Learning pH Scale in IB Chemistry

Learning pH Scale in IB Chemistry the Simple Way
The pH scale is an important concept in IB Chemistry and understanding it can be difficult. This guide explains the basics of hydrogen ion concentration, why the pH scale is important, and how to use it to evaluate various solutions.

What is the pH Scale?
The pH scale is a measure of the hydrogen ion concentration (H+) in a given solution. It ranges from 0 to 14 and reflects the amount of acidity or alkalinity present. Generally, solutions with a pH lower than 7 are said to be acidic and those with a pH greater than 7 are considered to be basic or alkaline. Solutions with a pH of 7 are considered neutral.

How to Determine the Acidity of Solutions
To determine the acidity of solutions, you can plot the concentration of hydrogen ions (H+) on a graph. This graph is called a pH scale. Solutions with an H+ concentration between 0-7 will be considered acidic in nature, while solutions with an H+ concentration above 7 will be considered basic or alkaline. Solutions with a neutral pH are those that have the same number of hydronium ions (H3O+) as hydroxide ions (OH-).

Hydrogen Ion Concentration and pH Calculation
To calculate the pH of a solution, you need to measure the hydrogen ion concentration in moles per liter (mol/L). A lower reading indicates the sample is more acidic, while a higher reading indicates it is less acidic. If a sample’s H+ concentration is 10-7 mol/l or lower, then it will have a pH value of 7 or lower and be considered an acid.

Examples of Calculating Acidic and Basic Solutions on the pH Scale
As a general rule, anything below pH 7 is acidic, while anything above it is basic. Let’s look at two examples of how to calculate solutions on the pH scale. For example, if you have a solution with a hydrogen ion concentration of 10-5 mol/l, then its pH value would be 5. Similarly, if the H+ concentration was 10-9 mol/l, then it would have a pH of 9.

Relationship Between Hydrogen Ion Concentration and pH
The pH of a solution is directly proportional to the hydrogen ion concentration, which means that as the hydrogen ion concentration of a solution increases, so does its pH. For example, if you have two solutions with different concentrations of hydrogen ions, then the one with the higher concentration will have a higher pH value than the other. This linear relationship between H+ and pH can be used to accurately measure and predict the acidity or alkalinity of a solution.

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