Lime is added to a lake to neutralize the effects of acid rain. The pH value of the lake water rises from 4 to 7. What is the change in concentration of H+ ions in the
lake water?

The change in concentration of H+ ions is -9.99×10⁻⁵

Explanation:

When pH rises, we talk about neutralization and, there is a decline in proton's concentration.

pH lower than 7 is acid

pH higher than 7 is basic

Protons are neutralized by hydroxides to make water as this:

H₃O⁺   +  OH⁻  ⇄   H₂O

pH = - log [H₃O⁺]

[H₃O⁺] = 10^-pH

In conclussion: [H₃O⁺]₁ = 10⁻⁴ → 1×10⁻⁴

[H₃O⁺]₂ = 10⁻⁷ → 1×10⁻⁷

1×10⁻⁷- 1×10⁻⁴

The change in concentration of H+ ions is -9.99×10⁻⁵