The pH of saliva is normally in the range of 6.4 to 7. However, when a person is ill, the person's saliva becomes more acidic.

The pH of saliva is normally in the range of 6.4 to 7.0. However, when a person is ill, the person's saliva becomes more acidic.(a) When Marco is sick, he tests the pH of his saliva and finds that it is 5.9. What is the hydrogen ion concentration of his saliva? (Round your answer to seven decimal places.)