Question

Which of these solutions is acidic?

Answer 1

Answer:

Option a is a solution acidic ([OH⁻] = 7.0x10⁻⁹ M).

Explanation:

To know if a solution is acidic we need to calculate the pH and it must be lower than 7. A value of pH equal to 7 is a neutral solution and a solution with a pH value higher than 7 is a basic solution.

a. For the [OH⁻] = 7.0x10⁻⁹ M we have:

$pOH = -log[OH^{-}] = -log(7.0 \cdot 10^{-9}) = 8.15$

Now, the pH is:

$pH + pOH = 14$

$pH = 14 - pOH = 14 - 8.15 = 5.85$

This solution is acidic (pH < 7)

b. [H₃O⁺] = 8.5x10⁻⁸ M

$pH = -log(8.5 \cdot 10^{-8}) = 7.07$

This is not an acidic solution. Is a neutral one (pH around to 7).

c. [OH⁻] = 2.5x10⁻⁶ M

$pOH = -log[OH^{-}] = -log(2.5 \cdot 10^{-6}) = 5.60$

Then, the pH is:

$pH = 14 - pOH = 14 - 5.60 = 8.40$

Hence, this is not an acidic solution. It is basic (pH > 7).    

Therefore, option a is a solution acidic ([OH⁻] = 7.0x10⁻⁹ M).

I hope it helps you!