O-Level Chemistry: The pH Scale

The pH Scale

The pH Scale is a set of numbers from 0 to 14 which is used to indicate whether an aqueous solution is acidic, neutral or alkaline.

All aqueous solutions contain hydrogen ions, H+ and hydroxide ion, OH-. The concentration of these ions differs in solutions of different pH values. Therefore, the pH of a solution is related to the concentration of hydrogen ions or hydroxide ions present in a solution.

It is important to appreciate the formal definition of “pH” in order to master Chemistry. It is formally defined as the “measure of the concentration of the hydrogen ions in a solution”.

Based on the definition above, let’s look at three different sections of the pH Scale:

A) Solution with pH equal to 7


This if the pH of pure water i.e. distilled water.

The concentration of hydrogen ions and hydroxide ions is the same.

B) Solution with pH less than 7


Acids have concentration of hydrogen ions more than the concentration of hydroxide ions.

The lower the pH value, the greater the concentration of hydrogen ions and the lower the concentration of hydroxide ions, which means the more acidic the solution.

C) Solution with pH greater than 7


Acids have concentration of hydroxide ions more than the concentration of hydrogen ions.

The higher the pH value, the greater the concentration of hydroxide ions and the lower the concentration of hydrogen ions, which means the more alkaline the solution.

Let’s take a look at a Chemistry MCQ question.

Question 1:

An unknown aqueous solution has a pH value of about 2.

Which of the following is correct about the ions present in the solution?

A) Concentration of H+ ions = High  & Concentration of OH- ions = None

B) Concentration of H+ ions = High &  Concentration of OH- ions = Low

C) Concentration of H+ ions = Low &  Concentration of OH- ions = High

D) Concentration of H+ ions = Low & Concentration of OH- ions = None

Work on it and write your answer in the comment section below. See you soon!

PS: Feel free to share this blog post to anyone who might benefit from it.

Most Effective Way of Learning

“Monsters exist, but they are too few in number to be truly dangerous. More dangerous are the common men, the functionaries ready to believe and to act without asking questions” ~ Primo Levi

O and A Levels Chemistry & Maths - Keep Asking

The best way to learn in life (not just in schools) is to ASK QUESTIONS. Not just attend lectures & classes and copy down every single English words by the lecturers/teachers. Students need to listen attentively and ask questions when in doubt.

At Winners, we practice this method of educating our students and always encourage them to “Clarify Whenever in Doubt”, that “Every Question is a Good Question” & “there’s Always Something Useful to Learn”.

We also encourage our students to start asking questions in their schools for every subjects cos this is the only effective way of learning.

Personally, we have seen so many students who improved from a F9/E8/D7 grades to A1/A2/B3 grades for Chemistry & Maths in very very short period of between 2-6 months. It is POSSIBLE for students to truly Unleash Their Potential, if they start to ASK.

For both O-Levels (as well as IGCSE) and A-Levels (including IB & IP), we provide platforms for our students such as 1) email support 2) SMS support, in order for them to clarify their doubts ASAP. Frankly, it’s really hardwork on our side but we believe it’s worth it cos it will build their confidence & momentum in clarifying doubts.

In the picture, it’s our current Sec 4 student clarifying her doubt for a Chemistry concept/question via WhatsApp messaging. She has improved so much in Sec 3 last year and we are sure she will do well for O-Level this year, if she continue to stay consistent and clarify her doubts asap. Whoosh!

I believe many of our graduate students (some in university while others already started their working career) will appreciate this very important learning tool in life.

If you happen to read this post, do remember: KEEP ASKING!

PS: Feel free to share this post with any students (including adults) who is really serious about learning effectively.

Enjoy the learning journey everyone!
Sean Chua

2014 GCE O-Level Chemistry 5073 – Paper 2 Post Mortem

[For Singapore Students taking 2014 GCE O-Level Pure Chemistry Exam; Subject Code: 5073]

Chemistry Paper 2 Post

How do i put it? Besides getting our students to study very hard on ALL topics, i must say that we were pretty lucky this year. In the last 2 weeks of revision, we went through a couple of concepts which came out almost exact in Paper 2 (Written) on Tuesday 28th Oct 2014 and are worth lots of marks, namely:

  • Titration Curves which appear in 4 pages of Paper 2
  • Multiple-Step reactions involving Dibasic Acid e.g. H3po4 + NaOH

In terms of topics, let’s take a look at what have been heavily tested in Paper 2 (Written Paper) according to our own students as well as comments that we gather from facebook/twitter/blogs:

  1. Experimental Chemistry (not tested in Paper 2)
  2. Methods of Purification & Separation (not tested in Paper 2)
  3. Identification of Ions and Gases a.k.a. Qualitative Analysis (not tested in Paper 2)
  4. Kinetic Particle Theory (not tested in Paper 2)
  5. Atomic Structure (not tested in Paper 2)
  6. Chemical Bonding and Structure of Matter (about 3 – 4 marks in Paper 2)
  7. Formulae, Stoichiometry and the Mole Concept (about 4 marks in Paper 2)
  8. Electrolysis (one whole question in Paper 2)
  9. Energy from Chemicals (a few marks in Paper 2)
  10. Speed of Reaction (about 2 marks in Paper 2)
  11. Redox (about 2 marks in Paper 2)
  12. Acids and Bases (about 2 marks in Paper 2)
  13. Preparation of Salts (not tested in Paper 2)
  14. Ammonia (about 2 marks in Paper 2)
  15. The Periodic Table and Group Trends (one whole Data Bank Question in Paper 2)
  16. Metals and Reactivity Series (about 2 marks in Paper 2)
  17. Air and the Atmosphere (not tested in Paper 2)
  18. Organic Chemistry: Fuels, Alkanes, Alkenes, Alcohols and Carboxylic Acids (lots of marks in many questions in Paper 2)
  19. Organic Chemistry: Macromolecules (few marks being tested in Paper 2)

Based on what have been tested in Paper 2 (Written), we are looking forward to the following concepts to be tested in Paper 1 (MCQ) on 11th Nov 2014:

  • Experimental Chemistry
  • Methods of Purification & Separation
  • Identification of Ions and Gases a.k.a. Qualitative Analysis (lots of marks?)
  • Kinetic Particle Theory
  • Atomic Structure
  • Preparation of Salts (lots of marks?)
  • Speed of Reaction
  • The Periodic Table and Group Trends (lots of marks?)
  • Metals and Reactivity Series (lots of marks?)
  • Air and the Atmosphere (lots of marks?)

Now, let us be even more strategic.

Paper 1 consists of 40 multiple-choice questions (total of 40 marks) and the weightage is a WHOPPING 30%, in case you are not aware of it. Doing well in Paper 1 will definitely bump up your overall Chemistry grade. In view that Paper 1 is only for 1 hour, you must not waste time. In fact you have an average of 1.5 minutes for each question.

If you are a student taking your GCE O-Level Pure Chemistry (syllabus code: 5073) and would like a final dash to score 40/40 marks, i welcome you to join us in our annual Score 100% MCQ Workshop on 8 Nov 2014.

All the best for the final Chemistry paper. See you at the finishing line.

PS: Feel free to share this blog post with your friends who will benefit from it! Keep sharing & learning! :)