1 Acids and Bases

2 Properties of Acids and BasesWater soluble Electrolyte Sour Bitter Corrosive Feels like water Feels slippery, like soap/wax Turns litmus paper red Turns litmus paper blue Neutralizes bases Neutralizes acids Reacts with active metals to form H2(g)

3 Svante Arrhenius Developed the Arrhenius acid-base theoryAcids produce H+ ions in solution Must have at least 1 hydrogen Ex. HCl, H2S, CH3COOH Bases produce OH- ions in solution Have OH-, ex. NaOH, or react with water to form OH-, ex. NH3

4 Svante Arrhenius When acids or bases are dissolved in solution they undergo ionization and separate into their ions NaOH  Na+ + OH- HCl  H+ + Cl-

5 Hydronium H+ ions in solution react with water to form H3O+, an ion called Hydronium Small amounts of hydronium are also formed by water reacting with itself: 2 H2O ↔ H3O+ + OH-

6 Hydronium Hydronium in solution is the source of acid- base chemistry.The amount present in water is pH-neutral Higher concentrations of hydronium leads to acidity Lower concentrations of hydronium leads to being a base

7 Strong Acids and Bases When ionic acids and bases are dissolved in water they dissociate completely. Virtually every molecule will split into ions(99+%). H2S  2 H+ + S2- 1 mol of H2S dissociates into 2 mol of H+ and 1 mol of S2- These solutions are called strong acids and strong bases

8 Weak Acids and Bases When covalent acids and bases are dissolved in water they only dissociate partially. Only some molecules will split into ions. CH3COOH ↔ CH3COO- + H+ 1 mol of CH3COOH dissociates into mol of CH3COO- and H, with mol of CH3COOH remaining These solutions are called weak acids and weak bases 1.3%

9 Weak Acids and Bases STRONG ACID/BASE WEAK ACID/BASE Ionic CovalentComplete dissociation Partial dissociation Better electrolytes (more ions) Worse electrolytes (less ions)

10 Strength Vs. ConcentrationH+ or OH- concentrations are affected by Acid/Base Concentration: “How much acid/base is in this solution?” Acid/Base strength: “How much of it split into ions?”

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12 pH A simple measure of acidity, usually ranging from 0- 147 is neutral (pure water) 0 is very acidic 14 is very basic

13 pH So why 0-14? Most acids and bases have a hydronium concentration from 1.0x100 to 1.0x mol/L They just used the exponents and dropped the negative sign! 1 pH difference is a 10x change in concentration of H3O+. 2 pH = 100x, 3 pH =1000x, etc.

14 pH pH = - log[H3O+] [H3O+] = 10-pHReminder: [Chemical] means concentration in mol/L

15 Measuring pH Indicators are chemicals that change colour under certain pH Phenolphthalein; colourless in acid, hot pink in base

16 Measuring pH Digital pH meters have a glass electrode that changes in conductivity when it interacts with Hydronium. This lets it measure pH.