Acid rain (see Chemistry in the Environment box in Section 5.9) over the Great Lakes has a pH of about 4.5. Calculate the [H30+] of this rain and compare that value to the [H30+] of rain over the West Coast that has a pH of 5.4. How many times more concentrated is the acid in rain over the Great Lakes?
Solution: Here, we are going to calculate the concentration of hydronium ion of rain over the Great Lakes and compare it with that over the West Coast.
Step1:
pH is the negative logarithm to base 10 of hydrogen ion concentration.
pH = - log[H3O+ ]
Step2:
Given, pH of the acid rain over the Great Lakes = 4.5
pH = - log[H3O+]
Therefore, [H3O+] = 10-pH
= 10-4.5
= 3.16 x 10-5
Again, pH of the rain over the West Coast = 5.4
pH = - log[H3O+]
Therefore, [H3O+] = 10-pH
= 10-5.4
= 3.98 x 10-6
Step3:
Thus, the concentration of hydronium ion is higher in the acid rain over the Great Lakes.
Now, [H3O+] over Great Lakes / [H3O+] over the West Coast = (3.16 x 10-5) / (3.98 x 10-6)
= 7.93
= 8 (approx.)
Thus, the acid in rain over the Great Lakes is approximately 8 times more concentrated.
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