Question

Use a scientific calculator to calculate [H+] for the following pH values:

7 (a neutral solution)

5.6 (unpolluted rainwater)

3.7 (first acid rain sample in North America)

How many times higher is the concentration of H+ in the Hubbard Brook sample than in unpolluted rainwater?

Answer 1

1. 7 (a neutral solution)

Answer: 10-7= 0.0000001 moles per liter

2. 5.6 (unpolluted rainwater)

Answer: 10-5.6 = 0.0000025 moles per liter

3. 3.7 (first acid rain sample in North America)

Answer: 10-3.7 = 0.00020 moles per liter

The concentration of H+ in the Hubbard Brook sample is 0.00020/0.0000025, which is 80 times higher than the H+ concentration in unpolluted rainwater.

Explanation: -

Answer 2

pH = 7 ⇒ [H⁺] = 1.0x10⁻⁷ M

pH = 5.6 ⇒ [H⁺] = 2.5x10⁻⁶ M

pH = 3.7 ⇒ [H⁺] = 2.0x10⁻⁴ M

H⁺ concentration in the Hubbard Brook sample is 80 times higher than in unpolluted rainwater.

Step-by-step explanation:

To answer this problem we need to keep in mind the definition of pH:

• pH = -log[H⁺]

Meaning that after isolating [H⁺] we're left with:

• [H⁺] =
  `10^(-pH)`

Now we proceed to calculate [H⁺] for the given pHs:

• pH = 7 ⇒ [H⁺] =
  `10^(-7)` = 1.0x10⁻⁷ M

• pH = 5.6 ⇒ [H⁺] =
  `10^(-5.6)` = 2.5x10⁻⁶ M

• pH = 3.7 ⇒ [H⁺] =
  `10^(-3.7)` = 2.0x10⁻⁴ M

Finally we calculate how many times higher is [H⁺] when pH = 3.7 than when pH = 5.6.

• 2.0x10⁻⁴ / 2.5x10⁻⁶ = 80