pH & Hydrogen Ions (AQA A-Level Chemistry): Revision Notes

Example Calculation: pH of Sulfuric Acid Solution Calculate the pH of a 1 mol dm$^{-3}$ solution of sulfuric acid ($\text{H}_2\text{SO}_4$).

Step 1: Identify Proton Contribution:

$\text{H}_2\text{SO}_4$ is a diprotic acid, meaning it releases two $\text{H}^+$ ions per molecule.

For each mole of $\text{H}_2\text{SO}_4$, there are 2 moles of $\text{H}^+$.

Step 2: Calculate $[\text{H}^+]$:

Multiply the concentration of $\text{H}_2\text{SO}_4$ by 2.

Step 3: Calculate pH:

Example Calculation: Finding Concentration of $\text{H}_2\text{SO}_4$ from pH Calculate the concentration of sulfuric acid with a pH of 1.00.

Step 1: Calculate $[\text{H}^+]$:

Step 2: Account for Diprotic Nature:

Since sulfuric acid is diprotic, $[\text{H}^+]$ is twice the concentration of $\text{H}_2\text{SO}_4$.

Summary

• pH Calculation: $\text{pH} = -\log_{10} [\text{H}^+]$
• $[\text{H}^+]$ Calculation: $[\text{H}^+] = 10^{-\text{pH}}$
• Strong Acids: Fully dissociate, so $[\text{H}^+]$ often equals or is a multiple of the acid's concentration depending on its proticity.