Determine each of the following for a 0.100 M HBr solution:
a. [H₃O⁺]

Verified step by step guidance

1. Step 1: Recognize that HBr is a strong acid, meaning it completely dissociates in water. The dissociation reaction can be written as: $HBr\; \to \; H⁺\; +\; Br⁻$. Since it dissociates completely, the concentration of $[H⁺]$ (or equivalently $[H₃O⁺]$) will be equal to the initial concentration of HBr.
2. Step 2: Identify the given concentration of HBr, which is 0.100 M. This means that for every mole of HBr, 1 mole of $H⁺$ ions is produced.
3. Step 3: Use the relationship between the concentration of HBr and $[H₃O⁺]$. Since HBr dissociates completely, $[H₃O⁺]\; =\; [HBr]$. Therefore, $[H₃O⁺]$ is equal to 0.100 M.
4. Step 4: Write the final expression for $[H₃O⁺]$ as $[H₃O⁺]\; =\; 0.100\; \backslash text\{\; M\}$. This is the hydronium ion concentration in the solution.
5. Step 5: Verify the logic by recalling that strong acids like HBr fully dissociate, so the concentration of $[H₃O⁺]$ directly matches the initial molarity of the acid.

Key Concepts

Strong Acids and Ionization

Strong acids, like HBr, completely dissociate in water, meaning that all the acid molecules break apart into ions. For a 0.100 M HBr solution, this results in a concentration of H⁺ ions equal to the concentration of the acid, which is 0.100 M. This complete ionization is crucial for calculating the hydronium ion concentration.

Hydronium Ion Concentration

The concentration of hydronium ions, [H₃O⁺], in a solution is a measure of the acidity of that solution. In the case of strong acids, the concentration of H₃O⁺ is directly derived from the concentration of the acid. For a 0.100 M HBr solution, the [H₃O⁺] is also 0.100 M, reflecting the complete dissociation of the acid.

pH Scale

The pH scale quantifies the acidity or basicity of a solution, with lower values indicating higher acidity. It is calculated using the formula pH = -log[H₃O⁺]. For a 0.100 M HBr solution, knowing the [H₃O⁺] allows us to calculate the pH, which is an essential aspect of understanding the solution's properties.