Acids, Bases, and Salts

Electrolytes An electrolyte is a substance that dissociates when dissolved in water. (Nonelectrolytes do not dissociate.) These compounds conduct electricity based on this dissociation. To dissociate means to separate into ions in solution. Acids, bases, and salts (ionic compounds) are all electrolytes.

Strong vs. Weak Electrolytes Strong electrolytes fully dissociate in water. (ex. Ionic compounds, strong acids, strong bases) Weak electrolytes only partly dissociate in water. (ex. Weak acids and weak bases) Nonelectrolytes do not dissociate in water. (nonpolar covalent compounds)

Write an equation for the dissociation of magnesium nitrate in water.

Write an equation for the dissociation of the weak acid, HF, in water.

Acids and Bases Acids, bases, and salts make up compounds known as electrolytes. Arrhenius acids – substances that ionize in water to produce the hydrogen ion, H+. Arrhenius bases – substances that ionize in water to produce the hydroxide ion, OH-.

HCl(g) → H+(aq) + Cl-(aq) NaOH(cr) → Na+(aq) + OH-(aq) Dissociation – already formed ions separate Ionization – neutral molecules react with water to form charged ions

Strength of Acids and Bases Strength of acids and bases depends on how completely they ionize in water - the strongest acids and bases fully ionize in water while weak acids and bases only ionize slightly

Strong acids (Know these)– HCl, HBr, HI are all strong, while all other binary acids are weak As a rule, all acids with at least two more oxygens than hydrogens are strong (H2SO4, HNO3,HClO4) Strong bases – Hydroxides of the Groups I and II elements except for Be are all strong.

Acid Nomenclature In general, names of acids will begin with hydrogen. If the anion does not contain oxygen, the acid begins with hydro and ends in –ic HCl = hydrochloric acid HBr = HCN =

Acids containing oxygen If the acid contains oxygen, the acid does not have hydro at the start and either ends in ic or ous. If the anion ends in –ate use –ic HNO3 = nitric acid If the anion ends in –ite use –ous H2SO3 = sulfurous acid

What is the formula for hydroiodic acid? HI HI2 H2I HIO3

What is the formula for hydrocyanic acid? H3N HN HCN HSCN

What is the formula for phosphoric acid? H3PO3 H3PO4 HPO4 HPO3

What is the formula for sulfurous acid? H2SO3 H2SO4 H2S HS2

What is the name of HNO2? Hydronitric acid Hydronitrous acid

What is the name of HCl? Hydrochloric acid Hydrochlorous acid

What is the name of HClO4? Hydrochloric acid Chlorous acid Perchloric acid

Relative Strength of Acids and Bases

Conjugate Acids and Bases The strength of conjugate acids and bases are inversely proportional.

Kw Kw for water is based on the equation: 2H2O (l) -> OH- (aq) + H3O+ (aq) Kw = [OH-][H3O+] = 10-14 Therefore, if you know either hydroxide or hydronium concentrations, you can solve for the other.

pH scale pH is the measure of the concentration of hydronium ion in a water solution pH = -log[H30+] Scale goes from 0 to 14. 0 to 7 is acidic, 7 is neutral, 7 to 14 is basic

pH – log based Every increase of 1 on the pH scale changes the concentration by a power of 10. How much stronger is a substance with a pH of 4 vs a pH of 6?

pOH scale pOH is the measure of the concentration of hydroxide ion in a water solution pOH = -log[0H-] Also, pH + pOH =14

Neutralization Reaction A neutralization reaction occurs when and acid and a base react to form water and a salt. Acid + Base -> Water + Salt ***When the base has a CO32- ion, CO2 is also produced.

Titrations Titrations are a quantitative lab technique that helps identify an unknown concentration of acid or base by titrating it against a titrant, or known acid or base concentration.

Titration Method Add an accurately measured volume of unknown acid (or base) to an Erlenmeyer flask Put 2-3 drops of phenolphthalein indicator to the unknown solution. Start adding the titrant and continue until the solution turns pink and stays pink.

Titration Tips Record the unknown’s volume by subtracting the ending vs. starting amount from buret (use the right amount of sig figs). You can add the titrant quickly at first but once it starts turning pink, swirl the flask and start adding more slowly. Swirl after each drop towards the equivalence point.