Question

Calculate the pOH corresponding to each of the pH values listed, and indicate whether each solution is acidic, basic, or neutral. a. \(\mathrm{pH}=1.02\) b. \(\mathrm{pH}=13.4\) c. \(\mathrm{pH}=9.03\) d. \(\mathrm{pH}=7.20\)

Short answer

a. pOH = \(12.98\), Acidic solution b. pOH = \(0.6\), Basic solution c. pOH = \(4.97\), Basic solution d. pOH = \(6.80\), Weak basic solution

Step-by-step solution

Determine pOH values

To find the pOH values, we will use the formula: \(\mathrm{pH} + \mathrm{pOH} = 14\). So, we have: a. pOH = \(14 - \mathrm{pH} = 14 - 1.02 = 12.98\) b. pOH = \(14 - \mathrm{pH} = 14 - 13.4 = 0.6\) c. pOH = \(14 - \mathrm{pH} = 14 - 9.03 = 4.97\) d. pOH = \(14 - \mathrm{pH} = 14 - 7.20 = 6.80\)

Identify the nature of each solution

Now, we will use the pH values to determine if the solutions are acidic, basic, or neutral. a. The pH value is \(1.02\), which is less than \(7.0\). So, the solution is acidic. b. The pH value is \(13.4\), which is greater than \(7.0\). So, the solution is basic. c. The pH value is \(9.03\), which is greater than \(7.0\). So, the solution is basic. d. The pH value is \(7.20\), which is slightly more than \(7.0\). So, the solution is a weak basic solution. Here is a summary of our results: a. pOH = \(12.98\), Acidic solution b. pOH = \(0.6\), Basic solution c. pOH = \(4.97\), Basic solution d. pOH = \(6.80\), Weak basic solution

Key concepts

pH and pOH relationship

In acid-base chemistry, understanding the pH and pOH relationship is crucial. They are both measures of hydrogen ion concentration in a solution, with pH reflecting the acidity and pOH the alkalinity. These two scales are interconnected by the formula: \[ \mathrm{pH} + \mathrm{pOH} = 14 \] This equation shows that pH and pOH are inversely proportional, meaning if one goes up, the other comes down. This relationship helps to identify if a solution is acidic, basic, or neutral, simply by knowing one of these values. If we know the pH value, we can easily calculate the pOH value by subtracting the pH value from 14. This is an essential concept in performing chemical calculations related to acid-base balance.

Acidic and Basic Solutions

Acidic and basic solutions are differentiated based on their pH values. A solution is considered acidic if its pH is less than 7. This occurs when there are more hydrogen ions than hydroxide ions in the solution.

• Acidic Solution: pH < 7
• Example: Vinegar with pH around 2.4

Conversely, a basic or alkaline solution has a pH greater than 7, indicating a higher concentration of hydroxide ions compared to hydrogen ions.

• Basic Solution: pH > 7
• Example: Baking soda in water with pH around 9

Knowing whether a solution is acidic or basic is crucial for various applications, including chemical reactions, biological processes, and industrial applications.

Neutral Solutions

A neutral solution carries a balanced pH value of exactly 7, meaning the number of hydrogen ions equals the number of hydroxide ions. The most classic example is pure water. In a neutral solution, both pH and pOH are 7 because: \[ \mathrm{pH} + \mathrm{pOH} = 14 \] So, \( \mathrm{pOH} = 14 - 7 = 7 \). Neutral solutions are significant because they serve as a baseline or reference point in many chemical calculations and reactions. Without any excess of hydrogen or hydroxide ions, neutral solutions do not affect the acidity or basicity of substances they are mixed with.

Chemical Calculations

Performing chemical calculations is an important skill in acid-base chemistry. These calculations involve determining the pH, pOH, the acidic or basic nature of solutions, and much more. To illustrate, if you know the pH of a solution, using the relationship \[ \mathrm{pH} + \mathrm{pOH} = 14 \] simplifies finding the pOH. Once you have these values, you can easily identify the solution's nature:

• pH < 7: Acidic
• pH > 7: Basic
• pH = 7: Neutral

Chemical calculations allow scientists and students to predict how different substances will react together and how they will affect their environment. Hence, mastering these calculations is essential for anyone involved in chemistry.