Category : A level syllabus

Alkene Concept Map

Mr Khemistry

Alkenes Functional Group Concept Map

Alkenes concept map

You can use this series of organic concept maps to familiarize yourself with the various transformations of the functional groups.

Using this format, we can also practice drawing skeletal structures for organic molecules.

You can download this and print it out for your own usage, not for distribution please 🙂

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Kinetics – The Big Idea by Mr Khemistry

Mr Khemistry

Kinetics

Kinetics is the study of speed/rate of a chemical reaction.

Definition: Rate of reaction is the change in concentration of reactant or products over time.

Question: How do we know what’s the change in concentration of reactant or products?

Ans: We have to MONITOR it.

Question: How do we monitor it?

Ans: Look at the reaction equation, what has changed from left-hand side (LHS) to the right-hand side (RHS)? We can monitor colour intensity (colourimeter), volume of gas evolved (downward displacement of water/gas syringe), loss of mass (mass balance), change in pressure (manometer), electrical conductivity, pH (pH probe, titration) etc.

Image result for colorimeter

Colorimeter

Main Product

Manometer

An important term in this chapter is “Order of Reaction”. We can only determine the order of reaction with respect to a particular reactant through experiments. Note: Order cannot be determined from the chemical equation.

Consider this chemical reaction:

A + B -> C + D

To find the order wrt reactant A, we will have to conduct expts keeping B constant and varying [A] to monitor the effect on rate. Likewise, to find the order wrt B, we will need to keep A constant and vary [B]. One of the ways to keep the other [reactant] constant is to make it in large excess.

To find out more about kinetics or other topics, come join our weekly JC tuition classes at bukit timah shopping centre.

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Chemical Equilibrium Summary Table

Mr Khemistry

Chemical Equilibrium Summary Table

The qualitative aspect of Chemical Equilibrium can be summarized into the table below.

From the table, we can see that changes in concentration, pressure and catalyst does not affect Kc/Kp. The only factor that does affect equilibrium constants is temperature. Also, we would need to know whether the forward reaction is endo or exothermic to predict the effect temperature change will have on it.

Note that increasing temperature increases both the rate of forward and backward reactions. However, the rate of the endothermic reaction will be increased more than the rate of the exothermic reaction.

If the enthalpy change for the reaction is zero, temperature will have no effect on the equilibrium. Similarly, if the reaction has the same number of moles of gaseous particles on both sides, pressure will have no effect on it.

An interesting point to note is catalysts have no effect on position of equilibrium and equilibrium constant. The only effect it has is to increase the rate of both forward and backward reactions to the same extent.

If this article has helped you understand chemical equilibrium better, hit the social sharing button below and share it with your friends!

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Relationship between Kc and Kp – Chemical Equilibrium

Mr Khemistry

Relationship between Kc and Kp – Chemical Equilibrium

I was updating the chemical equilibrium notes this week and thought it would be good to share this with all of you.

Didn’t know how Kc and Kp was related and i was stumped by a question about 10 years ago when i was still teaching in a JC.

Relationship between Kc and Kp

The main idea is to use the ideal gas equation to substitute partial pressures in concentration terms.

Once you got it, it’s quite easy to remember 🙂

Hope you’ve found this useful, if it was, do share it with your friends via the social media buttons below.

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FRS Chemical Environment

Mr Khemistry

FRS Chemical Environment

FRS Chemical Environment

U and V are structural isomers with molecular formula C7H16.

Both U and V produce the same number of possible structural isomers upon reaction with chlorine to form monochlorinated compounds with the formula C7H15Cl.

Which pairs are possible structures of U and V?

Or

Have a look at the different colour coded hydrogen atoms. Those with the same colour is the same type of hydrogen, i.e. they will form the same product if they are substituted by chlorine. 

Do look out for plane of symmetry as it will greatly accelerate the speed at which you identify FRS Chemical environment.

So answer is 1 and 3 only!

If you’ve enjoyed this organic MCQ, do share it with your friends and see if they are able to do it quickly.

Join us for our weekly tuition classes where we will tackle more of such questions together!

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Book published!

Mr Khemistry

H2 Chemistry Practical Guide book

 

This is one item on my bucket list i thought wouldn’t be fulfilled so soon. Hopefully this book will be of help to private candidates as they prepare for their practical paper.

Current students might also like to get a copy to get more practices of the various topics.

Please share if you know of anyone who might benefit from this book, thanks in advance!

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Advice for private A level candidates

Mr Khemistry

Private Candidates

Hi there, are you a private candidate looking to re-take the A levels?  If so, have you thought about the reason why you didn’t do well last year or the year before?

Whenever i see a private candidate re-taking the A levels, i would ask them if they’re aware that the odds are stacked against them doing better than when they were in college.

Firstly, you are no longer in an environment of learning. For the guys, most of them are serving NS, girls are working part-time. It’s an understatement to say you are NOT among
people in the same life-stage as you are. Meaning peer discussions and sharing studying tips are out.

Secondly, the structured learning that a school environment offers is no longer there. Instead, what you have are probably people who couldn’t care less whether you studied or not.
Without the discipline to complete assignments, the weekly practise of doing lab work and waking up early to study, the odds are that you will be lulled into inactivity most of the time.

Thirdly, resources are very thin for A level subjects outside of school. I’ve had a look at popular’s selection of A level assessment books and i do think sometimes that even Carousel might
have more useful resources. You need LOTS of practise.

What can you do?

Tuition is an option but it is probably not enough. What is crucial is that you get a complete set of materials, including revision packages, from your ex-JC. And then work out a schedule together with some friends to set a timetable for revising the syllabus. It is advisable if your finances permit, to hire an experience tutor to guide/mark your work together with a few other private candidates. If you are taking sciences, please consider registering at a private school such as BMC to practise doing lab work.

Be resourceful and change the way you approach the exam. Re-doing what you did the last time will probably yield the same or worse results.

Good Luck!

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Branches of Chemistry at Advanced Level

Mr Khemistry

Branches of Chemistry

Physical, inorganic and organic Chemistry

3 branches of Chemistry

In Physical Chemistry, we mostly encounter formulas and calculations. There is theory but the main applications involves calculations and numerical answers. The most important thing we need to do is to practise. This is similar to Mathematics where you basically have to use the formulas to do calculations for different questions until we are proficient in it. Most students make the mistake of just reading the worked examples in their lecture notes and tutorials. Remember, if you don’t have time to practise it, you wouldn’t do well for it.

In Organic Chemistry, the most basic level is to actually memorise all the reagents and conditions for the different functional groups. A student counted and said it was well over 80. Well, just remembering these reagents and conditions is just the first step. You would need to know how does the different functional groups interchange between each other. A very helpful method is to draw up mindmaps for each of the functional group and combine them to form a massive diagram where you can draw links between each group. It is likely that A level exams requires you to apply existing knowledge of organic mechanisms to solve questions in novel context.

Lastly, for Inorganic Chemistry, you will need to understand how periodicity works, i.e. trends. The way the periodic table is arranged is in patterns. Group I elements all have one valence electron, period 2 elements all have 2 quantum shells etc. After understanding how the trends are formed, you are expected to make predictions based on these trends and state cases of anomalies.

In a nutshell, this is how i see the 3 branches of Chemistry studied at A levels 🙂

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Changes to H2 Chemistry Syllabus Part 2

Mr Khemistry

H2 Chemistry Syllabus 2017

Part 2 (part 1 here)

H2 chemistry syllabus 2017 updates:

Organic: Constitutional (structural) isomerism. Cis-trans isomerism, used to be geometric isomerism. Enantiomerism used to be optical isomerism.

Nitrogen Compounds (proteins): Not required to learn primary – quaternary structures, as well as list major functions of proteins in the body. Not required to recognize the twenty amino acids and describe α-helix and β-pleated sheet. Not required to describe protein components of haemoglobin. Not required to explain denaturation of proteins.

Electrochemistry: state and apply the relationship Δ = −nFEθ to electrochemical cells. spontaneous redox reaction (ΔG < 0) would mean that Ecell > 0. In other words, the extent of a redox reaction is governed by the sign and magnitude of cell, like in the case of Δ.

Since Eθcell is dependent on both temperature and concentration (Nernst equation), a non-spontaneous reaction under standard conditions can be made feasible under non-standard conditions (e.g. increasing temperature or concentration).

Similar to the use of ΔGθ to predict the feasibility of a reaction, Eθcell only gives an indication of the thermodynamic feasibility (spontaneity), i.e. based on energy consideration.

The other important aspect, the kinetic feasibility (looking at the activation energy, Ea) must also be considered in order to understand fully whether a reaction is likely to proceed on its own. 

Note that “standard conditions” for both Electrochemistry and Energetics is now 298K, 1 bar and 1 moldm-3 

Atomic structure: Describe the shapes of d orbitals. This ties in well with the explanation for splitting of degenerate (same energy level) d orbitals.

Transition elements: Describe, using the shape and orientation of the d orbitals, the splitting of degenerate d orbitals into two energy levels in octahedral complexes.

In an octahedral complex, a central metal atom is surrounded by 6 lone pairs of electrons (on the 6 ligands). dx2_y2 orbital and the dz2 orbitals have their lobes pointing at the ligands along the x and y axes, and z axis respectively, hence they experienced greater repulsion from the ligands. The dxy, dyz and dxz orbitals experienced less repulsion since their lobes do not point at the ligands along the axes. Thus the 5 d orbitals are split into 2 energy levels, with higher energy level dx2_y2 and dz2 orbitals and the dxy, dyz and dxz orbitals having the lower energy level

End of H2 Chemistry Syllabus 2017 update~

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