Final answer:
To find the pH of a solution with a concentration of 6.8 x 10^-4 molar H3O+, use the formula pH = -log[H3O+]. The result should have two significant figures after the decimal, in line with the two significant figures in the concentration value.
Step-by-step explanation:
The pH of a solution can be calculated using the concentration of hydronium ions (H3O+) with the formula: pH = -log[H3O+].
For a concentration of 6.8 x 10^-4 molar H3O+, the pH is calculated as follows:
pH = -log[6.8 x 10^-4]
Using a scientific calculator to find the logarithm, the pH would be computed with care to significant figures.
With the provided concentration 6.8 having two significant figures, the pH value should also have two significant figures after the decimal.
However, the exact pH value was not calculated as part of the provided examples.
Correct calculation should be done by the student using a scientific calculator.