SimpleChemConcepts Tips

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:

O-Level Pure Chemistry & Combine Science (Chemistry): Nov/Dec 2011 Headstart & Revision Workshops Registration

sean — Fri, 04 Nov 2011 08:39:14 +0000

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: