Answer:
1. 6.34.
2. 6.3 x 10⁻¹¹ M H₃O⁺ and 1.6 × 10⁻¹⁰ M OH⁻.
3. 7.58.
4. 4.38.
5. True.
6. True.
Explanation:
<em>1. What is the pH of a solution with a 2.20 × 10⁻⁸ M hydroxide ion concentration?</em>
<em>∵ [H₃O⁺][OH⁻] = 10⁻¹⁴.
</em>
[OH⁻] = 2.20 × 10⁻⁸ M.
∴ [H₃O⁺] = 10⁻¹⁴/[OH⁻] = 10⁻¹⁴/(2.20 × 10⁻⁸ M) = 4.54 × 10⁻⁷ M.
∵ pH = - log[H₃O⁺]
<em>∴ pH = - log(4.54 × 10⁻⁷ M) = 6.34.</em>
<em></em>
<em>2. What are the concentrations of hydroxide and hydronium ions in a solution with a pH of 10.2?</em>
∵ pH = - log[H₃O⁺]
∴ 10.2 = - log[H₃O⁺].
∴ log[H₃O⁺] = - 10.2.
<em>∴ [H₃O⁺] = 6.31 x 10⁻¹¹ M ≅ 6.3 x 10⁻¹¹ M.</em>
∵ [H₃O⁺][OH⁻] = 10⁻¹⁴.
[H₃O⁺] = 6.31 x 10⁻¹¹ M.
∴ [OH⁻] = 10⁻¹⁴/[H₃O⁺] = 10⁻¹⁴/(6.31 x 10⁻¹¹ M) = 1.58 × 10⁻⁴ M ≅ 1.6 × 10⁻¹⁰ M.
<em>So, the right choice is: 6.3 x 10⁻¹¹ M H₃O⁺ and 1.6 × 10⁻¹⁰ M OH⁻.</em>
<em></em>
<em>3. A solution at 25 degrees Celsius has a pOH of 6.42. What is the pH of this solution?</em>
∵ pH + pOH = 14.
∵ pOH = 6.42.
<em>∴ pH = 14 - pOH = 14 - 6.42 = 7.58.</em>
<em></em>
<em>4. What is the pH of a solution with a concentration of 4.2 × 10⁻⁵ M H₃O⁺?</em>
∵ pH = - log[H₃O⁺]
∵ [H₃O⁺] = 4.2 × 10⁻⁵ M.
<em>∴ pH = - log(4.2 × 10⁻⁵ M) = 4.376 ≅ 4.38.</em>
<em></em>
<em>5. Water is an amphoteric substance because it can receive and donate hydrogen ions. True False</em>
A Brønsted-Lowry acid is any species that is capable of donating a proton H⁺.
A Brønsted-Lowry base is any species that is capable of accepting a proton, which requires a lone pair of electrons to bond to the H⁺.
Water is amphoteric, which means it can act as both a Brønsted-Lowry acid and a Brønsted-Lowry base.
<em>So, the answer is: True.</em>
<em></em>
<em>6. The concentration of hydronium ions is greater than 1 × 10⁻⁷ for basic solutions. True False</em>
For a solution to be acidic, The concentration of hydronium ions is smaller than 1 × 10⁻⁷, that pH of the solution will be lower than 7.
For a solution to be basic, The concentration of hydronium ions is greater than 1 × 10⁻⁷, that pH of the solution will be higher than 7.
<em>So, the answer is: True.</em>
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