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.

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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