Acids, Bases, and pH

Acids and Bases Acids produce H + ions which react with water to form hydronium (H 3 O + ) ions Bases produce OH - ions

Macroscopic properties of acids and bases Taste and feel – Acids taste sour (lemon juice, vinegar) – Bases taste bitter – Bases are slippery (soap)

Acids react with bases – the reaction of acids and bases are central to the chemistry of living systems, the environment, and many important industrial processes

Litmus test and other color changes – Indicators change colors in the presence of an acid or a base – Litmus: acid = red, base = blue

Submicroscopic behavior of acids Hydronium ion formation HCl + H 2 O  H 3 O + + Cl - HNO 3 + H 2 O  H 3 O + + NO 3 -

Acidic hydrogen atoms – Reaction of acid with water is a transfer of a hydrogen ion from an acid to a water molecule – Any hydrogen that can be transferred to water is called an acidic hydrogen – It is possible for acids to have more than one acidic hydrogen

Acids are electrolytes – Substance that dissolve in pure water to form ions & conduct electricity – Not all acids conduct electricity equally well Strong acids conduct electricity better than weak acids

Submicroscopic behavior of bases Hydroxide ion formation can happen two ways Simple bases: NaOH  Na + + OH - Bases that accept H + : NH 3 + H 2 O  NH 4 + +OH -

Bases are electrolytes – Strong bases conduct electricity better than weak bases

Macroscopic-Submicroscopic Acid- Base Connection The properties of acids and bases are determined by the submicroscopic interactions between the acid or base and water

Strengths of Acids and Bases Strong acids and bases ionize completely while weak acids and bases ionize only partially

Strong Bases A base that completely dissociates into ions when dissolved in water Ionic compounds that contain hydroxide ions NaOH  Na + + OH -

Strong Acids An acid that completely ionizes in water HCl + H 2 O  H 3 O + + Cl -

Weak Acids An acid that only partially ionizes in solution Usually when acidic hydrogen is bonded to an oxygen H 2 CO 3 + H 2 O  H 3 O + + CO H 2 CO 3

Weak Bases Only partially ionize in solution NH 3 + H 2 O  NH OH - + NH 3 + H 2 O

Weak is not insignificant Most acids and bases are classified as weak Most of the acid-base chemistry in living systems occurs between weak acids and weak bases

Strength is not concentration Weak & strong compare strength Dilute and concentrated compare concentration Combination of strength and concentration determine the behavior of solution

The pH Scale A mathematical scale in which the concentration of H + ions in a solution is expressed as a number from 0 – 14

Interpreting the pH scale pH < 7 = acidic pH = 7 = neutral pH > 7 = basic Each unit of pH represents a power of 10 – Something with pH of 2 is 10 times more acidic than something with a pH of 3

pH = -log [H + ] What is the pH of solutions having the following ion concentrations? 1.[H + ] = 1.0 x M 2.[H + ] = 3.0 x M

Relating H + and OH - ion concentration

pOH = -log [OH - ] What is the pOH of a solution having the following ion concentration? 1.[OH - ] = 1.0 x M 2.[OH - ] = 6.5 x M

pH + pOH = 14 What is the pOH of a solution whose pH is 5? What is the pH of a solution whose [OH - ] = 4.0 x M

Calculate the pH and pOH of the following solutions: 1.[H+] = M 2.[OH-] = M