Acids Bases p H Section 2 6 Learning

Acids, Bases, & p. H Section 2. 6

Learning Objectives n Contrast acids and bases & discuss their properties. n Convert the hydrogen ion concentration of a solution to a p. H value. n Describe how buffers help minimize changes in p. H.

Pure Water is Neutral n Water dissociates into hydrogen ions (H+) and hydroxide ions (OH-) – One water molecule breaks down into one of each ion – H+ and OH- are equal in concentration n Since H+ and OH- are equal in concentration pure water is neutral – p. H = 7

Acids & Bases n Acid = a solution that has more hydrogen ions (H+) than hydroxide ions (OH-) – p. H < 7 – Donates H+ ions n Base = a solution that has more hydroxide ions (OH-) than hydrogen ions (H+) – p. H > 7 – Accepts H+ ions

OH– n Each p. H unit represents a tenfold change in concentration of H+ Acidic solution NEUTRAL [H+] = [OH–] Neutral solution – Logarithmic scale Figure 2. 15 Increasingly ACIDIC (Higher concentration of H+) H+ Basic solution Increasingly BASIC (Lower concentration of H+) The p. H Scale p. H scale Lemon juice; gastric juice Grapefruit juice Tomato juice Urine PURE WATER Human blood Seawater Milk of magnesia Household ammonia Household bleach Oven cleaner

p. H Indicators http: //pbskids. org/zoom/activities/sci/cabbageju iceindicato. html n Boiled cabbage creates a bluish juice that can be used to test p. H of substances – – Turns blue in bases Turns red in acids http: //www. uniregensburg. de/Fakultaeten/nat_Fak_IV/Organische_Chemie/Didaktik/Keusc h/Grafik/cabbage. gif

p. H Indicators n Other indicators: – p. H paper – Blue litmus paper http: //www. bioworld. com/images/061036. jpg § Turns red in acids – Red litmus paper http: //www. howe. k 12. ok. us/~jimaskew/lit mus. jpg § Turns blue in bases – phenolphthalein § turns pink in presence of bases http: //ull. chemistry. uakron. edu/organic_l ab/distribution/dist 13. gif

Calculating Ion Concentrations n [H+] [OH-] = 1 x 10 -14 – Ex. If [H+] = 0. 001, then what is the [OH-]? § Answer: [OH-] = 1 x 10 -11 n p. H 7 is 1 x 10 -7 n Practice Problem: What p. H is a solution that has a [H+] of 1 x 10 -10 ? – Answer: p. H 10

Buffers n Buffer = substance that resists p. H change n Accepts H+ ions when they are in excess and donates H+ ions when they are depleted n Cells need a stable p. H in order to function properly – Most cells have a p. H close to 7