O-Level Chemistry: Strength versus Concentration of Acids


In the previous blog post, we have watched a video on the difference between Strength of Acids and Basicity of Acids.

If you have missed it, you can click HERE to watch it.

Today, we are going to discuss another misconception by many students studying basic Chemistry.

It is very important not to confuse the Strength of Acids with the Concentration of Acids.

I have observed that many of my GCE O-Level and IGCSE Sec 3 and Sec 4 Pure Chemistry Tuition Class students are confused by what they have learned from their school’s Chemistry teachers or previous home-based Chemistry tutors. It usually take me some effort to re-align their concepts and associated keywords.

As we have learned in the previous blog post, Strength of Acids refers to the extent of dissociation (or ionisation) of an acid. We will see words like “STRONG” and “WEAK“.

Concentration of Acids is different. It refers to how much of an acid (the solute) is dissolved in the solution. We will see words like “CONCENTRATED” and “DILUTE“.

Note that the strength of an acid is not affected by its concentration.

A dilute acid solution is not the same as a weak acid solution, and a concentrated acid solution is not the same as a strong acid solution.

i.e Dilute Acid  Weak Acid

i.e Concentrated Acid  Strong Acid

A strong acid will dissociate completely regardless of its concentration (whether it’s dilute or concentrated).

A weak acid will dissociate partially regardless of its concentration (whether it’s dilute or concentrated).

The term concentration is actually a concept covered in the topic of Mole Concepts or Mole Calculations.

The concentration of a solution is given by the amount of a solute dissolved in a unit volume of the solution.

Recall that a solution is made up of a solute and a solvent i.e. Solution  Solute + Solvent

As such, concentration of an acid can be easily changed!

You can decrease the concentration of an acid solution by adding more solvent to it.

You can also increase the concentration of an acid solution by adding more solute to it.

However, the strength of an acid cannot be changed!

A strong acid like HC(aq) will always dissociate completely to produce a high concentration of hydrogen, H+ ions, regardless of whether the solution is dilute or concentrated.

A weak acid like CH3COOH(aq) will always dissociate partially to produce a low concentration of hydrogen, H+ ions, regardless of whether the solution is dilute or concentrated.

Hope the above explanation is clear to you.

Together with the previous blog post, i have discussed on the difference between these three common terminologies used in the topic of Acids and Bases, namely:

Strength of Acids  Basicity of Acids  Concentration of Acids

I hope you find the content easy for your understanding and if you have any questions, leave me a comment below.

Feel free to share this blog post with your friends who needs help in mastering Chemistry.

PS: You can do a search on the top right hand corner for more discussions and questions on “Acids and Bases” or select from the suggested blog posts under “Related Articles” below.

PPS: If you are based in Singapore and want to master Acids, Bases and Preparation Salts, i will be conducting an annual Topical Chemistry Revision Workshops during the June School Holidays. You can get in touch with us at PassWithDistinction.com to find out more.

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Many people talked about teaching Chemistry, I simply LOVE it. I am a passionate Chemistry Coach based in Singapore, Southeast-Asia and aspire to be one of the most dynamic, powerful and humorous speakers in Asia. My 18+ years of coaching experience has equipped me to understand the true reasons why students are not able to perform well in Chemistry, and allow me to structure my teaching methodology to cater to different levels of learners. If you have found this post useful, please share it with your friends. I would really appreciate it! Sean Chua

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