Chemical Reactions Chapter 13

Acids Have a sour taste. Vinegar owes its taste to acetic acid. Have a sour taste. Vinegar owes its taste to acetic acid. Citrus fruits contain citric acid. React with certain metals to produce hydrogen gas. React with certain metals to produce hydrogen gas. React with carbonates and bicarbonates to produce carbon React with carbonates and bicarbonates to produce carbon dioxide gas. Cause color changes in plant dyes. Cause color changes in plant dyes. 2HCl (aq) + Mg (s) MgCl 2 (aq) + H 2 (g) 2HCl (aq) + CaCO 3 (s) CaCl 2 (aq) + CO 2 (g) + H 2 O (l) Aqueous acid solutions (aq) conduct electricity. Aqueous acid solutions (aq) conduct electricity.

Have a bitter taste. Have a bitter taste. Feel slippery. Many soaps contain bases. Feel slippery. Many soaps contain bases. Bases Cause color changes in plant dyes. Cause color changes in plant dyes. Aqueous base solutions (aq) conduct electricity. Aqueous base solutions (aq) conduct electricity. ammonia hydroxide ion

(“milk of magnesia”)

acid - a hydrogen ion donor base - a hydrogen ion acceptor acidbase A hydrogen ion, H +, is the same as a proton!

Hydronium ion, hydrated proton, H 3 O + Electron-rich region Electron-poor region Figure 13.3 H H H O

acid base acid - a hydrogen ion donor base - a hydrogen ion acceptor acid base

Neutralization Reaction acid + base salt + water HCl (aq) + NaOH (aq) NaCl (aq) + H 2 OSalts HCl (aq) + KOH (aq) KCl (aq) + H 2 O

Neutral Solutions: Acidic, Basic or Neutral HCl (aq) + H 2 O (l) → Cl ˉ (aq) + H 3 O + (aq) acidbase acidbase NH 3 (aq) + H 2 O (l) ⇌ NH 4 + (aq) + OH ˉ (aq) Water is amphoteric – can behave as an acid or base

How do we express the concentration of an acid or a base? pH scale – based on concentration of the hydronium ion (H 3 O + ) acidicbasicneutral Based on powers of 10: e.g., a soln with pH = 3 is 10 times more acidic than a solution with pH = 4

Common substances that are acidic

pH Values of Some Common Solutions

Red Cabbage Juice Used to Determine pH

Oxidation-Reduction (Redox) Reactions (electron transfer reactions) 2Na (s) + Cl 2 (g) 2NaCl (s) 2Na 2Na + + 2e - Cl 2 + 2e - 2Cl ˉ Oxidation half-reaction (lose e - ) Reduction half-reaction (gain e - ) 2Na + Cl 2 + 2e - 2Na + + 2Cl - + 2e - 2Na + Cl 2 2NaCl

2Na (s) + Cl 2 (g) 2NaCl (s) Na is the reducing agent Cl 2 is the oxidizing agent Reducing agents (be oxidized) Oxidizing agents (be reduced)