Dear GCE ‘O’ Level (as well as IP) students using Marshall Cavendish Chemistry Textbook as reference text,

Please note that there is a printing error in the chemistry textbook (third impression 2008) that many of you did not realised (just like many of my students, until recently).

The error in print is on (more…)

Hi Students (based in Singapore),

With GCE ‘O’ Levels and IGCSE Chemistry Examinations in 2 months time,how many of you are prepared to score the grades you desire for Chemistry?

Many of you seemed to realise that this is time for you to really sit down and revise what you have learned for the last 2 – 3 years. This can be shown by the number of emails i received from students as well as the numerous comments on the Chemistry questions posted recently in this Chemistry Blogsite.

I am glad you are taking actions! =)

Based on the numerous requests from parents & students, we have decided to re-run 2 of our Chemistry Topical Mastery Workshops this September school holidays, in order to assist you.

If you have missed the workshops during the June Holidays, this is the chance for you to learn it from us again.

And for those that realised that you can’t answer questions related to these topics, I would strongly urge you to join us whatever it takes, due to 3 reasons:

1. High Weightage in Exams EVERY YEAR!
2. Highly Application Topics – No way you can memorise and expect to do well
3. Sure it will come out! No way to escape from it!

Details of the 2 Mastery Workshops as follows:

Mole Calculations Mastery Workshop 2009

(3rd time we are running this year due to overwhelming response)

>> Click HERE for Early Bird Price Registration by 31st Aug 09

Redox & Electrolysis Mastery Workshop 2009

(Back by popular demand and enquiry)

>> Click HERE for Early Bird Price Registration by 31st Aug 09

There is a saying that “80% of the Success is just about Taking the Necessary Actions”.
This is your last chance to help yourself towards Success!

Register early and enjoy early bird savings + bonuses!

If you need any assistance, please call 9685 7675 or 9828 7357

I look forward to seeing you at the workshops!

PS: Seats are limited! Registration will close once seats are filled!

PPS: A-Math Differentiation & Integration Mastery Workshop also available. Click HERE for more info

To Your Academic Success in Chemistry,
Sean Chua
Master Trainer for Chemistry
Winners Education Group (more…)

Hello everyone,

My sincere apology for missing in the month of June. =)

I was busy with coaching several groups of committed O Levels / IGCSSE / IB / IP students that wanted to improve their Chemistry Concepts (and thus their academic grades) in an intensive manner during the June School Holidays in Singapore. Phew! It’s finally over!

Topics that were discussed included the followings:

1. Atomic Structure & Chemical Bondings – Basic but Most Important Essential Concepts
2. Acids & Bases – relate to our everyday life actvities i.e. shampoo, coffee, rainwater, etc
3. Salts & Qualitative Analysis – Super Memory Techniques & Flow-Charts for effective learning and ease of memorisation
4. Periodic Table Trends & Metals – discussion on O Level Examination Application Questions
5. Rate of Reactions & Energy Changes – Applications questions in O Levels Chem Exam. No way you can score well just by memorising definitions
6. Redox & Electrolysis – a “4-Step System” taught to ensure students will always get the answer correctly with confidence
7. Mole Calculations – “See-Saw Method” plus other Systems taught to ensure students answer questions confidently & correctly

The above topics will cover about 70 – 80% of the syllabus for GCE ‘O’ Level Examinations.

This Intensive Revision Programme (in which ALL essential concepts were discussed for each topic) was physically tiring but mentally & emotionally fullfilling. The feeling was estatic each time when we finished one workshop (2 topics), when i see students having more interest in the topics and scoring better in the Post-Tests (as compared to their Pre-Tests). I am confident to say that the students leave the workshops with more confidence and desire to score the grades they truly deserved.

You can view the video below on selected photos that were taken:

You can check out the URL HERE.

If you have missed our June Intensive Revision Programme, you can be posted of our upcoming workshops by filling up your details HERE. In addition, we will also be conducting our annual ‘O’ Levels Organic Chemistry Mastery Workshop 2009 in late July. More information will be furnished within the week.

In the next 2 weeks, i will be blogging more on the misconceptions and common mistakes that i observed during this June Intensive Programme.  Stay Tuned! =) (more…)

I would like to say a big thank you for all of my local and international readers (Students,Parents, Educators) for following my Chemistry blog all these while. It is my joy to receive questions and compliments from my readers, suggesting I have helped them using my expertise in Chemistry some way or another.

This June Holiday 2009, I would like to invite all Singapore students (Secondary 3 and 4) to join me in our annual June Intensive Revision Programme. I would be personally coaching you on the following topics:

1. Atomic Structure & Bonding (Ionic, Covalent & Metallic)
2. Acids, Bases
3. Salts & Qualitative/Chemical Analysis
4. Periodic Table and Metals
5. Rate of Reactions & Energy Changes
6. Redox & Electrolysis
7. Mole Concepts & Chemical Calculations

For more registration details, click here

It will include

• Comprehensive 100% coverage of each topics
• Understand abstract concepts in an (more…)

In the previous blogpost, we have discussed on the 2nd criterion for predicting products of electrolysis for aqueous solutions under the Series on “Secrets of Redox and Electrolysis“.

Today we will end the series by introducing the 3rd criterion:

Consider: Nature of Electrodes Used in Electrolysis

Different products are discharged at the electrode when different type of electrodes are used.
When we say different types of electrodes used, it simply means:

Inert Electrode (such as Carbon and Platinum) vs Reactive Electrode (such as Cu or Silver)

We shall once again look at it in a step-by-step simplified approach.

Lets consider 2 electrolysis reactions using Copper(II) Sulphate as the electrolyte.

Set-Up A: Inert Electrodes such as Platinum

At the +ve Anode:

• 4OH-(aq) –> 2H2O(l) + O2(g) + 4e-
• SO42- ions remain in solution

At the –ve Cathode:

• Cu2+(aq) + 2e- –> Cu(l)
• H+ ions remain in solution

Summary:

• Overall reaction is: 2CuSO4(aq) + 2H2O(l) –> 2Cu(s) + O2(g) + 2H2SO4(aq)
• Acidic solution of H2SO4(aq) formed at end of reaction

Set-Up B: Reactive Electrodes such as Copper

At the +ve Anode:

• Cu(s) –> Cu2+(aq) + 2e-
• Anode dissolves to form Cu2+ ions in aqueous solution

At the –ve Cathode:

• Cu2+(aq) + 2e- –> Cu(l)
• H+ ions remain in solution
• Cathode becomes coated with a layer of reddish-brown Cu

Summary:

• Cu is transferred from the anode to the cathode
• Cu cathode slowly increases in mass
• Cu anode decreases in mass
• Colour & Concentration of CuSO4 remain unchanged
• No effective loss of Cu2+ ions from the CuSO4 solution

Let’s check out 1 question to see how much you understand.

Question:
Aqueous copper(II) sulphate is electrolyzed using copper electrodes. Which observations will be made?
Anode (+ve) Cathode (-ve) the electrolyte
A. anode dissolves           pink solid forms          blue colour fades
B. anode dissolves           pink solid forms           no change
C. colourless gas forms   colourless gas forms    no change
D. colourless gas forms   pink solid forms blue   colour fades

PS: Remember to leave down your answers in the “Leave A Reply” section below.

PPS: To learn everthing on Redox & Electrolysis, please visit the section right below called “Table of contents for Secrets of Redox & Electrolysis“

In the previous post, we have discussed on the 1st criterion for predicting the products of electrolysis for Aqueous Solutions, that is to determine the Position of Metals In The Reactivity Series.

Today, we are going to look at the 2nd criterion, that is:

Effect of Concentration of Solution on Effective Discharge

• It applies only to ANIONS
• Only for Concentrated Solutions
• An increase in the concentration of an anion tends to promote its discharge

Example:

Consider Electrolysis of concentrated NaCl solution using carbon electrodes.
2 types of anions are attracted to the anode: Cl- and OH- ions

According to the reactivity series, OH- ions should be discharged preferentially (as we have seen in the previous post on diluted aqueous solutions). However, Cl- ions are far more numerous than OH- ions and so are discharged instead.

Try out this question to see if you understand this concept.

Question:

What would you observe when a concentrated solution of HCl is electrolyzed using Platinum electrode? Explain your observations and write down the equations involved.

PS: Remember to leave down your comments and suggested answers in the “Leave Your Reply” section below.

We have discussed on the strategies to predict the products of electrolysis of molten compounds as electrolytes in the earlier post.

Today, we are going to examine the Strategies to Predict the Products of Electrolysis for Aqueous Solutions.

For aqueous solutions, there is more than 1 type of cations and anions, since water is present.
Water will contribute to H+ and OH- ions in addition to the ionic compound that is present.

When more than one type of cations or anions are present in a solution, only 1 cation & 1 anion is preferentially selected for discharge.

The selectivity discharge of ions depends on 3 factors:
1. Position of metal in the reactivity series
2. Concentration of the ion in the electrolyte
3. Nature of the electrode used

Let’s check out on the 1st Criterion to consider – Position of Metal in Reactivity Series

Ease of Discharge of Cations Increases down the list:

Potassium Ion, K+
Sodium Ion, Na+
Calcium Ion, Ca2+
Magnesium Ion, Mg2+
Aluminium Ion, Al3+
Zinc Ion, Zn2+
Iron Ion, Fe2+
Lead Ion, Pb2+
Hydrogen Ion, H+
Copper Ion, Cu2+
Silver Ion, Ag+

Ease of Discharge of Anions Increases down the list:

Sulphate Ion, SO42- (Do not discharge)
Nitrate Ion, NO3- (Do not discharge)
Chloride Ion, Cl-
Bromide Ion, Br-
Iodide Ion, I-
Hydroxide Ion, OH-

As such, Cu2+ is preferentially discharged @ the -ve cathode, if we have Cu2+, H+ and Fe2+ in aqueous solutions.

And for anions in aqueous solutions, we will have OH- ions preferentially discharged over NO3- and Cl- if we have all of them in the solutions.

So far so good? Let’s check one of question:

Question 1:

If we have a soluton of dilute aqueous NaCl solution and inert platinum electrode is being used,

(i) What ions are present in the electrolyte?

(ii) What are the products @ the cathode and the anode?

PS: Leave us your suggested answers directly below this post at “Leave Your Reply” section.

I hope you have been learning something so far. =))

Up next, we will visit the 2nd Criterion for predicting the products of electrolysis:
“Concentration of Aqueous Solutions”

PPS: I am launching a book called “Up Your Chemistry Grades Now!” in ebook version before i send it to publisher for the hardcopy book to be available in majoy bookstores.  As it takes sometime for the hardcopy book to be published, i want to ensure graduating students sitting for major examination soon, will have a chance to get hold of this wonderful book that i have compiled over 10 years of Chemistry Coaching. It includes all the Common Errors and Misconceptions that many students made batch after batch, and the Correct Essential concepts you need to know .  Also included are the Definitions that you need to know in O Level Chemistry Exams and also Tips on what the Examiners are Looking For. If you studying very hard for your Chemistry but yet to score the marks that you truly deserve, make sure you are the first to have your hand on it. You can sign-up for more information on the launch of this wonderful book here.