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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.

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Presentation on theme: "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."— Presentation transcript:

1 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 ) = –(log 1 × log 10 –7 ) = –(0.0 + (–7.0)) = 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.

2 TEKS 10I: Define pH and use the hydrogen or hydroxide ion concentrations to calculate the pH of a solution. Sample problem: Calculating pH What is the pH of a solution with a hydrogen-ion concentration of 4.2 × 10 –10 M? (contd.)

3 TEKS 10I: Define pH and use the hydrogen or hydroxide ion concentrations to calculate the pH of a solution. Sample problem: Calculating pH Calculate the pH of a solution with a hydroxide concentration of 1.2 × 10 –3 M.

4 TEKS 10I: Define pH and use the hydrogen or hydroxide ion concentrations to calculate the pH of a solution.

5 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. H 2 O(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 –7 M. The concentration of OH – is also 1 × 10 –7 M 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.

6 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 (K w ). K w = [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 –7 M. A basic solution is one in which [H + ] is less than [OH – ]. The [H + ] of a basic solution is less than 1 × 10 –7 M. Basic solutions are also known as alkaline solutions.

7 TEKS 10I: Define pH and use the hydrogen or hydroxide ion concentrations to calculate the pH of a solution. K w = pH + pOH K w always equals 14 So.. pH + pOH = 14 You can use this equation to convert between pH and pOH

8 TEKS 10I: Define pH and use the hydrogen or hydroxide ion concentrations to calculate the pH of a solution. Sample problem: Calculating pH Calculate the pH of a solution with a pOH of 12.

9 TEKS 10I: Define pH and use the hydrogen or hydroxide ion concentrations to calculate the pH of a solution. Sample problem: Calculating pH Calculate the pOH of a solution with a pH of 9.

10 TEKS 10I: Define pH and use the hydrogen or hydroxide ion concentrations to calculate the pH of a solution. Sample problem: Calculating pH Calculate the hydrogen ion concentration of a solution with a pH of 8.5.

11 TEKS 10I: Define pH and use the hydrogen or hydroxide ion concentrations to calculate the pH of a solution. Sample problem: Calculating pH Calculate the hydrogen ion concentration of a solution with a pOH of 13.5.


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