SimpleChemConcepts Tips

How can Sean help my child in his O-Level Chemistry?

sean — Fri, 25 May 2012 06:07:04 +0000

For the past few days, I saw many students with their parents walking out of schools with their report books. It’s the Meet-the-Parents sessions after the mid-year exams.

How did your child perform?

In any case, give him the credit for putting the effort regardless of how little or how much the amount. We must acknowledge studying is a stressful process in Singapore.

Given the amount of time students spend in their CCAs and outside school activities, many don’t have much time and even energy left for their self-study.This is certainly not an excuse for them to under perform.

And come this June holidays, they should have more time for their self-study but many students might have no idea how to start or simply lack the motivation to start their revision.

I’m here to help!

For the 5th year running, I’m conducting the O-Level June Intensive Revision Workshops to build students’ confidence and understanding on a topic by topic basis.

Being focused is the key to effective revision this June and we have proven it year after year to have worked out well for our students.

Visit our website to find out how your child can benefit from our Intensive Revision Workshops this June Holidays!

Call us at 9828 7357 to speak to us too!

I look forward to helping your child to realize his potential this June Holidays!

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O-Level Chemistry: Redox Reactions (Reduction & Oxidation) – Hydrogen Atoms

sean — Wed, 29 Feb 2012 22:51:14 +0000

In the previous post, you have learnt that OXIDATION is the gain of oxygen atoms and REDUCTION is the loss of oxygen atoms.

Today, we shall discuss them based on the gain or loss of hydrogen atoms.

OXIDATION is also the loss of hydrogen atoms and REDUCTION is also the gain of hydrogen atoms.

E.g. Reaction of hydrogen sulfide and chlorine to form hydrogen chloride and sulfur

H₂S(g) + Cl₂(g) –> 2HCl(g) + S(s)

In the above chemical reaction, hydrogen sulfide has lost hydrogen, hence it has been OXIDISED.

Chlorine, on the other hand, has gained hydrogen and is therefore REDUCED.

Hydrogen sulfide is considered the REDUCING AGENT as it has caused the the reduction of chlorine.

Chlorine, on the other hand, has caused the oxidation of hydrogen sulfide and is therefore considered to be the OXIDISING AGENT.

In the above chemical reaction, we say it is a REDOX Reaction since both OXIDATION and REDUCTION occurs simultaneously.

Note:

An OXIDISING AGENT helps the other substance to get OXIDISED, and itself gets REDUCED.

A REDUCING AGENT helps the other substance to get REDUCED, and itself gets OXIDISED.

Hope you find the above discussion on REDOX Reactions (based on Hydrogen atoms) useful. Feel free to share it with your friends that are taking O-Level Chemistry (or IGCSE, IB and IP Chemistry).

Hmm…before i end this post, how about trying out a question that test you on the above fundamentals?

Quick Check 1:

Copper (II) oxide reacts with hydrogen based on the following equation:

CuO(s) + H₂(g) –> Cu(g) + H₂O(l)

State the substance that

(i) has been oxidised

(ii) has been reduced

(iii) is the oxidizing agent

(iii) is the reducing agent

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O-Level Chemistry: Redox Reactions (Reduction & Oxidation) – Oxygen Atoms

sean — Mon, 27 Feb 2012 15:35:49 +0000

REDOX reactions are reactions that involves both Reduction & Oxidation simultaneously.

There are 4 ways to look at whether a substance has been oxidised or reduced, and they are:

1. Gain/Loss of Oxygen atoms

2. Gain/ Loss of Hydrogen atoms

3. Gain/Loss of Electrons

4. Increase/Decrease in Oxidation States/Numbers

Today we will discuss Oxidation / Reduction based on oxygen atoms.

When a substance gains oxygen in a chemical reaction, we say it has been oxidised. The reaction is called OXIDATION.

When a substance loses oxygen in a chemical reaction, we say it has been reduced. The reaction is called REDUCTION.

E.g. Magnesium reacts with copper (II) oxide to produce magnesium oxide and copper metal.

Mg(s) + CuO(s) –> MgO(s) + Cu(s)

From the above equation, you can see that copper (II) oxide has lost oxygen, so it has been REDUCED.

Magnesium, on the other hand, has gained oxygen and so has been OXIDISED.

Now, the copper (II) oxide is said to be an OXIDISING AGENT because it has given oxygen to magnesium and caused the oxidation of magnesium.

The magnesium, on the other hand, is said to be a REDUCING AGENT because it has taken oxygen from copper (II) oxide and caused the reduction of copper (II) oxide.

In the above chemical reaction, we say it is a REDOX Reaction since both OXIDATION and REDUCTION occurs simultaneously.

Note:

An OXIDISING AGENT helps the other substance to get OXIDISED, and itself gets REDUCED.

A REDUCING AGENT helps the other substance to get REDUCED, and itself gets OXIDISED.

Hope you find the above discussion on REDOX Reactions (based on Oxygen atoms) useful. Feel free to share it with your friends that are taking O-Level Chemistry (or IGCSE, IB and IP Chemistry).Related Articles:

O-Level Chemistry: Question on Chemical Bonding

sean — Mon, 16 Jan 2012 16:40:15 +0000

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:

Release of GCE O Level 2011 results on 9 Jan 2012

sean — Thu, 05 Jan 2012 14:50:09 +0000

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: