1. The Chemistry of Acids and Bases Thornburg 2014

2. Objectives Define the following: –Acids –Bases –The pH scale compare/ contrast properties of acids and bases Describe common uses of acids and bases Explain and write equations for the chemical reactions that occur between acids and bases Thornburg 2014

3. Acids Acid – a chemical which easily “donates” (loses) a hydrogen ion (H+) when placed in an aqueous solution Examples: Carbonic Acid Hydrochloric Acid Stomach Acid Battery Acid Thornburg 2014

4. Properties of Acids Cause foods to taste tart or sour (vinegar – contains acetic acid) React with metals to produce hydrogen gas React with a base to produce an ionic salt and water Found in many citrus foods Form electrolytes when placed into water Thornburg 2014

5. Dissociation of an acid in water Example: HCl (g) H + (aq) + Cl - (aq) An acid will dissociate (break apart) into H + ions and negative ions when placed into waterAn acid will dissociate (break apart) into H + ions and negative ions when placed into water H2OH2OH2OH2O Thornburg 2014

6. When the acid dissociates into H + ions and negative ions, some of the water molecules will bond with the H + ions and form a Hydronium ion (H 3 O + )When the acid dissociates into H + ions and negative ions, some of the water molecules will bond with the H + ions and form a Hydronium ion (H 3 O + ) The strength of Acids are actually measured by the amount of Hydronium ions they form when placed in waterThe strength of Acids are actually measured by the amount of Hydronium ions they form when placed in water Thornburg 2014

7. Bases Base – a chemical which easily “accepts” (gains) a hydrogen ion (H+) when placed in an aqueous solution Examples: Potassium Hydroxide Magnesium Hydroxide Ammonia Thornburg 2014

8. Properties of Bases Taste bitter Feel slippery Will form electrolytes when placed in aqueous solutions Found in many soaps and household cleaners Thornburg 2014

9. Dissociation of a base in water Example: NaOH (s) Na + (aq) + OH - (aq) A base will dissociate (break apart) into OH - ions and positive ions when placed into waterA base will dissociate (break apart) into OH - ions and positive ions when placed into water The OH - ions will then “accept” Hydrogen ionsThe OH - ions will then “accept” Hydrogen ions H2OH2OH2OH2O Thornburg 2014

10. Acid – Base Chemical Reactions A neutralization reaction will occur when an acid and a base are mixed in an aqueous solution: Acid + Base Salt + Water HCl (aq) + NaOH (aq) NaCl (s) + H 2 O HNO 3 (aq) + Mg(OH) 2 (aq) Mg(NO 3 ) 2 (s) + H 2 O Thornburg 2014

11. The pH Scale Measures the relative strength of acids and bases Range is from 0 – 14 0 = strongest acids 7 = neutral 14 = strongest bases Thornburg 2014

12. The pH scale is logarithmic A solution with a pH value of 4 has 10 times as many H+ ions as a solution with a pH value of 5 A solution with a pH value of 3 has 100 times as many H+ ions as a solution with a pH value of 5 Thornburg 2014

13. What is a BUFFER ? A buffer solution is a solution that will resist extreme changes in pH when mixed with a strong acid or a strong base A buffer is usually a mixture of a weak acid and a weak base Thornburg 2014

14. Summary Acids = donate H+ ions Taste tart/ sour, found in many foods Bases = accept H+ ions Found in soaps/ cleaning products Acid + Base = salt + water The pH scale measures the strength of acids and bases Thornburg 2014