Final answer:
The pH of a solution is calculated using the formula pH = -log [H3O+]. The pH represents the acidity or alkalinity of the solution. To reverse the process and find the hydronium ion concentration from a known pH, the formula [H3O+] = 10^-pH is used.
Step-by-step explanation:
The formula for calculating pH based on the concentration of hydronium ions is pH = -log [H3O+]. The acidity or alkalinity of a solution is determined by the concentration of hydronium ions present. To find the pH from a known hydronium ion concentration, you take the negative logarithm of the concentration. For instance, if you have a hydronium ion concentration of 3.96 × 10-5 M, then the pH is calculated as follows:
pH = -log[3.96 × 10-5] = 4.4023
Note on significant figures: The number of decimal places in the pH value should reflect the number of significant figures in the given hydronium ion concentration.
To calculate the hydronium ion concentration from pH, you would do the inverse operation, taking the antilog (or inverse log) of the negative pH:
[H3O+] = 10-pH