TEKS 10I: Define pH and use the hydrogen or hydroxide ion concentrations to calculate the pH of a solution. How is pH defined? • The pH of a solution is the negative logarithm of the hydrogen-ion concentration . The pH may be represented mathematically, using the following equation: pH = –log[H + ] In pure water or a neutral solution, [H + ] = 1 × 10 –7 M, and the pH is 7. pH = –log(1 × 10 –7 ) = 7.0 • If the [H + ] of a solution is greater than 1 × 10 – 7 M, the pH is less than 7.0. If the [H + ] of the solution is less than 1 × 10 –7 M, the pH is greater than 7.0.
Transcript
TEKS 10I: Define pH and use the hydrogen or hydroxide ion concentrations to calculate the pH of a solution.
How is pH defined?How is pH defined?• The pH of a solution is the negative logarithm of the
hydrogen-ion concentration. The pH may be represented mathematically, using the following equation:
pH = –log[H+]
In pure water or a neutral solution, [H+] = 1 × 10–7M, and the pH is 7.
pH = –log(1 × 10–7)
= 7.0• If the [H+] of a solution is greater than 1 × 10–7M, the pH is
less than 7.0. If the [H+] of the solution is less than 1 × 10–
7M, the pH is greater than 7.0.
TEKS 10I: Define pH and use the hydrogen or hydroxide ion concentrations to calculate the pH of a solution.
ChemSaver p 40ChemSaver p 40Calculate the pH of the following acids:
pH= -log [H+]
[H+] = 3.4 x 10-5 M
The molarity of the acid is 6.5 x 10-4 M
TEKS 10I: Define pH and use the hydrogen or hydroxide ion concentrations to calculate the pH of a solution.
What is the pH of a solution with a hydrogen-ion concentration of
4.2 × 10–10M?
(contd.)
TEKS 10I: Define pH and use the hydrogen or hydroxide ion concentrations to calculate the pH of a solution.
pH and pOH ScalepH and pOH Scale
TEKS 10I: Define pH and use the hydrogen or hydroxide ion concentrations to calculate the pH of a solution.
ChemSaver p 39ChemSaver p 39
acidic
basic acidic
basic
neutral neutral
TEKS 10I: Define pH and use the hydrogen or hydroxide ion concentrations to calculate the pH of a solution.
TEKS 10I: Define pH and use the hydrogen or hydroxide ion concentrations to calculate the pH of a solution.
ChemSaver p 40ChemSaver p 40Calculate the pOH of the following bases:
pOH= -log [OH-]
[OH-] = 1 x 10-9 M
The molarity of the base is 3.8 x 10-10 M
TEKS 10I: Define pH and use the hydrogen or hydroxide ion concentrations to calculate the pH of a solution.
How are [H+] and [OH–] related in an aqueous solution?
How are [H+] and [OH–] related in an aqueous solution?
• The reaction in which water molecules produce ions is called the self-ionization of water. This reaction can be written as a simple dissociation.
H2O(l) H⇄ +(aq) + OH–(aq)
• The self-ionization of water occurs to a very small extent. In pure water at 25°C, the concentration of hydrogen ions is only 1 × 10–7M. The concentration of OH– is also 1 × 10–7M because the numbers of H+ and OH– ions are equal in pure water.
• Any aqueous solution in which [H+] and [OH–] are equal is a neutral solution.
TEKS 10I: Define pH and use the hydrogen or hydroxide ion concentrations to calculate the pH of a solution.
• For aqueous solutions, the product of the hydrogen-ion concentration and the hydroxide-ion concentration equals 1.0 10–14.
[H+] [OH–] = 1.0 10–14
• This equation is true for all dilute aqueous solutions at 25°C. The product of the concentrations of the hydrogen ions and the hydroxide ions in water is called the ion-product constant for water (Kw).
Kw = [H+] × [OH–] = 1.0 × 10–14
• A solution in which [H+] is greater than [OH–] is an acidic solution. In acidic solutions, the [H+] is greater than 1 × 10–7M.
• A basic solution is one in which [H+] is less than [OH–]. The [H+] of a basic solution is less than 1 × 10–7M. Basic solutions are also known as alkaline solutions.
TEKS 10I: Define pH and use the hydrogen or hydroxide ion concentrations to calculate the pH of a solution.
Kw = pH + pOH
Kw always equals 14
So..
pH + pOH = 14You can use this equation to convert
between pH and pOH
TEKS 10I: Define pH and use the hydrogen or hydroxide ion concentrations to calculate the pH of a solution.
ChemSaver p 40ChemSaver p 40Calculate the pH or the pOH from the given, then tell if the substance is acidic, basic, or neutral.
pH + pOH = 14
pH = 8 pOH = _______ (acidic/ basic/ neutral)
pH = ______ pOH = 2 (acidic/ basic/ neutral)
TEKS 10I: Define pH and use the hydrogen or hydroxide ion concentrations to calculate the pH of a solution.
