Question

Acid rain over the Great Lakes has a pH of about 4.5 while acid rain over the West Coast has a pH of about 5.4. The lakes are then acidified by rainfall but are after treated through a neutralizing process called liming. This process involves adding limestone to the lake in large quantities.

a. What are the [H3O+] concentrations in each lake?
b. How many more times concentrated is the acid rain over the Great Lakes?

Please show all work/explain...I'd really like to understand how to get to the answer. THANKS

Answer 1

a)

pH = - log₁₀ [H₃O⁺] (where [H₃O⁺] is the concentration of hydronium ions in Mol/Litre)

or, log₁₀ [H₃O⁺] = -pH

or, [H₃O⁺] = 10^(-pH)

• For Great Lake, [H₃O⁺] = 10^{(- 4.5)} mol/litre

             Or, [H₃O⁺] = 3.162 * 10^-5 mol/litre

• For West Coast, [H₃O⁺] = 10^{(- 5.4)} mol/litre

             Or, [H₃O⁺] = 3.981 * 10^-6 mol/litre

b)

The concentrations are in the order of 10^-5 for Great Lake and 10^-6 for West Coast (clearly, the factors 3.162 and 3.981 don’t have much saying in the numerical values of these orders).

Now, 10^-6 * 10 = 10^-5

Thus we can see, the acid rains over the Great Lake are almost 10 times more concentrated than that over the West Coast.

To be precise, it's (3.162 * 10^-5 mol/litre) / (3.981 * 10^-6 mol/litre) = .794 * 10 = 7.94 times more concentrated than the latter.