Category : Teaching and learning

Comparison between Galvanic and Electrolytic Cell

Mr Khemistry

Comparison between galvanic and electrolytic cell table

Students tend to get mixed up between the two types of electrochemical cells. This table will illustrate the comparison between galvanic and electrolytic cell.

A useful acronym, P.A.N.I.C. for electrolytic cell polarity (Positive is Anode Negative is Cathode). Then just remember polarity is reversed for galvanic cell.

If you found this useful, share it with your friends!

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Born Haber Level Diagram

Mr Khemistry

Born Haber Level Diagram

Born Haber Level Diagram

Always start your cycle at datum line, i.e. at zero enthalpy. Tip: You may combine the ionisation energies for Fe or for other metals.
Multiple electron affinities can also be combined.

Take note that for energy level diagram, you will have to show the ionized electrons from Fe. When you use bond energy instead of enthalpy of atomisation, you will need to multiply by the correct coefficient. Lastly, don’t forget to put your state symbols! 🙂

Hope this has been useful for you, if you wish to learn how to draw the diagram using energy cycle, go here.

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Born Haber Cycle

Mr Khemistry

Born Haber Cycle

Born Haber Cycle Diagram

Born Haber Cycle

Using the acronym F.A.I.L. where F stands for enthalpy change of formation of the ionic compound, A stands for atomisation of the constituent elements and I stands for ionisation of cation and anion and L stands for Lattice Energy.

We have four major components and this energy cycle is easy to draw with no worries about which species having a higher energy level. There is no need to include electrons as they are immediately used to form the anion.

Hope this has been useful to you! Share it with your friends if it has helped you 🙂

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Free Radical Substitution MCQ Analysis

Mr Khemistry

Free Radical Substitution MCQ

This MCQ is about free radical substitution, be sure to read up before looking at the solution!

Which of the following is a possible product in the reaction between cyclohexane and bromine with UV light?

Free Radical Substitution

Analysis:  The common answer dicyclohexane isn’t one of the given options. So we will have to choose from the above options.








A: Note that this option has a total of 14 carbon atoms, not 18. The cyclohexane radicals all has 6 carbon atoms so the products should be in multiples of 6.

B: Similarly, this option has a total of 13 carbon atoms, not 18.

C: This option has 16 carbon atoms.

D: This option has 18 carbon atoms and is the correct answer! Do remember that cyclohexane can undergo multiple abstraction of H atom by the bromine radical.

If you liked this question, share it with your friends and see if they know how to do it! If you need help for organic chemistry, consider signing up for our weekly classes. We have challenging weekly Organic multiple choice questions just like this one for your practice.

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Writing it down

Mr Khemistry

Thoughts disentangle themselves when they pass through the lips and fingertips – Dawson Trotman

There’s much value in writing down what we are teaching. This past week, i’ve had feedback from students telling me they understand the lessons much better. 

The secret formula is to actually write down what i’m saying. Not every single word, but the important structures (i’m teaching organic chemistry at the moment).

And then to draw arrows to show the linkage between structures, use different coloured ink to highlight changes in functional group. For example,

halogenoalkane concept map

This simple action of writing down the concepts is easy to say but hard to do. It is always easier to rattle off what we are thinking because it’s faster. But spoken words floats into the air and dissipates. Before the students has time to process what structures you are referring to, you would already be going on to the reactions. Reagents and conditions. Isomerism. Mechanisms. There is so much going on, on so many levels, that students might get lost at any one of those levels.

For example, a quick check might have intended to assess whether they know how to process nucleophilic substitution mechanism for acyl chlorides. But students don’t even know what’s the structure of ethanoyl chloride to start! Most of the time, in a big JC lecture theatre, they will just pretend to be busy while just waiting for you to flash the answers. This really defeats the purpose of the quick check.

The point is, you’re the only one who has thought it through and have a clear image in your mind. Students are trying to listen to what you’re saying but most of the time they get lost when you refer to an imaginary structure. Then once lost, they tend to space out since whatever else you’re saying makes no sense to them. I always had to pause and ask myself, “Am i rushing to cover the syllabus or am i making sure everyone understands what i’m teaching?”

Writing down your thoughts and speech on the board will allow them to follow you, so even if they lost you half-way, they can easily pick up from where they left off. I can’t emphasize this point enough, WRITE IT DOWN. With different colours for them to know what has changed, what’s important etc.

Teaching Organic Chemistry

For me especially, it is easy to just project the answers on the screen and let them copy it down. But they have no idea how to work out the answers from ground zero, what’s the thought process. Increasingly, i see that if i lead them step by step, by writing it out, they will understand so much better. 

Whittling the lesson down to just 1 or 2 main ideas makes it easier for absorption. Like zipping a big chunky file into a manageable size allows it to be downloaded faster.

I’m glad that my classroom has this white wall which i can use to write on. Ample space to spread out structures and mechanisms clearly.

Come join us to see how clear our explanations are! 🙂 WhatsApp us to reserve your seat today!

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Thinking skill – what is more important, content or thinking skill?

Mr Khemistry

Thinking skill – what is more important, content or thinking skill?

Have you seriously thought about this question? If not, you need to. At ‘A’ levels, we need to not just learn about the content. Notice i did not say, don’t learn the content.

Students at Advanced level need to be able to think and apply their knowledge. A lot of people assumed that they know how to think or are living their lives thoughtfully. The truth is, many are not. 

Henry Ford said, “Thinking is the hardest work there is, which is probably the reason why so few engage in it.”

I’ve had an incident recently in the wee hours of the morning when my toddler woke up crying for milk. I went to make it while my wife attended to him. But lo, i realised my wife had set the air pot to boil and i was not able to dispense the hot water to make the milk. I stood there tapping my fingers and murmuring how slow the water took to boil. 

My wife walked in just at that moment when i was murmuring and overheard me. Exasperated, she took the electric kettle besides the air pot, filled it with a little water and switch it on. The water boiled in about 1 minute.

Air pot and kettle I was embarrassed. I was caught not thinking. Not looking for the solution when it was right in front of my eyes. My mind wanted to excuse myself because it was wee hours in the morning but i knew it wasn’t the case. 

It was a habit of allowing my mind to become lazy, to gripe and grumble whenever i encountered difficulties. Difficulties are just events to help us think and grow. 

A Smooth Sea never made a skilled sailor ~ Franklin D. Roosevelt

It was a wake-up call for me. Time to set some goals and start thinking!

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Physical Movement – The Last Strategy to Learn Chemistry

Mr Khemistry

Strategy #11: Physical Movement

This post is the last strategy of the series on Dr Lee’s book, ‘Internal Drive Theory’. If you have not read the previous strategies, click here to start.

Basically, by interspersing mundane repetitive tasks with physical movements, it helps break the monotony. Doing so will also allow children with short attention span to focus on a long task. By breaking it up into manageable chunks, the child/student is able to stay awake and alert over long periods. This is especially helpful for teachers trying to keep students awake after lunch/recess. 

Challenges using Physical Movement

  1. Knowing when to use it. Task that requires prolonged concentration such as writing an English composition shouldn’t be interrupted.
  2. How much physical movement to incorporate. Some physical movements takes too long and wastes too much time. The child might end up more interested in the physical movement than on the task. Observe the situation and vary the number/length of interrupts accordingly.

How to use Physical Movement

  • Make sure the task is repetitive and does not build on each other, doesn’t break their train of thought.
  • If the child/student is able to focus, there is no need to introduce physical movement.
  • Be creative in the type of physical movement you choose.
  • Limit the time for the interruption.

These interruptions will ensure that time passes quickly and the child/student completes the work without falling asleep or losing focus. At the end of the task, use it to sculpt their Self-Concept (Strategy #8) using affirmative words. 

For JC students, they are old enough to come up with their own study process. Teach them to observe themselves, how long can they stay focus on studying. For example, if they need two hours to finish a 6-7 question chemistry tutorial, they might need to break it up into two sessions. Depending on what physical activities they enjoy, they can choose to grab an ice-cream or login for a quick game on their mobile app. 

That’s it for the last strategy. Underpinning all eleven strategies is Strategy #2, so make sure your child/student trusts you. 

As Uncle Ben says famously to Spiderman, “With great power comes great responsibility.”

You now know of strategies to motivate your child/student to study/behave in the way you believe is the best. It’s up to you to not use it for your own pride but rather for their well-being. Anything done excessively is always bad, guide them to lead a balanced life. Both work and play should be balanced (though it might not always be 50/50).

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Strategy #10: Specify and Magnify

Mr Khemistry

Specify and Magnify

This is strategy #10 from Dr Lee’s book, ‘Internal Drive Theory’. If you have not read the previous strategies, click here to start!

This method looks for the positive behaviors and points it out. Amplifying it. This increases the child/student’s motivation level. 

The challenges for this method:

  1. Lack of patience. It requires patience to actually look for the good in the child/student.
  2. Tendency to judge the wrong instead of waiting and appreciating the right.
  3. What to magnify. For academic studies, we can focus on the wrong things. Which might at best waste their time. At worst, it may cause them to lose marks.
  4. When this method is taken to the extreme. E.g. you appreciate them doing their work, then all they do is work and forsake play.

At JC level, it’s not so easy to pick out good in the student when you only spend about two hours with them every week. Humans have a tendency to notice what’s wrong instead of what’s right, teachers included. Sometimes teachers can misinterpret or over-compensate for comments made in the A level Chemistry markers’ report. For example, students putting the wrong dipole moment for hydrogen bonding diagram. Teachers end up getting them to put dipole moment for every atom to prevent them from putting it on the wrong pair of atoms. 

How to make use of this method:

  • Find out what is good. For example, what are the marking points
  • Be observant to pick out positive behaviors
  • Be patient. Wait for the opportune time
  • Make sure the emotional connection is strong
  • Provide a positive model, i.e. you model the behavior
  • Ignore the negative. For the moment.

That’s it for strategy #10. Go to the last strategy!

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Set Goals to Learn Chemistry

Mr Khemistry

Came across this really good TedEx talk by Stephen Duneier on goal setting, watch it if you have the time.

Well, we’re reach the 3rd last strategy by Dr Lee in her book “Internal Drive Theory”. If you haven’t read the previous strategies, start here.

Strategy #9 – Set Goals to Learn Chemistry

Dr Lee starts by stating why it’s important to set goals. It helps the child/student visualise what they want to achieve. Due to the focus of time and energy on a specific goal. And when they’ve achieved the goal, they feel elated. 

One of my favorite speaker, Jim Rohn, used to say, ‘There are two kinds of people when it comes to facing the future. One with fear and apprehension and the other, with anticipation. The difference lies in the fact that those who anticipate, designed their future.’

Goal-setting then, is a simple exercise in ‘designing’ your future. There’s short term goals and long term goals. The point about setting goals is you have to be specific. There’s no point in setting a vague goal, you wouldn’t even know if you’ve achieved it!

Challenges of goal setting

Calibrating Goal Difficulty – this point has been brought up before but it’s good to remind ourselves that the goal has to be doable with some effort. If it’s totally out of their league, the child will be demoralized and give up without trying. 

Before setting the goal, have a sense of how motivated the child is. If he/she is low on motivation, give easy goals and frequently praise them upon completion of each task. If they are motivated, set goals which will stretch them. Only set those “impossible” goals when you have good rapport and available to give timely feedback. Doing these goals will help to build up his self-efficacy. Remember that if your child/student fails, both fails.

Second challenge is to set some grand blanket goal and use threats. You may achieve those goals, but at the emotional expense of the child/student. I remember as a student, i have respect for teachers who are firm but fair. I’m afraid of the discipline master because he is usually very fierce. I would do assignments from both but one is out of respect, the latter is out of fear.

At JC level, it’s amazing to note that many students still do not set goals. They are mostly drifting along, whatever score they can get, that’s it. I remember when i was in Secondary school, i had a close friend who would always compare grades after every test. I wasn’t a competitive person, so at the end of the day, i did not keep up. My wife tells me that she too had a friend like that, but the difference is, my wife was the top student in class. Sometimes having a goal (a person to beat), can motivate us to work harder. How can we foster more friendly competition at JC level Chemistry?

That’s it for strategy #9. Go to strategy #10!

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