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Chapter 25

Chapter 25. Lesson 2 Strengths of Acids and Bases. -. -. +. +. Strong and Weak Acids and Bases. The strength of an acid or base depends on how many acid or base particles dissociate into ions in water. Strong Acid/Base 1 00% ions in water strong electrolyte

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Chapter 25

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  1. Chapter 25 Lesson 2 Strengths of Acids and Bases

  2. - - + + Strong and Weak Acids and Bases • The strength of an acid or base depends on how many acid or base particles dissociate into ions in water. • Strong Acid/Base • 100% ions in water • strong electrolyte • HCl, HNO3, NaOH, LiOH • Weak Acid/Base • few ions in water • weak electrolyte • HC2H3O2, NH3

  3. Strong and Weak Acids • Equations describing dissociation can be written in two ways. • In strong acids, such as HCl, nearly all the acid dissociates. • This is shown by writing the equation using a single arrow pointing toward the ions that are formed.

  4. Strong and Weak Acids • Equations describing the dissociation of weak acids, such as acetic acid, are written using double arrows pointing in opposite directions. • This means that only some of the CH3COOH dissociates and the reaction does not go to completion.

  5. Strong and Weak Bases • A strong base dissociates completely in solution • The following equation shows the dissociation of sodium hydroxide, a strong base.

  6. Strong and Weak Bases • This dissociation of ammonia, which is a weak base, is shown using double arrows to indicate that not all the ammonia ionizes. It only produces a few ions in water.

  7. pH of a Solution • The pH of a solution is a measure of the concentration of H+ ions in it. • The greater the H+ concentration is, the lower the pH is and the more acidic the solution is. • The pH measures how acidic or basic a solution is.

  8. pH Scale • pH • a measure of the concentration of H3O+ ions in solution • measured with a pH meter or an indicator with a wide color range 14 0 7 NEUTRAL • INCREASING • BASICITY INCREASING ACIDITY

  9. pH Scale pH of Common Substances

  10. Strength and Concentration • In contrast, the terms dilute and concentrated are used to indicate the concentration of a solution, which is the amount of acid or base dissolved in the solution.

  11. Strength and Concentration • It is possible to have dilute solutions of strong acids and bases and concentrated solutions of weak acids and bases

  12. Blood pH • In order to carry out its many functions properly, the pH of blood must remain between 7.0 and 7.8. • The main reason for this is that enzymes, the protein molecules that act as catalysts for many reactions in the body, cannot work outside this pH range.

  13. Blood pH • Your blood contains compounds called buffers that enable small amounts of acids or bases to be absorbed without harmful effects. • Buffers are solutions containing ions that react with additional acids or bases to minimize their effects on pH.

  14. ConcepTest • Which of the following "molecular" pictures best represents a concentrated solution of the weak acid HA? A B

  15. ConcepTest • Is the following statement TRUE or FALSE? • A strong acid has a lower pH than a weak acid. • TRUE - Strong/weak refers to amount of ionization whereas pH refers to concentration of H+.

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