Chapter 15: Acids & Bases

CHE 124: General Chemistry IIDr. 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

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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

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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

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Properties of Acids• Sour taste• React with “active” metals– i.e., Al, Zn, Fe, but not Cu, Ag, or Au

2 Al + 6 HCl AlCl3 + 3 H2

– corrosive

• React with carbonates, producing CO2

– marble, baking soda, chalk, limestone

CaCO3 + 2 HCl CaCl2 + CO2 + H2O• Change color of vegetable dyes– blue litmus turns red

• React with bases to form ionic salts 6

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Common Acids

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Structures of Acids

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• Binary acids have acid hydrogens attached to a nonmetal atomHCl, HF

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Structure of Acids

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• Oxy acids have acid hydrogens attached to an oxygen atomH2SO4, HNO3

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Structure of Acids

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• Carboxylic acids have COOH groupHC2H3O2, H3C6H5O7

• Only the first H in the formula is acidic the H is on the COOH

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Properties of Bases

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• Also known as alkalis• Taste bitter

alkaloids = plant product that is alkalineoften poisonous

• Solutions feel slippery• Change color of vegetable dyes

different color than acid red litmus turns blue

• React with acids to form ionic saltsneutralization

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Common Bases

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Structure of Bases

• Most ionic bases contain OH− ions– NaOH, Ca(OH)2

• Some contain CO32− ions

– CaCO3 NaHCO3

• Molecular bases contain structures that react with H+

– mostly amine groups

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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

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