16.1.2 Hydronium, Hydroxide, and the pH Scale

Question 1

Hydronium, Hydroxide, and the pH Scale

Answer 1

• A proton (H + ) can be solvated by varying numbers of water molecules; hydronium ion (H 3 O + ) is the simplest expression of this hydration.
• The dissociation constant of water (K w ) represents the self-ionization of water (H 2 O splitting into H + and OH – ) and has a value of 1 x 10 –14 at room temperature (25 ̊C).
• The pH of a solution is the negative logarithm of its hydronium ion concentration.

Question 2

note

Answer 2

• A proton (H + ) can be solvated by varying numbers of water molecules. For example, a proton solvated by one water molecule has the formula H 3 O + , while a proton solvated by two water molecules has the formula H 7 O 3+ .
• The hydronium ion (H 3 O + ) is the simplest expression of the hydration of a proton. H 3 O + is a more realistic expression of how a proton behaves when dissolved in water than H + .
• Water dissociates into a proton (H + ) and a hydroxide ion (OH – ). The equilibrium constant for this dissociation is the dissociation constant of water (K w ). K w has a value of 1 x 10 –14 at room temperature (25 ̊C).
• The H+ concentration of a solution can vary over more than 14 orders of magnitude. Logarithms are used to simplify the values of concentration.
• The pH of a solution is the negative logarithm of its
  hydronium ion (or proton) concentration. Low pH values indicate acidic solutions, and high pH values indicate basic solutions. While pH values are often between 0 and 14, a solution can have a negative pH or a pH between 14 and 15.
• The pOH of a solution is the negative logarithm of its
  hydroxide ion concentration. The sum of pH and pOH for a given solution is 14.

Question 3

What is the pOH of a solution if the hydroxide ion concentration is 1.7 × 10−4 M?

Answer 3

3.77

Question 4

What is the pOH if the hydronium ion concentration is 3.3 × 10−8 M?

Answer 4

6.52

Question 5

Which of the following pH values indicates a basic solution?

Answer 5

9

Question 6

Which of the following is the most acidic?

Answer 6

pH = 4

Question 7

What is the [OH − ] in pure water at 25°C?

Answer 7

1.0 × 10^−7 M

Question 8

What is the pH of a solution with a [H3O+ ] of 6.3 × 10^−11 M?

Answer 8

10.20

Question 9

A student adds 1.00 × 10^−8 moles of HCl to a liter of solution. The resulting solution will be ____.

Answer 9

acidic

Question 10

What is the pH of a solution with a [H3O+ ] of 1.9 × 10^−5 M?

Answer 10

4.72

Question 11

What is the Kw for pure water at 25°C?

Answer 11

1 × 10^−14

Question 12

What is the [H3O+ ] in a solution with a pH of 9.50?

Answer 12

3.2 × 10^−10 M