature of the hydroxyl group (O-H bond). Butane forms only dispersion forces with its surrounding molecules due to the non-polar nature of the molecule.”
In a 1-mark answer, the student might only mention one of the two molecules, or might only make a comparison without explaining whythese two compounds display different types of intermolecular forces.
Example 1-mark answer: “Hydrogen bonds formed by butan-1-ol are stronger than dispersion forces formed by butane and thus require more energy to break. This results in a higher boiling point for butan-1-ol than for butane”.
In that latter example, the student didn’t explain the reasons for the differences in intermolecular bonding – they merely stated them.
Write the value of a number (include equations)
Write the similarities and differences between
Write arguments for and against
Write the exact meaning of
Write details about (a thing or a process)
Write reasons for and against
Write the differences between two or more things
Write details to give the reader an understanding of
Write (sometimes by doing calculations)
Write which one
Write something and draw a labelled diagram as well
Write which one (usually on a given diagram)
Write a list
Write a summary
Write a reason for a phenomenon
To what extent
Write whether a reaction is complete (→) or incomplete (↔).
Watch task words in the examination… and make sure you answer the question!
Memories and connections are some of the most valuable things you’ll take with you from Year 12. Keep in touch with as many people as possible both officially (using alumni networks) and unofficially (using social media). People move in different directions after graduation and you’ll be surprised at how your friendships evolve, too: classmates who were mere acquaintances during school might become very close friends in five years’ time. Keep in touch with all your classmates to make sure you don’t miss out on these future business connections, too. You might even meet again one day sitting opposite each other at a job interview!
Remember that your ATAR is only a means to a much more meaningful goal: it’s the key to a university course of your choice. Strive for an ATAR that’s high enough: there’s no need to stess yourself out by aiming for a ‘perfect’ score of 99.95. Your ATAR is like a disposable key: it gets you into university but doesn’t help you while you’re there. Nobody asked me what my A-level results were throughout my undergraduate years at Cambridge. High-school results simply weren’t important.
3) A Relentless Work Ethic
You’ve worked harder in Year 12 than you’ve ever worked in your life. If you want to be successful, you’ll have to maintain this level of hard work – or even increase it – to accomplish your goals in life. You’ve learned the difficult way that in Year 12, going to school and doing all the required homework isn’t enough. You’ve figured out in Year 12 that you have to spend hours reading the textbook by yourself, doing practice question sets that aren’t on the course, and making summary notes that your teacher will probably never see in order to get a high grade.
The relentless work ethic you’ve garnered will help you to conquer bigger obstacles in the years that follow. Give every major event in your life at least as much passion, dedication and preparation that you gave to your VCE examinations and you’ll be sufficiently prepared for the challenges that await you in the future. VCE is pre-season training for life.
Is there anything I’ve missed from this list? Is an ATAR more than just a “key to a university course”? Let us know in the comments section below.
As a Chemistry teacher, my initial reaction to the enormous explosions at a hazardous chemicals storage facility in Tianjin, China this week was a need to find out what exploded and why. As soon as the news broke, I started following #Tianjin on Twitter and getting alerts from Google News. Here’s what I’ve learned about the Chemistry behind these two fatal blasts. We know there were several dangerous chemicals on site. We also know that firefighters were present at the facility putting out a fire before the first explosion. The second explosion was much larger than the first, with the two blasts measuring the equivalent of 3 and 21 tons of TNT, respectively. The second, larger blast was so powerful that it caused a magnitude 2.9 earthquake in the surrounding area. For a surface explosion to cause a measurable earthquake is rare.
Here’s my understanding of what happened.
Stage 1: Fire
An unknown substance caught fire inside one of the storage containers at the facility. Firefighters arrived at the scene to douse the flames with water.
Stage 2: Water touches calcium carbide, producing acetylene gas
Calcium carbide, CaC2(s), is an unstable compound that’s used in the production of acetylene (ethyne) and also in steelmaking. When water (or moist air) touches calcium carbide, it fizzes gently, releasing acetylene gas, C2H2(g), which, when mixed appropriately with air, explodes upon ignition. The reaction above is only slightly exothermic, and the ethyne gas released is colourless and odourless: it’s possible that the firefighters didn’t even notice that the gas was being produced.
Stage 3: Flames ignite the acetylene gas, causing the first explosion
After the ethyne had mixed sufficiently with the surrounding air, one part of this explosive gas mixture was ignited by the pre-existing flames, causing the first explosion.
Eyewitness reports have estimated this first explosion to be equivalent to 3 tons of TNT, which equates to 12.5 million kilojoules of energy. Using n = E/ΔH, we find that around 9662 moles of ethyne appears to have exploded. Using V = n×VM, we can calculate that at 25°C and 1 atm of pressure, that explosive gas would have occupied a volume of 236719 litres. Using r = (3V÷4π)1/3, we can approximate the ethyne gas to have occupied a sphere 76 metres in diameter, which is (very approximately) consistent with what we’ve seen in the video footage.
Interestingly, we can do a simple stoichiometric calculation using m = n×Mr and calculate the initial mass of calcium carbide that decomposed: 9662 × 64.1 = 619 kilograms. At a density of 2.22 g/cm3, those 619 kilograms would have occupied 279 litres in powdered form: this is about the same size as three large luggage cases.
A quick search on Chinese wholesale directory Alibaba.com shows that very few companies offer calcium carbide in such small quantities, which might help narrow down which company was responsible. Interestingly, the raw material for that first explosion was worth a mere US$400 at 2015 wholesale prices… but the consequential damage was far more costly.
Stage 4: High temperatures caused nearby ammonium nitrate to detonate at >240°C, causing the second explosion
Temperatures of over 3000°C were generated by the combustion of the ethyne in stage 3. The immense heat from that initial fireball heated the surrounding containers to above 240°C, which initiated a runaway decomposition reaction of ammonium nitrate, NH4NO3(s), which was stored nearby. The reaction is shown below.
The products of these two explosions are calcium hydroxide, carbon dioxide, water vapour, nitrogen and oxygen, which pose zero risk to nearby residents. However, the main concern now is that other (non-flammable) hazardous chemicals such as sodium cyanide, NaCN(s), might have been tossed into the air following the first two explosions. Residents living within 3 kilometres of the blast site have been evacuated as a precaution.
A recent report by PriceWaterhouseCooper predicted that 44% (5.1 million) of the jobs that exist in Australia today are at risk of ‘digital disruption’ by 2035. PwC predicts that computerisation and technology will not only create new jobs in the next 20 years but will ultimately supersede much of the existing workforce as well.
In order to realise our full potential, Australia needs an appropriately skilled workforce; a workforce fit for the future. PwC has concluded that expanding our STEM industries (Science, Technology, Engineering and Mathematics) would maximise economic outcomes for Australia in the next few decades.
The Australian economy has benefited greatly from economic reforms and from increasing demand for natural resources, mostly from China, which drove most of Australia’s growth in the early 2000s. At the same time, the PwC report says, economic growth from productivity has halved and Australia needs to develop a strong STEM foundation to guarantee economic growth after the current commodity boom has finished.
While it’s important to choose a future-proof career in one of the fields above, the benefits of doing so extend far beyond the individual level. PwC has predicted that Australia could gain a $57 billion economic boost between 2015 and 2035 if it switched just 1% of its workforce into STEM occupations. Australia’s prosperity in the next few decades appears to be highly dependent on our nation’s commitment to STEM.
Conclusion: schools and STEM businesses need to do more outreach
“Business also has the opportunity to better connect with students. This can be done by profiling emerging STEM careers, talking about workforce needs, offering workforce and internship experiences and breaking down the stereotypes and barriers that still remain today. It’s not new, but scope exists for a much more coordinated approach to engaging with the potential STEM workforce.”
I’m excited to say that my wife and I are expecting our first baby in November: we’re expecting her to be born shortly after the VCE Chemistry examination! Like most new parents, I’ve been pondering baby names in the last few weeks. In particular, I’ve been looking for a girl’s name that’s traditional, popular and sounds intelligent.
The first two criteria are easy to satisfy: we can look to the Royal Family for traditional names; and the most popular baby names of 2015 are just one Google search away. However, the third criterion is a bit more difficult: what’s the most intelligent girls’ name? With this question in mind, I set out to find the most intelligent first name in Victoria based on empirical evidence from three publicly available databases.
Method: combine three public databases
I downloaded the list of 40+ VCE study scores for 2014 from the Herald Sun’s website. I cleaned the database using Microsoft Excel and obtained a neat, searchable list of 13,478 students and their VCE results that looked like this:
I removed outliers by deleting all the rare names from the list. Only names with 5 or more high achievers (40+) were included in the final analyses. Admittedly, this removed most Chinese students from the database because they have very unique first names, but I’ll expand on the implications of this later.
I then merged this database with the list of surnames and their prevalences that I obtained from IP Australia, and a similar list of first names from the NSW Government website. Now, I could query my database with interesting questions such as, “Which first name got the highest average ATAR in 2014?” and “Which surnames had the highest proportion of 40+ study scores?” The results were fascinating, and will be of some help when deciding a name for a newborn baby.
Table 1: Students called “Victor” achieved the highest mean ATAR in 2014
The ATARs of students called Victor were far higher than the ATARs of students with any other first name. (Is that because we live in Victoria?) I’ve coloured the names blue, pink or green to represent whether the names are male, female or both.
Table 2: Hilary, Judy and Derek had the highest proportion of 40+ study scores in 2014
I added some more columns to the spreadsheet to estimate what percentage of students born with those 50 first names in 1997 in Victoria achieved a 40+ study score in at least one subject. According to my estimates, every student called Hilary, Judy or Derek achieved at least one study score of 40 or above in their 2014 VCE examinations. Correct me if I’m wrong.
Where are all the Asian names? I mentioned earlier that I removed all the rare names to eliminate outliers from the database. (This is standard practice.) The vast Chinese character set gives rise to literally millions of possible first names, which means that many Chinese students have unique first names and most of them were therefore excluded from my previous analysis. For a truer reflection of the influence of Chinese-background students in VCE, we need to look at students’ surnames instead.
“…every student called Hilary, Judy or Derek achieved at least one study score of 40 or above in their 2014 VCE examinations.”
Table 3: Students with the surname “D’Souza” achieved the highest mean ATAR in 2014
I re-ordered the list of 13,478 students to show the mean ATAR for each surname. Surprisingly, the highest achieving surname was D’Souza, which was originally Portuguese but is now found worldwide. According to Wikipedia, “A prominent family carrying the spelling de Sousa emigrated from Portugal to Goa during mid 1956 before leaving to Hong Kong. This was followed by a third relocation in the mid 1960s, where they now reside in Melbourne, Australia. The family donated their property in Hong Kong to Franciscan nuns.” Their success in Melbourne continues to this day.
Chinese surnames dominated the rest of the top 50. The second-place surname, Chin, for example, comes from Qin Shi Huang, the first ever Emperor of China. He was born in 269 BC and is still regarded as one of the boldest emperors in Chinese history. It’s also believed that the English name for ‘China’ was derived from Emperor Qin Shi Huang’s name.
A few English, Korean, Irish and Vietnamese surnames also made it into the top 50. Kennedy was 273rd out of 379 surnames.
Table 4: Chinese surnames dominate 40+ study scores
An ATAR is an aggregate score of 4 to 6 subjects including English and (usually) Maths, and thus provides an indication of how well-rounded a student is academically. Next, instead of finding lists of well-rounded students, I wanted to find out which students excelled in just one or more subject. I chose study scores of 40 or above as a benchmark. I then divided the number of students with each surname who achieved at least one study score of 40+ by the number of people in Victoria who had that surname. The result is a fairer indication of which students excelled in one or more area, but didn’t necessarily excel in all subjects. The results were fascinating!
Three Sri Lankan surnames and 47 Chinese surnames dominated the top 50. Interestingly, an estimated 23% and 22% of students surnamed Jayasinghe and Ranasinghe achieved a study score of 40+, respectively, which is many times higher than the VCE student population as a whole.
You perform much better when you warm up before strenuous physical exercise. The same applies to Chemistry, too: if you warm up your brain before coming to class, you’ll feel more alert during the lesson and you’ll learn heaps more as a result. Here are some of the benefits of warming up before coming to class.
The best warm-up: read the textbook before class
One of the best warm-up drills is to read the relevant textbook section before going to class. Try to pre-read your textbook section no more than 24 hours before the lesson takes place; for example, during breakfast. Even though not all of the information made sense to me during this initial pre-read, it will at least make you understand the lectures a little better. Knowing key definitions before the lecture begins is crucial to understanding much more of what the lecturer is saying. You’ll also walk into the classroom with questions already in your head, ready to ask. This impresses the teacher and your classmates.
FOCUS during the lesson and make Cornell Noteswhile the teacher is talking. In addition to writing down key information the teacher tells you and writes on the board, write down any questions you might want to ask them later. Cornell Notes are an excellent way of doing this: you put your question in the Cue Column and leave the right part blank: you can fill this in with your answer at a later date (or by asking the teacher at the end of the lesson). Trying to formulate questions to pose to the teacher while you listen to a lesson is a good way of committing the information being learned to your long-term memory. This works because you’re invoking higher-order thought processes and learning more actively.
With this in mind, review your notes within 24 hours of the lesson and again at regular intervals afterwards. You’ll need to continually improve your notes after you’ve made them: answer questions you left blank in the Cue Column, insert definitions to confusing words, and label the diagrams you left blank during the lesson. Stay ahead of that forgetting curve!
Don’t have time to pre-read the textbook? Nonsense!
Skim-reading your textbook section over breakfast takes about 10 minutes, and reading and highlighting key definitions takes just another 2 minutes. By investing 12 minutes of time before class, you’ll learn more during the lesson and waste less time afterwards trying to decode what the teacher was saying. You’ll also have the confidence and the ability to answer to more questions in class. Your peers will start to see you as the person who always knows the answer to the teacher’s questions, which gives you a self-fulfilling reputation for being ‘smart’.
Reviewing and fleshing our your notes after class doesn’t take long, either. The exact time depends on the difficulty of the topic. Remember that the time you invest doing the above three things will pay off during the examination. If you don’t have time to do these three things, then make time. Get reading!
How do you warm up before class? What study habits help you the most? Share your ideas in the comments section below.
You’ve got 100 days until your English examination and full-time revision should begin from today.
How to Make a Revision Timetable
First, print my 2015 wall calendar in A3 size or larger. The left, middle and right of each day-box represents each of three study sessions:
Morning session: 8am to 12pm (make a dot to the left)
Afternoon session: 1pm to 5pm (make a dot in the middle)
Evening session: 6pm to 9:30pm (make a dot to the right)
Next, use coloured stickers from Officeworks(or coloured markers) to label your examinations. Use a different colour for each subject. Working backwards from those examinations, put more stickers on the chart to denote which subjects you’ll study in each study session.
Rules when filling your timetable:
Plan 100 revision sessions in the 100 days before your first examination
Try not to plan revision sessions on school days – save that time for homework!
Adjust the number of sessions you will have for each subject: you might want to focus more on some subjects than on others, or prepare for them all equally. It’s up to you.
Revise for 12 sessions each week that you’re not in school
Revise for no more than two sessions in a day
Avoid the evening session when possible.
Use your free time to relax or get some exercise.
You may move a study session but you are not allowed to cancel it
Make Your Own Revision Timetable
This strategy worked extraordinarily well for me during my A-level studies. I studied this much (48 hours per week) and achieved an equivalent ATAR of over 99. What’s your revision strategy? Leave your ideas in the comments section below.