Question

Over a number of years the average pH of a stream changes from a pH of 6.9 to a pH of 5.9 due to acid rain. Which statement is true about the pH of the stream?

• A. The pH of the stream now is one times more acidic than it was years ago
• B. The stream now has 10 times more hydroxide ions than it did years ago
• C. The pH of the stream is now 10 times more acidic than it was years ago
• D. The stream is more basic now than it was years ago
• E. The concentration of hydronium ion in the stream has decreased over the years

Answer 1

The correct option is C The pH of the stream is now 10 times more acidic than it was years ago

Over a number of years the average pH of a stream changes from a pH of 6.9 to a pH of 5.9 due to acid rain. The pH of the stream is now 10 times more acidic than it was years ago.
Years ago, the pH was 6.9. The present day pH is 5.9. The change in pH is
$=\Delta pH=5.9-6.9=-1$
The corresponding change in hydrogen ion concentration is:
${10}^{-\Delta pH}={10}^{-(-1)}=10$