Problem 37 - Chemistry The Molecular Science

Question

The measured \(\mathrm{pH}\) of a sample of seawater is 8.30 . (a) Calculate the \(\mathrm{H}_{3} \mathrm{O}^{+}\) concentration. (b) Is the sample acidic or basic?

Step-by-Step Solution

Answer

(a) \([H_3O^+] = 5.01 \times 10^{-9} \, M\). (b) The sample is basic.

Step 1: Understanding pH and \\([H_3O^+]\\) Relationship

The pH of a solution is related to the hydronium ion concentration, \([H_3O^+]\), by the formula \([H_3O^+] = 10^{-\text{pH}}\). This formula allows us to calculate the concentration of hydronium ions in a solution if the pH is known.

Step 2: Calculate \\([H_3O^+]\\) Using the pH Value

Given \(\text{pH} = 8.30\), we can find \([H_3O^+]\) using the formula: \[ [H_3O^+] = 10^{-8.30} \]Using a calculator, \([H_3O^+] = 5.01 \times 10^{-9} \, M\).

Step 3: Determine If the Sample is Acidic or Basic

A solution is considered acidic if its pH is less than 7, neutral if its pH equals 7, and basic if its pH is greater than 7. Since the pH of the sample is 8.30, it is basic.

Key Concepts

Hydronium Ion Concentration

The concept of hydronium ion concentration is crucial in understanding the acidity of solutions. When we talk about hydronium ions, we're referring to \( [H_3O^+] \), which tells us how many hydronium ions are present in a solution.
The concentration of these ions is directly related to the pH of the solution.The mathematical relationship between pH and hydronium ion concentration is given by:

• \( [H_3O^+] = 10^{-\text{pH}} \)

This equation allows you to calculate the concentration of hydronium ions if you know the pH of a substance.
In our example with a pH of 8.30, the calculation becomes:

• \( [H_3O^+] = 10^{-8.30} \)
• Using a calculator, \( [H_3O^+] \approx 5.01 \times 10^{-9} \, M \)

This small concentration suggests fewer hydronium ions, showing the solution is not very acidic.

Acidic or Basic Solution

To determine if a solution is acidic or basic, you can rely on the pH level. This is a scale that ranges from 0 to 14 and helps in categorizing substances quickly and easily. Here's a simple way to remember:

• A solution is acidic if its pH is less than 7.
• A solution is neutral if its pH is exactly 7.
• A solution is basic if its pH is greater than 7.

In our example, since the pH is 8.30, it is clearly above 7.
This means the seawater sample is basic. Understanding whether a solution is acidic or basic is essential in fields ranging from biology to environmental science as it impacts chemical reactions and biological processes.

pH Scale Interpretation

Interpreting the pH scale is easier once you get the basics down. The scale runs from 0 to 14. Each step on the scale represents a tenfold change in hydronium ion concentration. Key points about the pH scale:

• A pH of 7 is neutral, like pure water.
• Values below 7 indicate an acidic solution—think lemon juice or vinegar.
• Values above 7 signify a basic (alkaline) solution—like baking soda or seawater.

So, when you encounter a pH value like our 8.30, it fits into the basic range.
Knowing how to read the pH scale helps you predict how substances will behave in conjunction and understand their potential biological or chemical effects.