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pH Scale

## pH Scale

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1. pH

2. pH Scale • Logarithmic scale. • Measures the concentration of hydrogen ions [H+] in a solution. • Range from 0-14. • NEUTRAL, pH=7. (pure water) • BASE, pH > 7. (ocean water, milk of magnesia, baking sodea) • ACID, pH < 7. (stomach acid/HCl, vinegar, soft drinks)

3. pH Scale

4. Log Scale Relationship

5. Let’s take a look at water • 2H2O H3O+ + OH- • [H3O+][OH-]= 1x10-14M2 • [H3O+]= 1x10-7M • [OH-]= 1x10-7M • Kw= 1x10-14M2

6. Example 1 • An acid is added to water and gives a hydroxide ion concentration [OH-] of 1.0x10-12M. What is the hydrogen ion concentration [H+] ?

7. How do we measure the pH of a solution? • Acid-base indicators (ex. litmus paper) • pH meter

8. Equations • pH = -log[H+] • pOH = -log[OH-] • pH + pOH = 14 • [H+][OH-] = 1x10-14 M2

9. Example 2: What is the pH of a solution with a hydrogen ion concentration of 1x10-4M ? Is this solution acidic or basic ?

10. Example 3: What is the hydrogen ion concentration of a solution with a pH of 11 ? Is this solution acidic or basic ?

11. Example 4: Calculate the [H+] and [OH-] of a vinegar solution with a pH of 2.5.

12. Now, you try…… • 1) [H3O+] = 1.5x10-6M. Find the pH. • 2) A solution’s pH is 3.72. What are the [H3O+] and [OH-] concentrations in the solution?

13. Thought Question • When an acid is added to a beaker of water, what happens to the [H3O+] and [OH-] in the solution? Why? What happens to the pH? Why?

14. Acids and Bases: an Introduction

15. Acids • Sour Taste • Electrolytes • Identified by the presence of H+ ions (Arrhenius). • Proton (H+) donor (Bronsted-Lowry). • Common Acids: vinegar, citric acid, sulfuric acid, hydrochloric acid.

16. Bases • Bitter taste • Slippery • Like acids, they are electrolytes • Identified by the presence of OH- ions (Arrhenius). • Proton (H+) acceptor (Bronsted-Lowry).

17. Strength of Acids and Bases • Based on the concentration of H+ or OH- ions in a solution. • Strong Acids/Bases: completely dissociate into ions in a solution. • Weak Acids/Bases: do NOT completely dissociate into ions in a solution.

18. HNO3 + NH3 NH4+ + NO3- • Identify the Acid and Base

19. Stronger the acid, weaker its conjugate base. • Stronger the base, weaker its conjugate acid.

20. Neutralization ACID + BASE SALT + WATER

21. Nomenclature

22. Example 1: HBr • Write name

23. Now you try, HCl • Write name.

24. Example 2: Hydrofluoric acid • Write chemical formula

25. Now you try, hydriodic acid.

26. Example 3: H2SO4 • Write the name.

27. Example 4: HClO2 • Write the name.

28. Try: • HClO3 • HClO • HClO4

29. Base Nomenclature • Name of cation, name of anion/hydroxide • Ex. NaOH

30. Tomorrow…. • Briefly brainstorm how we measure the amount of hydrogen ions in a solution? How can we quickly measure the acidity or basicity of a solution?