Final answer:
To find the pH of seawater with a hydronium ion concentration of 6.30957 x 10^-9 M, use the formula pH = -log[H3O+], which gives a pH of approximately 8.2.
Step-by-step explanation:
To calculate the pH of a seawater sample when given the hydronium ion concentration (H3O+), you use the formula pH = -log[H3O+]. The given hydronium ion concentration is 6.30957 x 10^-9 M. Thus, the pH calculation would be:
pH = -log(6.30957 x 10^-9)
After performing the calculation, you should find the pH to be approximately 8.2, as higher pH values above 7 indicate a basic solution, while lower values indicate an acidic solution.