Chemical Bonding is one of the most important fundamental topics in O-Level Chemistry (and other equivalent Basic Chemistry syllabus). It is linked to many other topics in Chemistry. However, many students are not aware of it and take them very lightly.

Let’s check out a question that was emailed to me by one of the student that read this blog.

Hi

I just want to clarify whether the explanation is correct.

Q) Explain why graphite has a lower melting point than diamond. (1 mark).

The answer is “Graphite has fewer covalent bonds than Diamond.”

What about this answer:

“Graphite has weak van der wals forces between the layers. Lesser energy is required to overcome such forces. As a result, it has a lower melting point than diamond”.

Is this answer acceptable?

From my own understanding, diamond has 4 covalent bonds between the carbon atoms while graphite has 3 covalent bonds between the carbon atoms and weak van der wals forces. More energy is required to break the extra covalent bond in diamond than the weak van der wals forces between the layers of atoms in graphite.

Regards
Weijie

The suggested answer “Graphite has fewer covalent bonds than Diamond.” is INCORRECT and is one of the common mistakes made by students batch after batch every year. Not sure where he found this suggested answer though.

Weijie is correct in his own suggested answer. =)

Graphite  are made up of layers of hexagonal rings that are held together by weak intermolecular  van der Waals’ forces of attraction. Lesser energy is required to overcome such weak forces. As a result, it has a lower melting point than diamond which is made of carbon atoms that are covalently bonded strongly together to form an extensive 3-D network with tetrahedral arrrangement. A large amount of energy is required to break these strong covalent bonds.

Tips:

Covalent Bonds (an intramolecular bond) is much stronger than van der Waals’ forces (an intermolecular bond)

Remember to master this topic on Chemical Bonding if you want to excel in Chemistry. : )Related Articles:

• Chemistry Phenomenon: Diamond, A Giant Macromolecule
• More Error in Marshall Cavendish GCE ‘O’ Level “Chemistry Matters” Textbook – Part 2
• O Level Chemistry: Energy Changes (Exo/Endo) & Bond Energy
• O Level Chemistry Question: Chemical Bonding & Structural Properties
• O Level Chemistry: Which has lower Melting Point

It’s official!

Release of GCE O Level 2011 results is on 9 Jan 2012, Monday from 2pm onwards.

More details on www.seab.gov.sg.

It’s the time of the year where hard work and focus for the past 2 years reaps its rewards.

I hope you are one of those that put in your hardwork to make it happen.

Students who have been preparing for this day will be excited with the possibility of the freedom of choices in their path of further education.

All the best and enjoy the process!

PS: for those that will be taking your GCE O Level examination this year, now is the time to start clarifying your doubts. Don’t hesitate! Get your concepts right ASAP. Related Articles:

• Options Galore – Choosing the Right Path for O-Level holders
• 2007 GCE O Level Examination Results – release in 24 hrs
• Tips for O Level Chemistry Paper 1 (MCQs) Exam
• Options Available – After getting your GCE O Level results
• Start Preparation Early = Confidence

To Register, Click the link http://www.winnerseducation.com/nov-dec-workshops/

Time flies, we are nearing the end of academic year 2011 as the O-Level & A-Level students take their respective exams this month. It has been my pleasure coaching them in the last 10 months or more.

Let’s fast-forward to Academic Year 2012, there will be another batch of students taking their Secondary 3 End-of-Year Exams or GCE O-Level Exams. If you are one of them, i just want to advise you to start learning the proper CONCEPTS early, especially when it comes to CHEMISTRY. This is because the fundamentals are really important and it will help you to connect all the topics together.

This coming November and December school holidays, i will be again be personally coaching a selected group of committed students to improve their Chemistry Concepts. If you would like to be one of them to enjoy learning Chemistry, i welcome you to join us in the following workshops:

A) Basic Essential Concepts (Headstart) Workshop:

Date: 17 & 18 Nov 2011 ( 9am – 1pm)

This is primarily for Sec 3 (2012) students that has little or no knowledge in Chemistry Concepts. I will be coaching you on the fundamentals that will get you to be very comfortable when your school chemistry teacher discuss them in class. This will give you a headstart and not feeling confused like many of your peers. Chemistry is very new when you progress from Sec 2 to Sec 3 and many students tend to lose their interest in Chemistry after a few months in school.

It is also suitable for Sec 4 or 5 (2012) students that score less than 55% in the end-of-year exam. Frankly, you need to build up all these fundamentals, like writing Chemical Formula 100% of the time, writing Balanced Chemical Equation 100% of the time. Do not procrastinate anymore. Trust me.

B) Acids, Bases & Preparation of Salts (Revision) Workshop:

Date: 5, 6 & 7 Dec 2011 (9am – 1pm)

This is a revision workshop and is suitable for Sec 4 or 5 (2012) students.

Acids, Bases & Preparation of Salts are three very important topics that all Chemistry students must be familiar and confident with. They are highly related to the Sec 4 or 5 application topics and thus will determine whether you prepare well for your major exams or not in 2012.

However, i realised many students hate these three topics! Most complained that there are lots of things to memorise. They said that their teacher ask them to memorise the whole sections in the book in order to do well. Hmm…Please note – this is a misconception! Memorising might not get you to even pass. Instead of memorising, i would instead ask you to understand the Essential Concepts, so that you can attempt any questions that are posed to you in exams. Isn’t that better?

To Register, Click the link http://www.winnerseducation.com/nov-dec-workshops/

Limited Seats only.

Seat you at the workshops!

PS: Workshops suitable for IB, IGCSE and IP students also, depending on your level and what you have learned in your respective school. Do check with your child or call us to discuss on suitability.

PPS: For those that would also like to register a seat for our 2012 Weekly Classes, you can do so by clicking the following link: http://www.winnerseducation.com/register-o-level/Related Articles:

• Updates: December 2010 Chemistry Revision/Headstart Workshops
• O Level Chemistry Revision Workshop – Completely Sold Out!
• Master Organic Chemistry and Score 15 to 25 More Marks!
• 2010 Chemistry: Sec 3 Headstart & Sec 4 Revision (Dec Holiday Programmes) – Early Bird Registration
• Introductory Workshop to O Level Chemistry Intensive BootCamp

Note: For Singapore GCE O-Level Pure Chemistry Combine Science (Chemistry) students that are taking exams this coming week

Following are some quick questions that my O-Level Chemistry students asked me last two days as they revise their work and need to clarify some doubts before their exams.

I thought it would be great to share with all my readers (especially if you are one of those going for the exam also). Questions are posted in BLACK while my suggested answers / comments are posted in BLUE.

If you find the post useful to your friends, feel free to share the link with them. =)

Questions from Elizabeth:

Hi Mr Chua, I have 21 questions for you, could you kindly respond accordingly? Thanks ((:

1) What is the precision of measuring cylinder & pipette?

Measuring cylinder is to 1 cm³ accuracy.

Pipette normally is not used for measurement. Instead it is used to transfer specific volume of liquid/solution.
E.g 10 cm³, 25 cm³, 50 cm³, etc.

2) What exactly is calcium chloride?

It is an ionic compound / salt.

3) Is metal sulphate a salt?

Yes. Metal sulfate is a general term. So many examples you can easily think of are: Sodium sulfate, calcium sulfate, magnesium sulfate, etc.
They are all ionic compound / salt.

4) During O’s, for the test for sulphate, do I write:
-add nitric acid, then barium nitrate
OR
-add acidified barium nitrate?

Both can. And you will see either form in the questions in O-Levels. Adding nitric acid means to acidify barium nitrate solution.

5) To test for chlorine, do I use damp litmus paper OR damp blue litmus paper?

Given a choice, we would prefer to write damp blue litmus paper.
It turns from blue to red and then bleached.

6) What exactly happens when liquid freezes?

Liquid state changes to solid state.

Refer to Kinetic Particle Theory topic to understand how the ARRANGEMENT and MOVEMENT changes from L to S state.

7) What is the definition of ‘volatile’?

It refers to liquid that easily changes to gaseous state at room temperature.
E.g. Ethanol in perfume.

Sometimes, they apply it to solids that sublimes also. E.g. Solid iodine sublimes to become gaseous iodine at room temperature.

9) Does concentration affect cations?

Don’t understand this question.

10) For O’s,are these the only soluble hydroxides we need to know- Zinc, Aluminium & Potassium?

We talked about this before. I disagree with your answer above.
We usually remember Group I metal hydroxides are soluble in water (NaOH, KOH, LiOH)
as well as Ba(OH)₂ for Group II metal hydroxides. Ca(OH)₂ is sparingly soluble.

Zinc hydroxide and Alumnium hydroxide are INSOLUBLE! Refer to QA, test for Cations.

11) What does energy level on the energy profile diagram represent?

It shows 3 things.

1. Reactants higher or lower energy than Products
2. Enthalpy change is negative or positive
3. Presence of Activation Energy

12) In exo reactions, why do products have lower energy?

In EXO, enthalpy change is NEGATIVE.

Refer to the formula of:  Enthalpy Changes = H_B-B + H_B-M

Use the formula and reason out the thought process.

H_B-B is endo (+ve) whereas H_B-M is exo (-ve).

You will get it. Refer to textbook if you still dont. They give very good examples to understand.

13) Which is the definition of catalyst?

- Provide an alternative route for the reaction with lower activation energy?
- substance which speeds up the rate of reaction

Yes. Combine both sentence into one answer.

14) For the oxidation of ethanol, for the chemical equation, do I write 2[O] or O₂?

If due to bacterial oxidation, we should write O₂.

If used acidified potassium dichromate (VI) in lab, we normally write as 2[O].

Check textbook to re-affirm.

15) Is Group 1 hydroxides soluble?

Answer above.

16) For Group 1(Apart from SPA) salts, do I use titration or Excess method?

Theoretically, use TITRATION.

17) What are found ‘free’ in the ground?

The more common elements are Gold, Platinum and maybe silver.

18) For reduction by carbon, when do you know it will give Carbon Monoxide/ Carbon Dioxide?

I mentioned this before.

The equation required in your O-Level Pure Chemistry (code: 5072) is showing the use of carbon monoxide as the reducing agent.

Thus, the products from the reduction of iron (III) oxide in Blast Furnace should be MOLTEN IRON and CARBON DIOXIDE.

Forget about the carbon monoxide that your teacher told you it will happen for the prelim papers.

It is not in syllabus.

If O-Level it comes out, they will give you alot of clues if they want you to write the product as MOLTEN IRON and CARBON MONOXIDE.

19) Can Silver and Gold be reduced by Carbon and Hydrogen?

You meant Silver oxide? They can, but it is not necessary. You can simply heat it to get Silver metal.

Gold usually are found uncombined in the earth.

20) Do I write ‘Calcium Sillicate’ OR ‘slag’ for my answer during O level?

It is Calcium Silicate. You have made a spelling error.

Both should be fine if they asked for substance.

But if they ask for chemical name, then you should write Calcium Silicate.

If they asked for Chemical Formula, then you write it as CaSiO₃.

21) When I add bromine to an AlkAne, do I say it decolourise slowly OR there is no observation?

I supposed you meant adding aqueous bromine, Br₂(aq).

Alkanes are saturated hydrocarbons and will not react with aqueous bromine. Thus, no changes. Aqueous bromine remains reddish-brown.

Only alkenes will decolourised the reddish-brown aqueous bromine since they are unsaturated.

Thanks in advance for answering (:

Sent from my iPhone

Questions from Lay Teng:

Her questions are in fact from the Pass With Distinction book that i wrote for Shinglee Publisher.

1) When questions ask about compare & contrast, do we have to mention both Similarity & Differences?

Yes. You need to. Let’s say questions ask us to compare and contrast Evaporation & Boiling process, you are required to mention the similarity and differences.

Similarity: Both involves the change of state from liquid to gas of water.

Differences:

A. Boiling is fast while evaporation is slow

B. Boiling is throughout the whole liquid while evaporation only at the surface

C. Boiling occurs at 100 ^oC (BP of water) while evaporation occurs below the boiling point

2) How come the book state Caesium atom and Caesium ion has different number of shells? And why the atom and ion has the same mass?

The answers given in the book is correct.

Caesium atom has 6 electron shells. When it gives away one electron, it forms Caesium ion which has only 5 electron shells.

Mass number is only determined by the sub-atomic particles present in the nucleus. i.e. protons + neutrons.

Since when atom becomes ion, only electrons are transferred, the mass will stay the same.Related Articles:

• Chemistry Phenomenon – Sublimation Process
• O Level Chemistry – Physical & Chemical Properties of Alkalis
• O Levels Chemistry 2008 Exam Question: Organic Chemistry in Paper 1 (MCQs)
• O Level Chemistry: Assigning State Symbols in Chemical Equations (Exercise)
• O Level Chemistry SPA: Color of Copper Hydroxide Vs Copper Carbonate Vs Soluble Copper Salts

Note: This blog post is more for students taking the GCE O-Level Pure Chemistry Examination in Singapore

Every year during this period, i will share with students (and their parents) how they can boost their Chemistry grade even if they didn’t do well in your Paper 2 (Structured Questions). It’s by focusing their attention and energy on Multiple Choice Questions (MCQ) Paper 1.

It requires sheer determination!

I know exactly how you will feel with most papers completed and just the MCQ Papers towards the end of O-Level. I’m here to help: I’m here to keep you from being complacent, I’m here to help you to prepare confidently for your final dash!

Score 100% in Chemistry MCQ will definitely boost your results! Its weighting is 30%!

Also, the early bird registration for Score 100% MCQ Mastery Workshop is closing this Sunday, 16 October 2011.

Click here to register.

If you’re committed to scoring your A for Pure Chemistry, I invite you to join us.

Date: 12 November 2011
Time: 9 am – 5 pm
Venue: Kaplan City Campus @ Wilkie Edge, Selegie Road.
Suitable for: GCE O-Level Pure Chemistry Candidates 2011

We are left with 10 seats 8 seats only. Register now!

Click here to register.

“It is good that Sean has organized this workshop to focus on the MCQ of Chemistry paper as it is often a paper that teachers and students alike will neglect. Through the workshop, he covers tricky and common MCQ questions, which is very helpful. His cheerful and lively teaching approach learns to keep everyone awake and in focus. Thanks Sean for everything! Definitely recommended to other students in future.”

- Edna Chan Zhi Yin, Hougang Sec School

May the force be with you,
Sean Chua
Master Trainer (Chemistry) & AuthorRelated Articles:

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• Introductory Workshop to O Level Chemistry Intensive BootCamp
• Be like the tortoise – Final Dash for ‘O’ Level Chemistry
• Free Introductory Workshop (Last One!) to O Level Chemistry Intensive BootCamp 2008
• Announcement: O Levels Organic Chemistry Mastery Workshop – Early Bird Registration Starts!