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Organic Chemistry MCQ Analysis

Mr Khemistry

Organic Chemistry MCQ

Organic Chemistry MCQ: Which of the following compounds exhibit cis–trans isomerism?

    1. organic molecule
    2. organic molecule 2
    3. organic molecule 3

Analysis: The question is straightforward. Which compounds exhibit cis-trans isomerism? In the Chemistry H2 syllabus, we learnt about the two criteria for cis-trans isomerism.

  • Presence of C=C bond
  • Different atoms/group of atoms bonded to each of the carbon atoms

Although in the H2 Chemistry syllabus, it is required that C=C bond cannot be in a cyclic structure.

Looking at the three options, looks like none of them can exhibit cis-trans isomerism! But this cannot be the case, let us examine the options carefully.

The three options examined

Option 1: Although there’s no C=C, there is a four-carbon ring structure which restricts rotation. Moreover, the two central carbon atoms each have different atoms bonded to it. So it is able to display cis-trans forms!

Option 2: This is outright wrong as it violates the rule that C=C bond cannot be in a cyclic structure. (But we shall see that the cyclic structure is only limited to 7 carbon ring and below)

Option 3: This is not in the H2 syllabus as cis-trans isomerism can be exhibited by C=C bond in a cyclic structure having more than 7 carbon atoms. Click here to find out more

This Organic Chemistry MCQ isn’t the run-of-the-mill type. Two of the options involves knowledge outside of the H2 syllabus. Most likely, this question is meant to challenge the stronger ability students to read beyond their syllabus requirements. Also, it expose students to a novel context that is slightly outside of their comfort zone.

In our weekly classes, we let students have a chance to try out these challenging questions to stretch them. If you liked doing this question, come join us and broaden your horizon!

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Solving Organic Deductive Questions

Mr Khemistry

Solving Organic Deductive Questions

Compound J, C8H6O4, forms a molecule K, C8H10O3, when reacted with LiAlH4 in dry ether. However, when J was reacted with NaBH4 instead, a product of molecular formula C8H8O4 was formed.

J gives an orange precipitate with 2,4-dinitrophenylhydrazine but does not give any precipitate when warmed with Fehling’s reagent. K reacts with bromine water to form L, C8H7O3Br3.

Suggest the structures of J, K and L. 

Solution:

First information is the molecular formula, it has almost the same C to H ratio and has more than six carbons => likely to have benzene ring C6H6

(Note that there is still two carbon atoms not accounted for)

When it undergoes reduction with LiAlH4, 4 hydrogen atoms were added but 1 oxygen atom was removed. => likely to have one COOH group, accounts for 2 oxygen atoms

But when it undergoes reduction with NaBH4, only 2 hydrogen atoms were added. 
=> confirmed one of the reduction by LiAlH4 was on COOH

J undergoes condensation with 2,4-DNPH but does not undergo oxidation with Fehling’s reagent. => carbonyl but not aliphatic aldehyde. Possible to be aromatic aldehyde or ketone.

K  undergoes electrophilic substitution (tri-substitution) with bromine water => phenol present and also 2,4,6 positions does not have any substituent groups. This means that the two remaining carbon atoms must be at 3 and 5 positions. Additionally, this means that ketone is no longer possible as we would need two carbon on the same substituent group.

Summary: From the above deductions, J has phenol, aromatic aldehyde and carboxylic acid on positions 1,3,5.

K has phenol and two primary alcohols.

L has tri-substituted Br on positions 2,4,6, phenol, aromatic aldehyde and carboxylic acid on position 1,3,5.

deductive question

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Distinguishing Organic Compounds

Mr Khemistry

Distinguishing Organic Compounds

Distinguishing alkenes

 

 

 

 

Suggest one simple chemical test to distinguish them from each other. State the reagents and conditions needed and give the expected observations for each compound.

 

Analysis:

This pair of compounds are both dienes, meaning they both contain two C=C bonds. 

We will not be able to distinguish them by using chemical tests for alkenes. This is true for any pair of compounds with the same functional group(s). For example, esters, secondary alcohols, amides etc.

The tip is to distinguish them base on their structures. Use structure-specific tests such as iodofoam test and KMnO4.

For the pair of compounds above, note that the double bonds are closer for cyclohexa-1,3-diene. Using hot acidified KMnO4 will yield carboxylic acid for both compounds but one of the product for cyclohexa-1,3-diene is is ethandioic acid which will further oxidize to carbon dioxide and water.

Answer:

Add KMnO4(aq), H2SO4(aq) and heat to both compounds.

Observation: Both solutions will change from purple to colourless but the solution of cyclohexa-1,3-diene will produce effervescence of CO2 that form white ppt with limewater

Extra practise:

distinguishing esters

 

 

Distinguishing organic compounds is one of the easier types of questions in H2 Chemistry, be sure to score here!

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How to solve Organic Synthesis Question

Mr Khemistry

Organic Synthesis Question

Organic synthesis question

In any synthesis questions, we first need to note the number of carbon atoms, is there an increase or decrease in the carbon chain?

In the above question, yes the carbon chain increased from 8 to 9 carbons. This informs us that somewhere in the intermediate steps, a step-up reaction involving nitrile group will be needed. 

Then we take a look at the changes in the functional groups. We are starting with alkene and ending with alkene and carboxylic acid group.

To insert a nitrile group, we need to first add halogenoalkane functional group as a precursor. This is a common way to introduce the CN group via nucleophilic substitution in the H2 Chemistry Syllabus.

Next we need to consider how to keep the C=C group in the target molecule. Inevitably, when we add the halogen to the C=C, the alkene functional group will disappear. So how do we reform the C=C after adding the halogen? 

There are 3 options,

  1. HCl
  2. Cl-Cl in tetrachloromethane
  3. Cl-Cl in aq

First option is out as it will convert the functional group to halogenoalkane, which leaves us no way to reform the alkene through elimination.

Second option is also out as both Cl will be substituted by CN group.

Option 3 is our answer as Cl will be added to the the terminal carbon atom and OH will be added to the more substituted carbon atom (Markovnikov Rule) Choosing the correct reagents and condition for the first step is crucial to solving the question as it will set the course of synthesis.

Sequencing the Synthesis Route

After which we can just substitute the terminal Cl with CN and hydrolyse it to COOH. The alkene group can also be reformed via elimination of water.

Organic Synthesis Question

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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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Design the Self-Concept to Learn Chemistry

Mr Khemistry

This is Strategy #8 of Dr Lee’s book, ‘Internal Drive Theory’. If you have not read the previous seven strategies, click here.

Words are powerful. They send a subliminal message from the physical world to our subconscious. Our subconscious mind has no way of telling which words to believe and which words to keep out. That is a job only the conscious mind can do. So as parents and educators, we need to be VERY careful what are the words that come out of our mouths. 

I used to think that if i could just not label students as being “stupid”, i am doing pretty well. But now i know, even body language, sighs and words have the ability to demotivate a student and discourage them from even trying. There are many research showing how when we put labels on a child/student, they will behave in such a way to live up to that label. For example, if you mix in average students with the brightest students in class 5A, over time, those average students will come to see themselves as being bright. And they behave accordingly. 

Challenges of designing the Self-Concept

Parental fears – Sometimes we project our fears onto what the child randomly does. We pass judgement and hence sculpt the unformed self-concept of the child/student. When we repeat it often enough, it becomes a self-fulfiling prophecy. 

Learning how to ride a bicycle, we are told not to focus on the tree, but on the road. But guess what happens? We focus on the tree and steer the bicycle into the tree. This is a all too common scenario. We become that which we fear. Or in this case, we mold our children/students into what we fear.

How can we consciously design their Self-Concept?

By passing GOOD judgement using a positive example of behavior. And if they do naughty acts from time to time, separate the act from the child’s self-concept. It’s difficult but necessary. One analogy that is familiar to some of us is how God separates the sins from the sinner. He hates the sin (act) but loves the sinner (the person).

Sometimes, certain experiences will cause the child/student to come to the conclusion that they are not smart or capable. We need to tell them it is not true. Rather, it is due to a lack of effort. Then show them by working with them through the challenges and celebrating mini-victories. By showing them that they can change their results through effort, they will learn to see that poor results is not final and is can be improved upon.

For JC Chemistry, they need to understand the concept. And explaining it with scientific terms. One of the challenges i face as a JC tutor is some of their self-concept is already ingrained. For example, “I am not good in calculation questions. I cannot remember the reagents and conditions.” These are simply not true. Anyone can practise more to get better in calculations. And using concept maps, most students are able to remember a big chunk of reagents and conditions over time. Getting better is simple, but it’s not easy. 

That’s it for strategy #8, go on to strategy #9!

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