Chapter 15: Acids & Bases CHE 124: General Chemistry II Dr. Jerome Williams, Ph.D. Saint Leo University

Overview Acids: Properties & Structures Bases: Properties & Structures Indicators

Stomach Acid & Heartburn The cells that line your stomach produce hydrochloric acid – to kill unwanted bacteria – to help break down food – to activate enzymes that break down food If the stomach acid backs up into your esophagus, it irritates those tissues, resulting in heartburn – acid reflux 3 Tro, Chemistry: A Molecular Approach, 2/e

Curing Heartburn Mild cases of heartburn can be cured by neutralizing the acid in the esophagus – swallowing saliva, which contains bicarbonate ion – taking antacids that contain hydroxide ions and/or carbonate ions 4 Tro, Chemistry: A Molecular Approach, 2/e

GERD Chronic heartburn is a problem for some people GERD (gastroesophageal reflux disease) is chronic leaking of stomach acid into the esophagus In people with GERD, the muscles separating the stomach from the esophagus do not close tightly, allowing stomach acid to leak into the esophagus Physicians diagnose GERD by attaching a pH sensor to the esophagus to measure the acidity levels of the fluids over time 5 Tro, Chemistry: A Molecular Approach, 2/e

Properties of Acids Sour taste React with “active” metals – i.e., Al, Zn, Fe, but not Cu, Ag, or Au 2 Al + 6 HCl  AlCl H 2 – corrosive React with carbonates, producing CO 2 – marble, baking soda, chalk, limestone CaCO HCl  CaCl 2 + CO 2 + H 2 O Change color of vegetable dyes – blue litmus turns red React with bases to form ionic salts 6 Tro, Chemistry: A Molecular Approach, 2/e

Common Acids 7 Tro, Chemistry: A Molecular Approach, 2/e

Structures of Acids 8 Binary acids have acid hydrogens attached to a nonmetal atom HCl, HF Tro, Chemistry: A Molecular Approach, 2/e

Structure of Acids 9 Oxy acids have acid hydrogens attached to an oxygen atom H 2 SO 4, HNO 3 Tro, Chemistry: A Molecular Approach, 2/e

Structure of Acids 10 Carboxylic acids have COOH group HC 2 H 3 O 2, H 3 C 6 H 5 O 7 Only the first H in the formula is acidic the H is on the COOH Tro, Chemistry: A Molecular Approach, 2/e

Properties of Bases 11 Also known as alkalis Taste bitter alkaloids = plant product that is alkaline  often poisonous Solutions feel slippery Change color of vegetable dyes different color than acid red litmus turns blue React with acids to form ionic salts neutralization Tro, Chemistry: A Molecular Approach, 2/e

Common Bases 12 Tro, Chemistry: A Molecular Approach, 2/e

Structure of Bases Most ionic bases contain OH − ions – NaOH, Ca(OH) 2 Some contain CO 3 2− ions – CaCO 3 NaHCO 3 Molecular bases contain structures that react with H + – mostly amine groups 13 Tro, Chemistry: A Molecular Approach, 2/e

Indicators Chemicals that change color depending on the solution’s acidity or basicity Many vegetable dyes are indicators – anthocyanins Litmus – from Spanish moss – red in acid, blue in base Phenolphthalein – found in laxatives – red in base, colorless in acid 14 Tro, Chemistry: A Molecular Approach, 2/e