Transcript Slide 1
10.1 Acids and Bases Learning Goals … … identify properties of acids and bases … calculate the pH of an acid … calculate the hydrogen ion concentration of an acid … identify acids and bases as strong or weak THE ARRHENIUS THEORY If an acid or a base is soluble in water, we know that it dissociates into its ions ACIDS BASES HCl (aq) H+(aq) + Cl-(aq) NaOH(aq) Na+(aq) + OH-(aq) HBr (aq) H+(aq) + Br-(aq) LiOH(aq) Li+(aq) + OH-(aq) H2SO4 (aq) 2H+(aq) + SO42- (aq) Ba(OH)2(aq) Ba2+(aq) + 2OH-(aq) an acid is a substance that dissociates in water to produce H+ ions a base is a substance that dissociates in water to produce OH- ions Properties of Acids and Bases Property Acids Taste sour Conducts Electricity yes Feel of Solution n/a Turns Litmus Paper red Reacts with Metals to produce H2 Reacts with Carbonates to produce CO2 Bases bitter yes slippery blue no no The pH Scale pH: The Power of the Hydrogen Ion • A measure of the amount of H+ ions in a solution • pH is a logarithmic scale, defined by using a scale of powers of 10 • every change in one pH unit on the scale represents a tenfold effect on the concentration of the solution The pH range is from 0 14 ACID pH < 7 BASE pH > 7 NEUTRAL pH = 7 The greater the concentration of hydrogen ion, the smaller the pH e.g. How much more acidic is: 10 (a) a pH of 2 than a pH of 3? (b) a pH of 2 than a pH of 5? 10x10x10 = 1000 pH = -log [H+] [H+] = 10-pH Locate the log and the 10x buttons on your calculator. Ex) Calculate the pH of a solution with a) [H+] = 4.2 x 10-4 mol/L pH = -log [H+] = -log[4.2 x 10-4 ] = 3.4 b) [H+] = 3.5 x 10-8 mol/L pH = -log[3.5 x 10-8] = 7.5 Ex) Calculate the [H+] if the solution has a a) pH of 9.6 [H+] = 10-pH = 10-9.6 = 2.5 x 10-10 mol/L b) pH of 3.8 [H+] = 10-3.8 = 1.6 x 10-4 mol/L Some acids may contain more than one proton… Monoprotic acids: • contain only one hydrogen • e.g. HNO3 Diprotic acids: • contain two hydrogens • e.g. H2SO4 Triprotic acids: • contain three hydrogens • e.g. H3PO4 Strong vs Weak Acids For an acid to be classified as ‘strong,’ it must have 100% ionization (completely dissociate into its ions in water) • Weak acids only partially ionize into its ions in water There are only six strong acids: Chemical Formula HCl HBr HI Name Hydrochloric Acid Hydrobromic Acid Hydroiodic Acid H2SO4 HNO3 HClO4 Sulfuric Acid Nitric Acid Perchloric Acid All other acids are weak: eg. CH3COOH, H3PO4 Any base that contains the OH- ion is is considered a strong base: eg. NaOH, KOH, Ca(OH)2 Weak bases do not contain OH-: eg. NH3 CAN I … … identify properties of acids and bases … calculate the pH of an acid … calculate the hydrogen ion concentration of an acid … identify acids and bases as strong or weak HOMEWORK p463 #5-16 WS “pH Practice”