SPM Chemistry Form 4 Notes – Acids and Bases (Part 5)

by BerryBerryTeacher

in Berry Reference (Notes)

The pH scale is just a scale using colours to represent the concentration of hydrogen ions. In SPM Chemistry (and real-life applications), it has more far reaching consequences as it is a measure of acidity and basicity of an aqueous solution. It is typically used as a quick indicator to see if an aqueous solution is acidic or basic by judging the value from the pH scale. A pH above 7 is said to be basic while below 7 is touted to be acidic. Then obviously, 7 is taken to be neutral.

This post, Part 5 of Berry Berry Easy study notes on Acids and Bases for SPM Form 4 Chemistry students is all about the fascinating and important pH scale. So try your best to understand it, you’ll need it in your future life and also for examination purposes.

[Tips: Most students think of the pH scale as being linear. While the values are linear, the value it measures, the Hydrogen ion concentrations are measured in logarithmic scale. So if the value of an aqueous solution is 1 higher than that of another, it has not 1 time more hydrogen ion concentration but 10 times more. So take note of that. Also, the hydrogen concentration measured here is relative to water rather than any absolute figures, in case you are asking how do you have 1/10,000,000 Hydrogen ions.]

SPM Chemistry Form 4 Notes – Acids and Bases (Part 5)

pH-scale(The above image is just a representation, colours may vary, so please follow the colours described in the table below)

The pH scale and the Measurement of pH Value of a Solution

 

  • pH scale is a set of numbers used to represent the degree of acidity or alkalinity of a solution.
  • pH is a measurement of the concentration of hydrogen ions (H+) in the solution.
  • pH value greater than 7: alkaline solution
  • pH value of exactly 7: neutral solution
  • pH value less than 7: acidic solution
  • In an acidic solution = higher in the concentration of the H+ ions, the lower the pH value.
  • In an alkaline solution = lower in the concentration of the H+ ions, the higher the pH value.
  • pH solution can be measured by using universal indicator, pH paper and pH meter.
pH value Colour of Universal Indicator
0, 1, 2 Red
3 Orange red
4 Orange
5 Orange yellow
6 Yellow
7 Green
8 Greenish-blue
9 Blue
10 Blue
11 Bluish-purple
12, 13, 14 Purple

You have reached the end of this post. In the next part, Part 6 of Berry Berry Easy study notes on Acids and Bases for SPM Form 4 Chemistry students, Berry Readers will learn about the strength of acids and alkalis. So do check back soon.

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