Strengths of Acids and Bases SCH 11U

Ionization Acid molecules ionize in water; the neutral molecule breaks apart into charged ions HCl  H+ + Cl – H2SO4  2H+ + SO42-

Degree of Ionization Some acids tend to ionize to a greater degree than others Strong acids completely ionize in water into their ions 100% H Cl H+ + Cl-

Degree of Ionization Weak acids only partially ionize in water to form only a few ions. The majority of the molecules remain as neutral ions. 1% C2H3O2 C2H3O2 H H+ +

Dissociation Bases dissociate in water into their ions Strong bases dissociate completely NaOH  Na+ + OH- Weak bases only partially dissociate Ca(OH)2  Ca2+ + 2OH-

Concentration The concentration of an acid or base refers to the amount of acid or base molecules in the total solution. c (mol/L) = n (mol) v (L) Dilute acids have a relatively small amount of solute per volume of solution Concentrated acids have a relatively high amount of solute per volume of solution

Concentration Concentrated Dilute

Concentration Concentrated Dilute

Strength Strength of an acid or base depends on the hydrogen or hydroxide ion concentration. The higher the hydrogen ion, concentration the stronger the acid > [H+] stronger acid The higher the hydroxide ion, concentration the stronger the base > [OH-] stronger base

Ion Concentration Strong acids and bases ionize or dissociate completely If you know the concentration of the acid we can predict the concentration of the ions using the mole ratio HCl  H+ + Cl – 0.25 mol/L ?

Ion Concentration HCl  H+ + Cl – 0.25 mol/L ?

Ion Concentration H2SO4  2H+ + SO42- 0.125 mol/L ?

Ion Concentration NaOH  Na+ + OH- 0.36 mol

Measuring Strength pH stands for power of hydrogen pH scale is a measure of acidity of a substance It is a simple way to express the hydrogen ion concentration

pH Scale Scale ranging from 0-14 0-7 acidic, 7-14 basic, 7 neutral Each number is a ten-fold (10X) jump in concentation ie) pH 3 is 10 times more acidic than pH 4

pH Calculations Use the following equation to find a pH if given a concentration: pH = - log [H+]

pH Calculations [H+] = 1.0 x 108 pH = [H+] = 2.5 x 105 pH =

[H+] Calculations Use the following relationship to determine the hydrogen ion concentration if given pH [H+] = 10-pH [H+] = antilog (- pH)

[H+] Calculations pH = 5 [H+] = pH = 2.3 [H+] = pH = 7.9 [H+] =

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