O-Level Chemistry Made Easy

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

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. : )