260 likes | 407 Views
Unit 11. Acids and Bases. Acid vs Base. All aqueous solutions contain H + and OH - ions. Relative amounts determine whether the solution is acid, base, or neutral Acid soln – more H + (Hydronium ion) Basic soln- more OH - Neutral- equal amounts of each.
E N D
Unit 11 Acids and Bases
Acid vs Base • All aqueous solutions contain H+ and OH- ions. • Relative amounts determine whether the solution is acid, base, or neutral • Acid soln – more H+ (Hydronium ion) • Basic soln- more OH- • Neutral- equal amounts of each
Which solution is Acidic? Basic? Neutral??? H+ OH- H+ OH- OH- H+ Acidic Neutral Basic Solution Solution Solution
Arrhenius Model • Acid is a substance that contains hydrogen and ionizes to produce hydrogen ions in aqueous solns • Base is a substance that contains a hydroxide group and dissociates to produce a hydroxide ion in aqueous solns • Shortcomings- NH3 (Exception)
Acids and Bases • Produce OH- ions in water • Have a bitter taste and a slippery feel • Break down fats and oils • Formula ends with OH • Poisonous and corrosive to skin • pH greater than 7 • Produce H+ ions in water • Have a sour taste • Break down metals • Formula starts with H • Poisonous and corrosive to skin • pH less than 7
Acid ConjugateBase Brønsted-Lowry Model • Acid- hydrogen ion donor • Base- hydrogen ion acceptor • HX (aq) + H20 (l) H30+(aq) + X-(aq) Base ConjugateAcid
Conjugates • Conjugate Acid • Species produced when a base accepts a hydrogen ion from an acid • Conjugate Base • Species that results when an acid donates a hydrogen ion to a base • Conjugate acid- base pair • Consists of 2 substances related to each other by donating and accepting of a single H+
Conjugates • HF + H2O H3O+ + F- (H3O+ Conjugate acid) (F- Conjugate base) • NH3 + H20 NH4++ OH- (NH4+ Conjugate acid) (OH- Conjugate base) • Amphoteric- substances that can act as both acids and bases • Monoprotic- HCl, HF • Polyprotic- H2SO4, H3PO4
Acid Strength • Strong acids – ionize completely • Weak acids- do not ionize completely Ka = HCN + H2O H3O+ + CN- Ka =
Practice Problems • Write an ionization equation and acid ionization constant expression for Nitrous Acid. • HNO2 HNO2 + H2O H3O+ + NO2- Ka =
One More Practice Problem • Write an ionization equation and acid ionization constant expression for Chlorous Acid. • HClO2 HClO2 + H2O H3O+ + ClO2- Ka =
Base Strength • Strong Bases- completely dissociate into metal ions and hydroxide ions • Weak bases- partially dissociate Base ionization constant Kb =
Practice Problems Write ionization equations and base ionization constant expressions for the carbonate ion. CO32- CO32- + H2O HCO3- + OH- Kb =
One More Practice Problem • Write ionization equations and base ionization constant expressions for the hydrogen sulfite ion. • HSO3- HSO3- + H2O H2SO3 + OH- Kb =
pH • Measure of H+ ions in soln • pH = -log[H+] • Acidic solutions have a pH below 7 • Basic solutions have a pH above 7 • pH 7 is neutral • Change of 1 pH unit represents a tenfold change. (exponential)
pOH • Measures concentration of OH- ion pOH = - log [OH-] pH + pOH = 14.00
Practice Problems • Calculate the pH and pOH of aqueous solutions having the following ion concentrations. [OH-] = 6.5 x 10-6 pOH = -log[OH-] pH = 14.00 – pOH pOH = -log[6.5 x 10-6] pH = 14.00 – 5.19 pOH = -[log 6.5 + log 10-6] ph = 8.81 pOH = -[0.81 + (-6)] pOH = 5.19
One more, one more time! • Calculate the pH and pOH of aqueous solutions having the following ion concentrations. [H+] = 3.6 x 10-9 pH = -log[H+] pOH=14.00 – pH pH = -log[3.6 x 10-9]pOH=14.00-8.44 pH = -[log 3.6 + log 10-9]pOH=5.56 pH = -[0.56 + (-9)] pH = 8.44
Buffers • A buffer is a mixture of a weak acid and its conjugate base OR, a weak base and its conjugate acid. • This mixture resists changes in pH. • The amount of acid or base a buffer can absorb without significant change in pH is called the buffer capacity.
Neutralization Reactions • When an acid is added to a base, the end products are always salt and water. (neutral) • A salt is defined as the neutral end product of an acid/base reaction. ACID + BASE SALT + WATER H2S + Ca(OH)2 CaS + H2O • What is wrong with this equation???
Balance the final equation! H2S + Ca(OH)2 CaS + H2O 1 Ca 1 1 S 1 4 H 2 2 O 1 H2S + Ca(OH)2 CaS + 2 H2O
Neutralization Reactions Try another example: Acid + Base Salt + Water H2SO4 + NaOH Na2SO4 + H2O 1 Na 2 1 SO4 1 3 H 2 1 O 1 H2SO4 + 2 NaOH Na2SO4 + 2 H2O
Take it one step further… Sulfurous acid and sodium hydroxide yields sodium sulfite and water. H2SO3 + NaOH Na2SO3 + H2O 1 Na 2 1 SO3 1 3 H 2 1 O 1 H2SO3 + 2NaOH Na2SO3 + 2H2O
One Last Step Hydrosulfuric acid and calcium hydroxide yields what??? H2S + Ca(OH)2 • One product will always be water. H2S + Ca(OH)2 H2O + • The other product will be the + ion of the base bonded with the – ion of the acid. H2S + Ca(OH)2 2H2O + CaS
pH Indicators • A chemical substance that changes color in the presence of an acid and/or a base. 1) pH paper – Dip the paper, match color to scale on vial to determine numeric pH. pH<7 = acid, pH>7 = base, pH = 7 neutral 2) Litmus – Dip one red and one blue paper. Red stays red, blue turns red Acid Blue stays blue, red turns blue Base Red stays red, blue stays blue Neutral
pH Indicators 3) Bromthymol Blue – Add a few drops of bromthymol blue to the substance. If the blue color turns to yellow Acid If the blue color stays blue Base 4) Phenolphthalein – Add a few drops of phenolphthalein to the substance. If the clear liquid turns to pink Base If the clear liquid remains clear Acid